Meltdown

The generic ‘Hua Tong’ controller does not take kindly to overvolting

Regenerative breaking

A few weeks after I bought and reviewed my LYEN Edition Controller, a freak occurence brought my fun to an untimely end. While I was rounding a bend of a smooth stretch of the one-way system that circles my town, I suddenly lost power and the bike came grinding to a halt with some nasty crunching noises coming from the controller.

Closer inspection made it immediately obvious what had happened. The main power wire that I had so solidly crimped into the Anderson connector running from the SLA bank that I was still powered by at the time had somewhow broken loose.

Uh-oh! the main power connector wire has come away…

In my optimism, I thought that it would simply be a matter of reconnecting the wire to bring the controller back to life again, but unfortunately it wasn’t as simple as this: The connection with the batteries had failed at a point when I was slowing, and when regenerative braking was feeding around 90V back into the batteries. The failure of the connector at this point had ugly repurcussions for the workings of the controller as it suddenly found itself with no place to send the power that was coming back through the controller as the bike switched to ‘dynamo’ mode. The result was a blown FETs and some other minor components whose repair are curently beyond my expertise.

I was pretty unhappy about this, and couldn’t understand how the connector could have failed in such a way. I’d gone to very great lengths to make sure the connection was solid, with the spade from the original controller connection being crimped solidly to the Anderson crimp with the aid of lengths of ‘filler’ that would guarantee a strong join.

To my relief, but also to my annoyance, it turned out that my crimp was completely sound, and that it was the neck of the spade connector from the controller itself that had failed, with the metal physically breaking rather than detaching from the wire as can so often happen. You can see from the picture below how the spade connector has physically snapped.

At first, I was baffled as to how this might have happened, but when I thought more about the layout it began to make sense. The controller wires weren’t very long, so they were a bit of a reach to the Anderson for the battery bank, and as a result they were slightly under tension.

This meant that the constant road vibration was making the connector bounce up and down, slowly fatiguing the metal at that crucial point. I took this unhappy incident as a lesson to tie down all my wiring with cable ties, and to see to it that any significant length of wire was never left in a position where it would be left flapping around.

Back to the McController

Diagnosing and replacing the blown components on my lovely new controller was unfortunately beyond my current expertise. I found a blown FET, but something else was wrong on the board too – probably one of those tiny surface mounted factory things that you need a microscope to even see properly –  so I reluctantly shipped it back to Lyen to fix for me. In the mean time I had to spend a few weeks back on one of my generic controllers, which was adequate enough, but no match for the zippiness and all round fun that the 4110 equipped  LYEN controller offered.

At this point though, I’d also just received my headway cells and all the components I needed for the Goodrum-Fechter BMS  and I was busily building my LiFePO4 pack and assembling the BMS. In the mean time, though, poor Eddy Lyen had gotten hurt after a spill off his bike during an electric rally event and was behind on his work, and so by the time I was ready to fire up my Lithium pack on my bike, my LYEN controller was still being fixed.

So for a week or so after my Lithium upgrade, I continued to run the bike on my budget, generic controller while I awaited the return of my LYEN. I had little choice though. I needed the bike to get to work and back, and it was also a way of seeing if the cheap controller with its inferior FETs could hack the higher operating voltage of a Lithium banks. The worst thing that could happen is that I destroy one of my spare controllers. This was no biggie, as I had another spare all wired up and ready to plug and play, and a whole box of factory new ones that I sell in my shop.

All seemed fine right up until I had my LYEN back just under two weeks later, and was about to put it back on again. An odd stutter on the way back from work concerned me slightly. Though it only happened once and very briefly, I nonetheless thought I should really not waste any more time in switching back over to my performance unit, and immediately took the seat off to remove the generic controller.

Straight away it was evident that the controller had been overheating to quite a serious degree. I really should have kept an eye on the temperature but with the long shifts I was working I’d gotten distracted by a dozen other things. The little plastic bushes on the case screws had completely melted and oozed through the holes in the case…

Likewise, the silicon sealant had at some point become runny and started to slither down the end-plate.

The reason for the controller’s unhappiness with the Lithium pack’s higher voltage is not at all surprising considering the nature of the unit and – particularly – the rating of the MOSFETs it uses.

It’s all about the MOSFETS…

The controllers I deal in use P75NF75 MOSFETs. When I first reported this to people curious about the type of FETS this budget unit uses, I was met with some tut-tutting and shaking of the head by more discerning enthusiasts. These FETs are officially rated for 75V, whereas a fully charged SLA bank will put out somewhere in the region of 78V. However an SLA bank’s peak voltage quickly decays to below 78V, and this 2-3% margin should be well within tolerance, and this is born out by the fact that tens of thousands of them are in circulation and doing their job without issue.

The LiFePO4 bank though, is another matter. I kept it properly topped up because I had no LVC and was relying on manual checks, and it was imperative that I didn’t allow any cells to unknowingly go flat. The LiFePO4 bank also spends for more of its discharge at above nominal voltage, so I was seldom going below 80V, and running the bike typically at 81-84V. The fact that it survived two weeks running at about 115% of its rated value – continuing to work even after it began melting – is a testament to how rugged these units are…

The LYEN controller and its ilk, though, with their IRFB 4110 MOSFETs, can take voltages of up to 100V, which is why you pay a premium for these deluxe controllers.

As a result of this experiment I’ve included some clarification on the sales blurb at my shop. As a precaution I’ve made it clear that these generic controllers should only be used with SLA banks. If you’re running a performance battery bank, then you need a performance controller to go with it.

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2 Responses to Meltdown

  1. andyw says:

    Wooh! Once again you’ve saved my bacon. No extra SLA fun for me then….

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