Paul & Sabrina's cheap DIY 144v motor controller

[duncan]

Hi Paul

One of my friends lent me a Soliton - bye its a big bugger!

I spent today installing it - unfortunately when I finished the installation and tested it I found that my 44S 2P Headway battery pack had gone high resistance

I can check cells in fours (2S 2P) - all at 6.65v - except one -3.33v -oops

I think I have lost a pair of cells, they seem to have died when the controller blew

It's 10pm and I need to remove most of my electrics before I can lift out the battery pack - so tomorrow's drag race is orf
I will still be going as I am doing the traffic management

[duncan]

Hi Paul

could I have knackered the capacitors in my controller by discharging them after use?
The car had been sitting for about 10 days with discharged capacitors

This is a quote from Tesseract on the DIY Electric Car forum

That is only true for aluminum electrolytic capacitors; for any other kind it doesn't matter whether you leave them charged or discharged.

More specifically, the leakage current through an "elko" increases the longer it is left discharged, and this current, if abnormally high, can result in the capacitor overheating internally. The cure for this is to bring the voltage up slowly on any caps that have been stored/unused for an extended period of time (weeks? months?), as this allows the dielectric oxide layer to reform gradually and limits heating from leakage current to a rate that the capacitor can withstand.

What is the recommended way to break pack voltage? - DIY Electric Car Forums

I have my pack apart - one cell had failed giving me a 43S 2P pack + 1S
The one S had had to pass the same current as the remaining pairs and had blown its terminal off

[mrbigh]

Originally Posted by duncan

I have my pack apart - one cell had failed giving me a 43S 2P pack + 1S
The one S had had to pass the same current as the remaining pairs and had blown its terminal off

OUCH!!!! that it's not nice...........

[MPaulHolmes]

Sorry Duncan, my internet connection is a friggen pile of crap. At least it's really really expensive, so that makes it all OK. haha. (one of the benefits of living in the middle of nowhere.)

I don't think the capacitors sitting for 10 days would cause any problems. But you should definitely use a precharge resistor when filling them up. Could you take pictures of the inside of the controller? Specifically, the holes through the control board where the M- bus bar is? You say you had replaced the mosfets before? Were the mosfets all you had replaced?

[duncan]

Hi Paul
I just lost the post I had written!

Anyway - the story
A MOSFET blew on first start up with the main pack - I noticed the pop and smoke but the car drove OK so I thought that I had zapped a passing spider

I realized my error when I checked resistances to earth
I replaced the blown MOSFET and its neighbor which appeared to be cracked

At that stage the car was going well - easy 100Kph on its certification test and good acceleration

I left it sitting for about 10 days

First switch - one contactor and 12v for controller
Precharge - I am using a halogen bulb, this normally glows for a few seconds and goes out
On this occasion it stayed on
What I should have done was shut down and taken it apart
What I did do was switch on the second contactor
BANG - SMOKE - OOOPS

The blowup took out all of the MOSFETS and one of my cells

[dave koller]

Originally Posted by MPaulHolmes

Sorry Duncan, my internet connection is a friggen pile of crap.

HaHA Welcome to MY world on dial-up (no there is no DSL) but I am working on something. heh heh !

[duncan]

Hi Paul

I have started desoldering the blown MOSFETS from the power board

Its nerffed - the copper islands are coming loose - looks like I will need to buy a new power board and components

My car is back together with a battery bridge to find battery problems and a borrowed Soliton
But I'm still waiting for my certification plate!
Apparently being a "scratch built" and an EV together has slowed the approval process

[MPaulHolmes]

Ya, the milled pcb had some issues. It's not as reliable as the power board from an actual pcb house, with the solder mask. The problem is, the new power board has only 3 holes for M-, and the bus bar pads are 5/8" instead of the previous 3/4". It's not very compatible.

You don't need the copper islands. You only need to solder the mosfet gate leg directly to a gate resistor. You could just feed the resistor leg through the tiny hole, and then solder them together. But it's concerning why they are blowing up in the first place. For some reason, before they had blown up, at least one had failed shorted. I would also replace the MIC4451 (the driver on the control board).

[duncan]

Hi Paul
I will take the blown MOSFETS off the board and clean it up
I am worried because each time I do something it moves further from its initial condition

Like it's been through the wars

I have learned a lot about soldering and electronics from this project
So I would probably feel happier about starting again

I expect that I would be able to produce a more workmanlike product

With that in mind - where are you on the bigger controller - 1000amp? - I had always intended to upgrade at some time - now would seem to be a good time!

I will clean up the MOSFET mess,
Desolder the control board where the connections to the power board go in

I am nervous about desoldering and replacing the MIC445 - the control board represents a small part of the total cost - and the finer soldering requirements!

[duncan]

Hi Paul

Taken the MOSFETs off - it's a mess, the blowup has done a number on the board