72 Volt Upgrade – Introduction

All the ingredients of the 72V upgrade have been discussed already in this blog and others like it, as well as in places like the Electric Motoring Forum. But a lot of people just want the ‘recipe’ in one convenient chunk.

It’s not actually quite as simple as this as there are subtly different ways of solving some of the problems confronted by upgrading to a 72V system. There are also many different opportunities to reconfigure the existing system, or to add new features, such as regenerative braking or cruise control. You will want to decide how far you want to go with this upgrade, and how important it is for you to preserve things like range while adding the extra power needed to make it act more like a ‘proper’ bike.

There are four main areas of consideration that need to be born in mind when upgrading to a 72V system:

1. Batteries and Power System Cables

The first thing you should do is upgrade the power cables with something a little more substantial. You don’t have to do this if you’re using just a basic 72V controller, but I would recommend it, as the existing wiring on the 48V bikes is a bit flimsy. The thicker the cables, the less resistance there will be in the system, and the more current can be drawn without the risk over-heating. Upgrading the cables in this way means better performance and one less bottle-neck in the system; it also means you’ll be able to use any controller you want, and draw as much current as the motor is capable of handling (and then some).

If you just want to get up and running quickly with a basic controller, then you can skip this part and come back to it later if you upgrade to a better one, but my instructions on fitting the controller assume that you’ve done this, and that you’ve included an anderson connector in your new arrangement. If you want to skip this part of the work, you’ll have to improvise a little to take this into account.

Prepared for the Upgrade – Welding Cables replace existing Battery Wiring

If you’ve committed yourself to the upgrade and already ordered the parts you’ll need, this is a good thing to spend time on while you’re waiting for them to arrive. That way you can have all the cables needed for the existing and extended battery system ready for when it comes time to wire in the controller. You can also have the main part of the work (the controller) done in a single evening, so you’re not off-the-road for too long.

To actually charge the new battery bank, you’ll also need a 72V charger. These can be found on eBay but will probably have to be ordered from China. my shop now does a 72V charger suitable for this purpose.

2. 72V Controller and Connections

eBay has many merchants selling stock, budget controllers, most of which appear identical, but usually need to be ordered from China and have little if any documentation. If you definitely want regenerative braking, though, it’s best to stick with the well documented (but more expensive) Lyen’s “Extreme Modder” Edition (reviewed here and here) or e-crazyman controller, as these can include a programmable interface so that they can be set up with the right regen voltage for the Ego Scoota.

A typical, stock 72V Controller

If you expect to be relying heavily on your bike, then it might be worthwhile getting an extra, cheap one as a spare. That way you can be up and running quickly if this essential unit breaks down.

The connectors on the controller will also need changing to some degree to make them compatible with the bike. If the phase wires don’t come with 6mm ring connectors then these will need to be added, and the power wires will need to be hooked up to an Anderson connector  which can accommodate the thicker cable we’ll be using on the battery bank. A two-pin mini-connector will also be needed for the brake cut-off and power-feed wires on the Ego’s loom.

3. Running the 12V system

Once you upgrade to 72V, the 48-12V converter that provides power to the 12V system for the headlights, indicators etc. will no longer work. The crucial connector Bk/Y/R that converts the full battery bank voltage into 12V will need to be served by something else. Quality 72V versions of these (they will actually allow any input from 20-90V) are now available from my shop. The unit has exactly the same connector as the 48V converter that comes with the bike, and can therefore be mounted ‘plug and play’ in the same position as the old one. Since it can function with the original 48V input voltage, it is also a good place to start for an upgrade as it will still work fine with the original battery bank.

The 72-12V DC-DC Converter

Alternatively you can use Mike’s recipe to modify a PSU for this purpose, but bear in mind there can be complications (as with myself) when the polarity of the unit varies, and you can end up with -12V instead of +12V coming off the final product. This will require a couple of wires switching – the 12V and the ground.

If you don’t have a suitable converter available, you can set up a workaround by simply powering the 12V system from a single battery, either a separate one, or an existing bank-battery. Bear in mind, though, that this battery will go out of balance more easily with prolonged use and may require topping up. But this is easy enough to do through a homemade connector that can allow you to charge the battery from the connector that hooks it up to the loom.

The loom connector for the 12V system supply. As an interim solution, it is fed here by a lead from the first battery in the bank

Out of these alternatives, I’d recommend the replacement 72V converter available from my shop, as it’s built for this specific purpose, is as cheap as (if not cheaper than) the PSU-based solution and is also much more energy-efficient.

4. Adapting or Replacing the Battery Meter Setup

Another problem is that the Battery Meter will no longer function. There are three main ways that people take care of this. One solution involves running a lead off of the positive terminal of Battery 4 to provide the 48V that the existing meter requires. However this solution also requires a relay to be attached so that the 48V is only applied when the ignition is on. Another solution is to use a zener diode to drop the voltage of the battery meter terminal on the upgraded system back down to the 48V required.

The third solution is the route I opted for, which is to simply replace the existing battery meter for a better unit. I collaborated with Sparklight Products to customise their 6-LED, 12-state battery meter and bring it out as a kit suitable for the Ego Scoota. This kit is available in 48V, 60V and 72V form.

The meter is much better than the existing one, and very affordable (a tenner plus change). If you like tinkering around, and don’t mind the work involved in refitting the meter then this is probably the solution for you.

The Sparklight Products 6-LED, 12-State Battery Meter

This guide is split into five parts:

• 4.2.1. Upgrading the Power Cables (optional)
• 4.2.2. Building a 72v DC Converter (optional)
• 4.2.3. Cutting a Hole for the Extra Batteries
• 4.2.4. Preparing the Controller Connectors
• 4.2.5. Installing the 72V Controller

If you go through all five parts of this in order, it should be hard to go wrong. With the availability of the Thunderstruck 72-12V converter unit, 4.2.2 can be skipped if you take this route. Regenerative braking isn’t covered as yet, but that will probably be coming soon. Remember to get a Lyen’s “Extreme Modder” Edition or  e-crazyman  controller if you definitely want that feature, as most cheap controllers don’t support this feature or explain how to make it work.

Installing the 72V Controller

Parts

• A 72V Controller
• One 3-way motorcycle mini-connector (if taking 12V system from a single battery)
• Two 12V 28AH batteries (like the existing batteries)
• The extra connectors you made in Upgrading the Power Cables
• A selection of various crimps might come in handy

Tools

• A screwdriver with socket and phillips head attachments
• A pair of wire snippers
• A multimeter

At this point…

At this point you should have upgraded your power cables with the nice thick welding cable or at least something better than what was there before. You will also have the four cables you were left with; two to string the batteries together, and the remaining ones that go from the master terminals to the Anderson connector that will serve power to the controller.

If you built a DIY 72V adaptor then you will also have this, or a suitable substitute. If you just want to rig the 12V system up to one of the batteries for now, then you’ll need a cable composed of a three-way connector rigged up to two 6mm ring connectors. You will also have the two extra batteries and all the other parts listed. You will also have checked the connectors on the controller and added the Anderson connector, a two-way mini-connector, and – if necessary – ring connectors to the phase wires.

If you’ve just cut your hole and intend to go straight on to the main job of fitting the new controller, then don’t bother bolting the seat back on just yet. It’s best to leave it until the new arrangement has been tested ‘loose’, so that everything can be easily accessed if something needs fixing. It can all be put back together nicely when we know it all works as it should.

Removing the Old Controller

The first thing to do is remove the old controller. A single bolt at the front, and a clip to the rear should be securing it to its mount. Next disconnect the three phase-wires from the three-way (six terminal) junction box, unplug the hall sensor connector, brake connector and throttle connector, and then disconnect the main black/red feed wires from their terminals on the 2-way ceramic block.

Preparing the Main Power Feed

The next thing your need to do is wire in the big cable you built with that Anderson connector at the end. This is the main power feed for the motor. The black connector goes from the master negative terminal (top left) to somewhere near the 2-way ceramic block (just by the breaker switch) where the old power terminals are located.

Top Left to Right you can see the Negative Lead running to the Anderson Connector

The red, positive lead goes straight from the output (ON/OFF) side of the breaker switch to the Anderson connector. This will power the new controller’s main motor-feed circuit.  The ceramic block will no longer be needed, as power to the controller will be taken from this new line instead.

The Anderson connector, with the positive about to be connected to the breaker switch

Why are We re-wiring this Bit?

If you look at the output of the breaker switch on the existing system, you’ll see one main, red power wire leave the breaker and enter the loom. This wire then loops back up the loom alongside a black ground wire, and re-emerges at the top to join with that ceramic block which currently powers the controller.

However it turns out that the length of wiring inside the loom breaks off to serve the ignition, so you can’t just dispense with this length altogether. The main power cable of our new arrangement, though, really doesn’t need to go all the way round to where it serves the ignition feed. It makes more sense to break our power feed away earlier, and take it directly from the breaker switch to the Anderson connector. It doesn’t affect the actual connectivity of the system doing it this way, provide we retain the length of wire up to the ignition feed and back to its earth-source.

So the first thing to remember, here, is that the red wire going from the breaker into the loom must remain, as must the black wire that goes from the master negative and up into the loom. These are both needed for the ignition circuit – DO NOT REMOVE THESE.

However you can remove the ceramic block, and cut off its two R/Bk wires where they emerge from the loom, as below.

The wires that formerly served the ceramic block have been cut off at the top of the loom (the length within the loom is spared as it serves the ignition feed)

This all done, you should be ready to add the new batteries to complete the 72V bank, and wire in the new controller.

Assemble the new Battery Bank and test the 12V System

You can now wire the new 72V battery bank together. Be careful here, and think carefully about what you connect to what. If you have any doubts, use your multimeter to figure out where you are. Keep the breaker switch OFF until you’re ready to test the new configuration, but don’t be lulled into a false sense of security as you wire up that battery bank. 72V might not be lethal, but it can spray you with sparks and molten metal if you get things wrong.

When you’re ready, turn the breaker switch to the ON position and take multimeter readings to confirm that 72V is being delivered to the bike’s system.

If you built the DIY 72V-12V converter then now is the time to test it. Hook it up to the R/Y/Bk three-way mini-connector on the bike’s loom that used to host the old adaptor and switch on the ignition. The green light should glow dimly and the electrics should work as they did before. At this point you might also want to test the indicators; if the polarity on the DIY unit is wrong (-12V rather than +12V) then the blinker unit won’t work and the indicators will fail.

Testing the DIY 72V adapter

If you bought the 72V-12V converter (as I’d recommend for this upgrade), then you just replace the existing 48V converter with this instead. In fact, since the converter will run off of 20-72V, you can replace this as the first part of the upgrade, as it should still work with the scooter in its original 48V configuration.

The 72-12V converter

Wire in the Controller

All that remains now is to wire in the controller to its corresponding connectors on the loom. You might want to leave the controller ‘loose’ as you connect up the cables and figure out how to physically route them all round to where they need to be. Then you can bolt the controller in properly once everything is working.  Turn the breaker switch back to OFF until all your connectors are properly hooked up.

1. The Main Power Connector

This is straightforward enough. In the last section you should have attached all the right connectors to the Controller, including the Anderson for the main motor power. This now just plugs into the Anderson connector on the loom: Just make sure you have the black/red wires the right way round.

2. The Phase Wires and Hall Connector

The three Bl/Gr/Y phase wires just hook up to the big three-way junction where the old ones went. Colours seem to be standardised as far as these connectors are concerned, but there are rumours that these sometimes need reversing to make things work. I have yet to see this problem, so start with checking the throttle connector if things don’t start up straight away, as this is often the culprit.

Once you’ve connected the phase wires, check the six-pin Hall sensor connector (Bl/Gr/Y/Bl/R) on the new controller and plug that into its counterpart on the loom. On both controllers I’ve had, there has never been an issue with this connector.

3. The Brake/’Ignition’ and Throttle Connectors

Next comes the two-way brake/power feed connector, and the R/Bk/Gr three-way throttle connector. Below you can see these connectors as they were hooked up to the old 48V controller:

BEFORE: The original brake/’ignition’power feed (left) and throttle cable (right) arrangement with the 48V controller

On the new controller, you simply connect up the two-way R/W connector you attached for the brake/power feed, along with the new R/Bk/Gr throttle connector.

For the two-way brake/’ignition’connector (below right), the green from the bike’s loom (which comes off of the brake-light circuit), goes to the white wire on the controller. The red wire on the loom (which comes from 72V circuit) goes to the thin red wire on the controller. If you have any doubts about the which wires from your bike go where, then measure them with a multimeter. The red 72V wire should measure 70-76V or so when the ignition switch is ‘on’. The green wire should measure around 12V when the brake is operated or the sidestand switch is activated.

For the three-way throttle connector, you need to MAKE SURE THE THROTTLE CONNECTOR WIRES MATCH UP! The colours either side should all match (though the ones on the loom may have a white stripe as below). The red, black and green wires on one side of the connector should meet the red, black and green wires on the other side. If they don’t match, then pick them and swap them round on the controller side.

AFTER: The new brake/’ignition’ power feed (right) and throttle cable (left) arrangement with the 72V controller

Once everything is connected up okay, you can turn on the breaker switch and see if it all works.

Fire it up!

This is the moment you’ve been waiting for. But don’t panic too much if nothing happens right away, as you probably forgot something basic.

First check that the bike is firmly on its stand with the rear wheel raised clear of the ground. Turn the ignition key and gently turn the throttle. If the motor whirrs to life, then congratulations, you evidently did everything right. Squeeze the brake at the same time as the throttle to make sure the throttle cut-off works (the brake should cut off power to the motor).

If nothing happened then:

1) Do one more check of the voltage on the main power wires. Is power actually getting through to the controller? Is there any power at all? Are the batteries all wired up properly, with no breaks in the circuit?

2) Is the brake light on? If so, did you perhaps leave the side-stand slightly down so that the brake cut-off is in operation?

3) Are you sure that THROTTLE CONNECTOR is properly wired up? If you checked all of these things and are still having no joy, then you might have bought a dead controller and may need to return it. Did you buy a spare? If so, you can try that one too. If not, then you’re out of luck and will need to ‘revert’ to 48V mode until you can figure out what’s up.

If you just can’t figure out what the problem is, then you can post a message here or to the Electric Motoring Forum.

Preparing the Controller Connectors

Parts

• A 72V Controller
• One Anderson Connector (the other half of the pair you got for Upgrading the Power Cables)
• One 2-way motorcycle mini-connector
• A selection of various crimps might come in handy

Tools

• A soldering iron and solder wire is desirable but not essential
• A pair of wire snippers
• A pair of crimpers
• A multimeter

The next thing to do is prepare the connectors on the new controller so that they can connect securely to the bike’s system. Your controller should be something like the one below. For the upgrade we only need concern ourselves with connectors A-F. You can forget about connectors H, J, K, though if you want cruise-control, you could wire G into one of your horn buttons (the one you don’t use).

Generic 72V Controller

• A – Main Motor Power Feed (R +72V, Bk Gnd): To main battery bank +/- terminals
• B – Phase Wires (Bl, Gr, Y): To corresponding wires on connector block.
• C – Hall Sensor: To corresponding connector on loom
• D – Throttle Connector (Bk, Gr, Red). Warning! – Wires in connector may be reversed.
• E – Brake Cut-off: To brake/sidestand 12V line (meets 2-pin Gr, R/Bk connector on loom with F)
• F – Controller Power Feed: To R/Bk in 2-pin Gr, R/Bk connector on loom with E. (N.B: This spade fitting comes as part of the A connector)
  
• G – Cruise Control Switch: Short to ground briefly to set cruise level (for use with button)
• H – 60°/120° Option Switch: Open for 120° (Ego Motor  is 120°)
• J – ‘Alarm’ (details unknown)
• K – ‘Alarm Setting’ (details unknown)

The Power Cable & Anderson Connector

This is really the most important connection of the whole bike. However the wires from the controller are quite a bit thinner than the crimps for the Anderson connector, so – like others in the Electric Motoring Forum – I elected to ‘double-crimp’ these by using the existing connectors on the wires as ‘fodder’ for the larger crimps.

Here’s the main motor power cable as it came on my controller. It came as one of three spade connectors housed in a triangular-style three-pin plug with the ground and the low-current feed-wire for the controller. Since this connector isn’t in use on our bike, it needed dismantling into its component wires. This and the black (ground) wire need to be crimped into an Anderson Connector to connect with the one served by the main power cables on the bike. The low-current wire (the other red wire, F) will be connected up to the two-pin mini connector that also takes the the brake wire.

If you have different connectors on your power leads you can still use this method – or a variation – to good effect. If you have bare wires, you could crimp/solder them onto bullet connectors first, as with the instructions for the phase wires.

First I just folded over the spade  so it fits inside the Anderson crimp.

To pad out the crimp for a tight fit, I’ve used 10mm lengths of thick copper wire I took from an old cooker cable.

I pack the spade connector in with this ‘filler’ then crimp it for a good solid connection.

Next a bit of heat-shrink for insulation before it is clipped into its Anderson connector along with the black ground-wire.

The Anderson connector for the controller (left) is now ready to be joined with its counterpoint on the loom.

The Anderson Connector (left) for the controller power cables, connected to its counterpart (right) which takes power from the main battery bank via the breaker switch.

The Brake/Power Feed 2-way Connector

On the Ego Scoota, the white brake cut-off wire (E) and the red power feed (F) to the controller both need to hook up to the R/Gr female 2-pin that served the R/Vi wires on the old 48V controller. You therefore need to wire these in to the male two-pin mini-connector listed in the parts.

If you’re desperate, you can just take the one off the old controller, but it’s nicer to just use a fresh one, as whoever inherits your old controller won’t be too happy.

The final arrangement for the brake/power feed wires: A two-pin connector replaces the red/violet two-way that ran from the old 48V controller, and which now holds the equivalent red/white connections from the 72V controller.

The Phase Wire Ring Connectors

If you’re lucky, the phase wires on the controller you have will already have ring connectors. And if you are even luckier, the holes will be big enough that you won’t have to drill them out (beware!) or just replace them.

However if you are left with just some bare wires, you might be wondering how to give these a solid connection to the large-bored ring connectors you’ll need for the connecting block on the Scoota. The smallish guage phase wires are way too small to suit the large bore of a standard 6mm ring connector. However they are just the right size, for one of the many bullet connectors I got in my handy megapack of connectors.

To get rid of the plastic, two or three seconds under a lighter softens it enough to slide off with very little persuasion, and with no gooey mess…

which is great if you want to add a smidgeon of solder to the resulting crimp, like I did, to make sure the connection is as solid as possible.

With the phase wire bullet connection duly crimped and soldered, I then shoved it into the bore of the 6mm ring connector (not forgetting to slide a length of heat-shrink down the wire first).

Next I used the honking great crimper to crush it into a nice, solidly fused mass, then packed the heatshrink around the resulting join.

The Throttle Connector

The throttle connector on the controller should be a 3-way mini-connector just like the one on the loom. However you need to check this as the wires are frequently reversed, as below on my chatparts.com controller.

Watch out for that hinky throttle connection!

The Green(/White) – Black(/White) – Red(/White) throttle connector on the loom (bottom), corresponded to the Black-Green-Red on the controller’s own connector (top). This should be Green-Black-Red, NOT Black-Green-Red, so that they match their counterparts on the loom. On both of the controllers I have used, the black and green wires on the controller’s three-way connector needed ‘picking’ so that these wires could be reversed.

The problem, of course, may not take this form on every machine, or even exist at all, but whatever your configuration you need to make sure that the colours match up either side of the connectors.

Once you’ve got these four sets of connectors checked or fixed, the controller will be ready to attach to bike in the next section Installing the 72V Controller.

Cutting a Hole for the extra Batteries

The first thing to do to do for the upgrade is to prepare the bike for its two extra batteries. The underseat space – as well as providing storage space for luggage – is also an ideal location for the extra batteries, and the makers designed the underseat compartment with this in mind. A hole can be cut in its base to house two extra batteries such that they rest on top of the existing battery bank. This means, of course, that you need to remove the seat and cut a hole in it to accommodate the extra batteries.

The seat is attached by two flanged, hex-head bolts front and rear, and one phillips head screw. First remove these and put them somewhere safe.

Front under-seat compartment (one bolt already removed)

Rear

The seat is held onto the enclosure by one bolt that comprises its hinge. It is best to remove this while you are cutting the hole, as it makes the work much easier.

2. Cutting the Hole

Put your batteries together on a piece of paper and use them to trace an outline. Then cut out the square you marked out. This can be used as a template to mark the area of the seat enclosure that needs to be cut out.

Make a two-battery sized template to mark out the hole to be cut. (This is the single battery one I used for the 60V upgrade)

The underseat enclosure already has a groove cut into it as a guide for cutting a hole for two batteries (for a 72V upgrade). I made one side of my hole run along this groove, as it made cutting easier. I’ve not used the whole length they suggested though, as I wanted my battery to be a very snug fit so it doesn’t rattle around.

The photo below is one I took for my 60V upgrade, so the template is just for one battery. Imagine a piece of paper twice the width.

Mark it with a ruler and pen, or just score lines along with the blade of your knife as a guide to where you need to cut. Then carefully cut through the plastic with a fresh, sharp blade. The plastic is tough, so be patient.

Once done, test it for fit and adjust the hole until it’s nice and snug, but not so snug that it’s a struggle to get the batteries through. At this point it’s a good idea to also make two 6mm notches at the corners of the hole by the new bank’s master terminals either side. This will give you somewhere to feed the cables from the main battery bank below.

That done, you can put the seat back together and reattach it to the bike in preparation for the main work in Installing the 72V Controller.

Upgrading the Power Cables

Parts

• 2 meters 16mm² red welding cable
• 2 meters 16mm² black welding cable
• 12 welding cable crimp-on lugs for 16mm² cable – 6mm hole
• One Anderson connector
• A few lengths of 10mm heat-shrink

Tools

• A ratchet crimper
• A pair of wire snippers
• A stanley knife or other sharp blade

Introduction

If you want to upgrade your system to 60V or 72V by adding the extra battery or batteries, it is a good idea to also upgrade the power-cables connecting the batteries to one another and the rest of the system. This is a good way to spend your time while you’re pulling together the other parts you need, or waiting for for your 72V controller or battery charger to make its way from China.

The simplified schematic below shows the battery arrangement regarding the addition of batteries for the 60V/72V arrangement.

For your upgrade, you will therefore need to replace the existing cables, and also add a couple more to wire in the extra batteries (or battery) you will be adding as follows:

• Battery 1-2, 2-3, 3-4 & 5-6:  5 x 120mm (5″) BLACK
• Battery 4-5:  1 x 300mm (12″) BLACK
• Battery 6 to breaker switch input terminal:  1 x 450mm (16″) RED

When it comes time to wire in your new controller, you will need two more lengths of cable to run from the master positive (battery 6+) and negative (battery 1-) terminals. These following lengths will be connected to one side of an Anderson connector:

• Battery 1 to Anderson Connector:  1 x 600mm (24″) BLACK
• Breaker switch output terminal to Anderson connector:  1 x 120mm(5″) RED (though you may want to make this longer depending on where you wish to locate your Anderson connector for the final configuration)

Don’t take these measurements as gospel, they are for guidance only. They will depend on how you want to route your cabling around your system, or how much free play you like to have. The short lengths can be even shorter as they have so little distance to span and their length is taken up by a bend anyway.

Building the Cables

Most important of all, you’ll need one of these. It’s the only way you’ll get a good, solid connection. Use the orange section of the ‘jaw’ for these types of crimps.

Cut off the lengths you need (in this case about 120mm) for the four short lengths of battery-to-battery connector.

Take 10mm of the ends with a stanley knife or sharp blade. This should give you exactly the length of wire to fit it snuggly in the crimp-end of the 6mm lugs.

Crimp them with that honking great crimp tool. It requires a good amount of force even with the ratchet mechanism. If your hands aren’t so strong you might need to brace them against the floor and push down with your weight. Or else get Daddy to do it.

Next cut off a length of 10mm heat shrink and see to both ends of the cable (I just use a lighter to ‘set’ the heat-shrink). Neglecting this will leave you with hazardous lengths of exposed, live high-voltage cable

Beautiful. Just the bare minimum of exposed cable we need to secure our connections.

The final couple of lengths of cable that meet with the Anderson connector will not be needed until you are ready to install your new controller, these will need to be crimped at one end to the crimps used by your Anderson connector, so that they form a cable like this to be used in the final installation.

For the ends of the red cable running from Battery 6 to the breaker, and from the breaker to the Anderson connector, it is a good idea to tin them (that is, coat them in a layer of solder) so that they form a solid block that connects firmly with the breaker contacts.

And there you have it! The new wiring is now capable of carrying a whopping 170 amps, more than the ego’s motor will ever need, or can even withstand. Take a look and see how it compares to the flimsy wiring that it originally came with…

Thanks to Ian and Mike of the Electric Motoring Forum for pioneering this upgrade, and providing the details of the cables, connectors and tools required.

Building a 72V DC Converter

NOTE: This section was written before I found a supplier for a quality 72-12V converter. The unit has exactly the same 3-way mini-connector as the 48V converter that comes with the bike, and can therefore be mounted ‘plug and play’ in the same position as the old one. I would recommend this above building your own out of a PSU, as it’s built for this specific purpose, is more efficient and works out cheaper too.

Once batteries are added to the electrical system to raise the system to 72V, it is no longer possible to use the existing 48V factory converter which drives the 12V electrical sub-system. 72V converters are available to buy, but they are usually aimed at the marine market, and prohibitively expensive.

By modifying a more common, and relatively affordable LCD TV power supply unit, a perfectly adequate converter be fashioned to replace the existing redundant unit.

Mike of the Electric Motoring Forum has already documented this in his guide “Making the new DC converter”, but I’m also doing this as part of my ongoing upgrade activity. Much of this has therefore already been covered in his guide, but I have tried to improve upon the existing documentation by adding  more detailed explanations of the procedure along with a simplified explanation of the reasoning behind the rewiring schema. There are also quite a few more illustrations for clarity, and details of how to deal with the wiring in PSUs that don’t follow the circuit board layout for this particular model.

The modification to the unit is fairly straightforward. No extra parts need to be added. There is just a small amount of wiring and some soldering to do, and can be accomplished in a couple of hours or so by any reasonably capable DIY hobbyist with basic soldering skills.

Parts

• 12V 10A AC adapter for TV and LCD Monitor
• 3-way motorcycle connector
• A short length of red and black wire of around 17 amp grade
• A 22mm x 19mm square of plastic, such as a piece cut from a PTFE bottle or lid.

Tools

• A phillips head screwdriver
• A soldering iron and solder wire
• A multimeter
• A pair of wire snippers
• A crimper or needle-nose pliers
• A Stanley knife or other sharp blade

1) The LCD TV power supply unit

The power-supply unit as it comes consists of a box which is powered from the mains via a lead (not shown) plugged into a butterfly socket on the front end of the unit. The circuit board converts this into a 12V DC/1.5 amp power supply to serve an LCD display or TV via a 3.5mm plug at the end of a lead leaving the back end of the unit.

The circuitry, however, is capable of making a similar conversion on the 72V DC signal supported by the upgraded battery system.

2) Check the Unit

The first thing to do is plug the power supply unit (PSU) into the mains to make sure that it actually works. Once it has been tampered with, obviously it cannot be returned for a refund or replacement.

Plug in the unit and use a multimeter to confirm that the unit is giving out around 12V DC. Hold one contact against the side of the 3.5mm jack, and insert the other into the hole in its end, like so:

When you’re satisfied that the unit is functioning, then remove the mains lead and leave it for a few minutes to make sure that the capacitors have discharged.

3) Open the Case and remove the Circuit Block

On the back of the case, four screws are located underneath rubber grommets at the corners, that are used as the PSU’s ‘feet’. Peel off the grommets and undo the screws.

Remove the circuit block from its case by gently sliding it upwards to allow the socket to slide from its runners. It may be secured in place by a blob of glue on the base, in which case you may need to gently prise it free with a screwdriver.

4) Remove the metal casing from around the Circuit Block

The circuit block inside is encased in a metal wrapper held in place by two small rivets. To release the metal casing, just make a small cut with the snippers and fold back the metal to free it from the studs.

Underneath the metal casing, is a plastic insulating layer. Remove that too and set it aside.

We are changing the layout so that both the input and the output of the unit are on the same end, and served by a single plug that is compatible with the motorbike’s electrics. The existing socket will therefore have to be removed so that we can wire our own in its place.

If your PSU circuit board is identical to this one, then the illustrations will be an accurate guide as to where you need to solder the three connections we have to make. However, if the unit is different, you will need to clearly identify where the connections from the socket meet with the PCB and make a note of them, substituting the locations on your own board for the ones here.

Either way, you won’t have to worry about the earth connection beyond removing the lead used by the existing socket. Only the live and neutral terminals on the circuit board are used in our new schema.

The first step is to de-solder the existing plug and remove it.

Next, we need to prepare the output lead. Cut the plug off the output wire to leave about 12 inches of the cord remaining. Then feed the lead back through the case to the other end, where the socket for the mains was originally located. Strip back the insulation to where it passes the end of the circuit board, revealing the 12V out, live wire (blue) and the neutral (bare copper strand) wire. (The insulation tape over the black wire is just there to cover a split I found on the wire).

Thread this through the hole next to the one you just removed from the neutral solder-point. It shares the same terminal and will be cross-connected with our input neutral so that they are shared.

Solder it and clip off any extraneous length.

Next take your red and black wires and solder them to where you just removed the two black wires. The Red will be your 72V input, and it will go to the live terminal on the board, and the black will go to the neutral terminal alongside where you just soldered the copper strand, neutral output wire.

N.B: The blue wire (12V output) runs back through the circuit block to the other end where it originally emerged. The ‘black’ I used has a red stripe running down its underside that is visible from this angle.

Next, you need to cut a small piece of plastic to fill the hole left by the original mains input socket. You can get this from some household item like the side of a shampoo carton or a plastic lid (I used a piece cut from a Lynx shower gel bottle).

A square 22mm x 19mm forms a near exact fit. If you make the fit a little tighter, it can be held in place by the case itself once it is screwed shut, without the need for glue. Check the size of your cut-out by closing the plastic case around it.

Next, drill a 6mm hole through your plastic to feed the wires through which are to be joined to the 3-way motorbike connector.

Crimp the wires into the pin connectors for the 3-way socket, then push them through the back of the female end of the socket. The Black goes to pin 1, the blue goes to pin 2, and the red goes to pin 3, as they are viewed from the back (where the wires go in) with the latch facing down.

Refit the plastic and metal shielding, re-engaging the metal sheet with the rivets and securing with a drop of solder if required.

Finally slide the assembly back into its plastic case and screw it shut. If the plastic square does not stay firmly in place then a dab of glue, like epoxy resin can be put along the edges of the recess.

You should now have a fully functioning, plug-and-play converter that is compatible with 72V electrics!