Bluebird Precharge issue

Conversion summary

Nissan Leaf Motor, Inverter and Transmission from 2016 30kWh model

Batteries – New 40kWh leaf modules – 8 in from case 16 in rear case

Leaf PDM now contains – Thunderstruck VCU, TC DC/DC converter, 12v fuse & relay boxes, 50a/750v Contractor for 3KW PTC heater element (not pictured as in lower section) – See picture below summary

Orion 2 BMS (in rear battery case)

TC 6.6kW charger (in rear battery case)

3kw PTC heater element in place of original in dash

Two 400a / 750v high voltage contactors in rear box – 1 Negative 1 Positive

50a / 750v Contactor for precharge circuit in rear battery box

2 x HS100 30R F Pre charge resistors wired in series in rear battery box

Precharge issue

HV System designed and installed by Jay Derrett from Powerdrive EV (who have now closed down)

He didn’t supply detailed wiring diagram but we have got this from him

Having had an issue with the DCDC in one of his previous build bhe put a 5 second delay relay on the DCDC converter to stop it drawing current during precharge – it draws around 1 amp

Conversion complete Early Dec and functioned correctly from the start.

Issue started when doing range testing – The car blows up pre charge resistors, and has done so 3 times

First time – had been driven continuously with heater on for over 90 minutes – left off and standing for 10 minutes and when turned back on again (heater switched on) it blew up the 1 x HS100 30R resistor fitted. We didn’t note battery SOC but guess it was around 50%.

Second time – 1 x HS100 30R resistor replaced and had been driven continuously with heater on for over 120 minutes – left off & standing for 10 minutes and when turned back (heater on) on it blew the resistor again (this time not a physical blow up – more a fizzled burn out)

3rd time – Zero-EV advised that 2 resistors needed to be fitted but it was too close to Christmas to get them so we fitted a use Nissan Leaf OEM one. We also fitted an 8 second delay relay to the heater. Again driven continuously for around 45 minutes with heater on then switched off and when turned back on again 10 minutes (with heater switch on) later the resister burned out.

4th Issue 30.12.21 & 31.12.21 – Having now fitted 2 x HS100 30R resistors in series we started range testing again with a fully charged battery, over a couple of days and car was fine until later in the day on 31.12. I had driven the car 34 miles in the morning then 2 and half hours later drove it 7 miles before turning it off. This time luckily the heater was switched off (it had been on and off whilst driving) when I parked up and during subsequent attempts to start up.

When I went to start the car again (at 16.17) it would not activate the second contractor but no sign of resistor blow up (no sound, smoke or smell). I went to plug in the laptop to the BMS whilst the ignition switch was still on and after a long wait the send contractor clicked in.

I then took video of the length of time it took to active the second contractor 3 times and got 34 seconds, 23 seconds and 47 seconds (videos of this below)

Data of test driving, SOC, Battery temp (as shown by BMS) and pack voltage

(Driven continuously between the two times shown with heater on most of the time)

TimeTrip MilesSOC %VoltsTemp ave C

Video of start up

We have developed a board to take the SOC from the Orion BMS and show SOC not he original file gauge. When ignition switch is off needle shows around half then moves slightly when it gets ignition live then again to show the SOC when the second contractor is activated)

Normal – takes around 6 seconds (car was at 34% SOC and had stood over night)

31.12.21 16:20 – takes around 34 seconds

31.12.21 16.22 – takes around 23 seconds

31.12.21 16.23 – takes around 47 seconds

VCU Settings

Conclusion 03.01.22

I initially thought the pre charge minimum had been set too high in the VCU but this doesnt look to be the case.

Whilst testing I regularly photo the BMS live data screen. The videos shown on this page were taken when the pack was showing around 34% SOC which was 341v.

I dont know why the precharge is taking so long sometimes but think that the resistors blowing up was caused by the heater coming on before the precharge routine had finished.

Is it possible to us the contractor enable feed from the VCU to power the turning on of the DC/DC and the Heater? That way they cant be on before pre charge is complete (we will leave the 5 & 8 second delays built in also for extra protection)

Any input on the cause of this is highly appreciated.

We are now bringing the design and installation of the High Voltage systems in-house for future builds to ensure we have the knowledge to solve these issues.

Update 04.01.22

Came to work on the car today and the 12v battery is flat (not the first time this has happened) – checked all vehicle lights etc and none left on. Recharging battery and decided to carry out some tests.

Precharge output from the VCU

We found that this is at 12v when the vehicle is turned off – it goes to zero once the main contractor is enabled by the VCU. Due to this we tested the 12v inputs to the precharge and contactors and got the following results. We also tested that the VCU is being powered by switched live to both of its inputs and it is.

The contactors are fed via a 6 pin multi plug which is shown in the below pictures.

When tested we found the following

PinIgnition off VIgnition on V

Rough Diagram



Pin 3 on the plug (Charge Enable) goes to both the negative on the precharge contractor and black wire input on the Negative contractor

Should the precharge circuit be showing 12v when the car is off? Could this be causing the issue with the blow resistors?

If the precharge should not have the 12v feed when off how can we rewire things so it does not?

Update 6.01.22

I think I may have found the (or an) issue – it looks to me that the Precharge contractor and negative contractor are sharing the feed from the Charge enable BMS wire (Grey wire) and the Positive contractor is getting the feed from the Discharge enable BMS wire (Blue/White) which is not how it is marked on the Precharge diagram provided by Powerdrive.

NOTE 1 We are getting no response at all from questions to Jay at Powerdrive hence having to try and figure this out ourselves

NOTE 2 We have Stopped the Heater coming on before precharge is complete by only allowing the switch to work once it has a signal from the VCU contractor wire. This way the heater cant draw its 17 amps until the prechage sequence has finished

Question – if Im correct how would this effect things

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