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Discussion Starter #1
Hi all,

I took the prelude for a little drive on Saturday, but first some back story.

The Prelude conversion has a ~18 kWh battery of 70 Ah capacity and 270 V nominal voltage. It will soon be 355 V nominal, but more on that another time. I have a master contactor and a master precharge relay buried inside the battery pack. When I turn the key to ON, a 12 V delay timer was supplied with +12v. The precharge relay closes a 200R resistor across the master contactor 0.5 seconds before the master contactor closes. This mean the HVDC distribution box at the front of the car now has full pack voltage and is able to supply all HV ancillaries. The drive contactor and drive precharge relay are only enabled when the key is turned to IGN and held - after about 4 seconds the drive contactor closes. This is managed by the Greatland inverter.

The TC-Elcon DC/DC converter is supplied from the HVDC distribution box with a 20 A fuse. The converter won't supply +12 V unless the Enable pin is supplied with +12 V, which comes from a fused, switched supply. In this case it comes on when everything else comes on when the key is at ON.

Now I went for a drive down the hill and after stopping at the hardware store I drove on to a friend's house. I'd noticed the 12 V auxiliary voltage getting lower - it was sitting at 11.5 V. This suggested wither the DC/DC converter was dis-enabled, or was faulty. Great.

Anyway, after parking up and visiting a friend, I got back in to drive off - no dice. We pulled off the covers and tested with a multi-meter. Sure enough, we weren't getting pack voltage to the contactor. Towtruck for me...

I pulled the battery out of the car and checked the main fuse - blown. That explains why we weren't moving, but the strange thing is that the fuse was working fine right up until I parked the car. What would cause it to blow just by turning it off (or on)?

Could the DC/DC converter have anything to do with it? It's not permanently connected to the battery pack like many instruction diagrams suggest. If there was an inrush current issue, surely the 20 A fuse protecting it on the HV side would have blown before the 200 A fuse on the main pack did? That particular fuse is just fine.

Curious if anyone here has had main pack fuses blow for inexplicable reasons. I'd briefly take it up to about 240 amps for about 3 seconds, but it spent most of it's short life well under 100 amps. :confused:
 

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Without taking it apart, diagnosis is difficult. Could be a weak fuse, or have fatigued open, used to be common in VW aircooled euro fuses in the dash, and I have had it happen on 3 phase equipment. Pushing them to above rated does tend to warm the fuse link, vibration then kills it. I always carry a harbor fright dvm and a spare fuse.
 

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I did cut the fuse open and it had blown in the true sense of the word. Molten sand and everything.
On the few blown fuses of similar construction which I've cut open, something looks fishy with that burn pattern. Got some better close-ups? Also did your system work after replacement of the fuse?

Regards,

major
 

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Discussion Starter #6
On the few blown fuses of similar construction which I've cut open, something looks fishy with that burn pattern. Got some better close-ups? Also did your system work after replacement of the fuse?

Regards,

major
I'll try and take a picture with something other than a potato camera. But all the perforations are melted as if it blew like it was supposed to.

I have pulled the battery apart for other reasons, but will be able to give an answer by the end of the weekend.

One thing I will say is that this fuse is protecting a circuit which is running at ~270 volts, not the 360 volts it was originally intended for. So the currents are a bit higher than what they should be for the power I'm demanding. Hopefully I'll have all 8 modules installed and we'll be back on 96s. I note that the Mitsubishi iMiEV runs 88s (325 V nominal) and has peaks of 55 kW, but is protected by a 300 A fuse.
 

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Discussion Starter #8 (Edited)
I tried to peel away more of the sand and take a better picture, but every perforation on the fuse had burned out exactly as it was supposed to, so it crumbled away in my hand. It sure didn't look like lots of amps were being passed through at the time because only the perforations were cooked.

I've finished putting the main battery pack back together, but I will be installing the last two modules in the spare wheel well of the Prelude so I have a full 400 V at full charge. I'm hoping the higher voltage means less amps for the same sort of performance, that is, overall average lower currents. After all, 200 A at 355 volts is still 70 kW, which is enough to move a 1100 kg car pretty smartly.

Then I will know if there was anything more sinister at play.
 

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Im no expert,

maybe, due to the extended running in EV mode with the larger capacity battery, the slow burn fuse is working for longer at the limit of its tolerance and just failed over time.

I had it once on a prius plug in conversion with an extended run in ev mode and a heavy accelleration period up a hill.

Anthony.
 

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Discussion Starter #10
An update on this problem -

I finally re-installed the battery and added the last two modules in series. This time the main fuse is outside the main pack, so if it did blow it's a quick repair job (albeit expensive).

I noticed (in a round about way) the drive contactor was stuck. I managed to unstick it by first confirming there was no HV behind it, and powering it on and off a billion times with a power supply. It eventually came loose, but the rear (master) contactor was stuck on too. I powered it on and off a billion times too, remotely, making sure there was nothing in the HV circuit.

Once unstuck, I connected everything back together and it drove and charged just fine.

The charger was replaced with a CAN-controlled one, but frustratingly, the charger ran on a 500 kbps rate, while all other BMS stuff was on 250 kbps. The only remedy for this was to re-program all 8 BMS modules, the current sensor, EVMS and the screen. Thankfully Ian came around to my house to help with this. Seemed a shame to pull apart a working EV for this seemingly minor task, but oh well.

Back together, the rear pack went in. The main power connector was attached, along with all the low voltage stuff. Only after everything was completed under the car did I connect the last two modules in series with the rest of the pack, including a new 200 A fuse. I plugged it in to charge and it gave an error. No charging either way. I tried to engage the drive - nothing. Time to bust out the multimeter again.

Blow me down, the drive contactor was welded again! I managed to unstick it, and decided to check the master contactor - it too was possibly stuck, but in order to check if I had un-stuck it, I put a multimeter on the main HV input to the distribution box. It showed a few millivolts when not powered, and about 14 volts when powered. Suspicious - probably stuck. So I powered it with a separate power supply on and off until it sounded like it was coming unstuck. At this point I realised that the charger and DC/DC converter was still connected at the HVDC end, and figured this could possibly be the source of some capacitive inrush current. I disconnected them and continued to cycle the master contactor - some progress - I was reading about 36 V when it was on... Should be about 400 V...

Wait a minute... check the fuse.

Popped again! Damn! The fuse 200 A was blown, again. At least it was a quick repair, but shit this is getting expensive. I installed a new one - 400 A being the only size I had left. Installed the cables as they were, checked the voltages, all good. Re-connected the charger and DC/DC converter (no sparks) and turned the car on. It started as it should, drove as it should and no errors. Went for a ~10 km drive, came back and plugged it in to charge. Charged as it should all the way up to 400 V.

So it seems the charger is the source of my fuse popping problems?! I'd really need to put a scope on it or something, but it's very strange.
 
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