Prelude conversion project - some questions

[jonescg]

I took Roe Highway home today to check the car's energy consumption on the freeway. At 100 km/h it averages 13.5 kW
If there is a slight incline, you might see 20 kW, but it soon drops to under 10 kW as you crest the hill.
So on net flat ground, the electric Prelude has a highway speed range of about 160 km! I am impressed.

[francisco.shi]

That is really good. That is 135wh/km which is almost the same as the factory made electric cars for that size.

[jonescg]

Yeah I am very impressed. It seems to hold about 95 km/h in 4th gear, top speed. This is no doubt a controller setting which I hope to change on Monday. Otherwise 5th gear is fine, and has a top speed of about 110 km/h I guess. No need to exceed 100 most of the time. It seems in stop-start traffic the economy isn't much better, but who willingly drives at 60 km/h for hours and hours?

[brendon_m]

So 5th gear currently has a limit of 110kmh? Is that an rpm limit or a constant power limit?

[jonescg]

I think the motor is speed limited. Rod Dilkes will be coming around on Monday night to mess with the settings a bit. It would be nice to have more torque than its current settings, as taking off in 3rd is a bit sluggish and 4th is way too slow for most circumstances. We also need to bump the regen voltage up to 395 V or so. It's currently set to 360 V as the regen only works when the battery is below 50% SOC. Not that it affords much regen - about 7 kW at best.

[jonescg]

New coilovers fitted - the car drives like a dream They are set to give about 140 mm of clearance all round, but still offer good damping over some of the usual bumps. Getting harder and harder to hand this car over!

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However I noticed when turning the car on it would still give a contactor error, and when turning the key I never heard the main drive contactor click... but it still drove OK.
Ipso facto, the drive contactor is welded, again. Not knowing if the master contactor in the back was also welded, I carefully disconnected the negative supply to the HVDC box. I then disconnected the 12 V supply to the contactor and power cycled it. It dropped out fairly quickly. Once I knew it was open I checked the potential on the battery side of the contactor and got a fairly nebulous 11 volts. So it's not fully open, but I can see this being a problem down the track. Might be time to ditch the rear contactor and install a manual isolation switch?

[brendon_m]

Is it a new contactor or old or did you get the upgraded gigavac already? My experience is if contacts weld once they'll be very prone to weld again and again.

[jonescg]

Is it a new contactor or old or did you get the upgraded gigavac already? My experience is if contacts weld once they'll be very prone to weld again and again.

It was new once But yeah, this one has welded several times now. I wouldn't mind getting one of these GV350 units, but it looks like they need a separate economiser circuit? Otherwise a GV240 looks suitable. Main thing is the auxiliary leads for informing you of a stuck contactor.

[T1 Terry]

Is it a new contactor or old or did you get the upgraded gigavac already? My experience is if contacts weld once they'll be very prone to weld again and again.

It was new once But yeah, this one has welded several times now. I wouldn't mind getting one of these GV350 units, but it looks like they need a separate economiser circuit? Otherwise a GV240 looks suitable. Main thing is the auxiliary leads for informing you of a stuck contactor.

I had a look through the stock cupboard and unfortunately we only have a 24v contactor with the aux leads. Maybe a voltage booster board to power the contactor if you system is all 12v?

T1 Terry

The Gigavac has a part number of GX14CAB, so the 350 amp continuous model.

[antiscab]

I had a look through the stock cupboard and unfortunately we only have a 24v contactor with the aux leads. Maybe a voltage booster board to power the contactor if you system is all 12v?

I wonder if the hold voltage is 12v or below
if so, a cap and a double pole relay could be built cheaply and reliably to create 24v for turn on, then 12v for running. even more efficient that the normal resistor and cap method

[T1 Terry]

I can investigate that tomorrow, if I remember that is but a momentary pulse of 24v to pull it in with a 12v continuous supply would verify if that was the case. I still have quite a few 24v Gigavacs without the aux wires that I could still use if that is the case. I went back to 12v supply for my control boxes after a few issues with the timer boards on 24v. It seems they can handle 24v but not the 28v at the end of charge.

T1 Terry

[coulomb]

if so, a cap and a double pole relay could be built cheaply and reliably to create 24v for turn on, then 12v for running.

Surely there is an arrangement with some diodes and a capacitor that could eliminate the relay. You do need a push-pull inverter capable of coil current however, and your drive signal also needs to be push-pull (and capable of driving the coil, obviously).

When the input is low, the capacitor charges up via the inverter output and the coil. When the input goes high, the capacitor goes in series with the coil, giving it 24ish volts for a while. When the capacitor discharges, the diode across it takes over, so the coil sees the input voltage less a little. When the input goes low again, there will be a pulse of reverse current through the coil, but only long enough to charge the capacitor. From then on, it just sees the leakage current of the capacitor, which would be negligible. And of course, when the car is off, the whole circuit would lose power and draw no current at all.

[jonescg]

Well the aircon compressor is likely to be installed at some point this week. I'm wondering what the best approach here is - I think I will need to install a better quality master contactor precharge delay timer for a start, but the risk of a master contactor sticking is pretty real.

[francisco.shi]

I think there must be some capacitor that needs to be precharged. The master contactor should only switch under load in a fault condition.
Have you tried to put a precharge resistor and checked that it is not trying to switched into a discharged capacitor?

[jonescg]

I think there must be some capacitor that needs to be precharged. The master contactor should only switch under load in a fault condition.
Have you tried to put a precharge resistor and checked that it is not trying to switched into a discharged capacitor?

Yes, that's why I installed one, and it's own relay. But I also don't want to keep everything pre-charged when the car is off. Hence i need a 0.5 second delay between the master precharge relay and the master contactor closing, so it can manage any capacitance due to the charger, DC/DC converter and the aircon compressor.

I had an e-bay job which worked great for a little while, but it eventually failed.

[T1 Terry]

Is it a new contactor or old or did you get the upgraded gigavac already? My experience is if contacts weld once they'll be very prone to weld again and again.

It was new once But yeah, this one has welded several times now. I wouldn't mind getting one of these GV350 units, but it looks like they need a separate economiser circuit? Otherwise a GV240 looks suitable. Main thing is the auxiliary leads for informing you of a stuck contactor.

I had a look through the stock cupboard and unfortunately we only have a 24v contactor with the aux leads. Maybe a voltage booster board to power the contactor if you system is all 12v?

T1 Terry

The Gigavac has a part number of GX14CAB, so the 350 amp continuous model.

I found a second one if anyone needs one.

T1 Terry

[antiscab]

Hence i need a 0.5 second delay between the master precharge relay and the master contactor closing,

Is 0.5 seconds enough?

I use a 60W light bulb for manual pre-charging a Vectrix, and 0.5 seconds is borderline in that application. that's with ceramic caps with nearly no capacitance too, although there is ~15mA of draw from the dc-dc and cycle analyst

[antiscab]

a smart pre-charger that only closes the master contactor when the voltage gets within a pre-determined level would also prevent welding situations where say the dc-dc is drawing more than normal on start up.
Fixed time pre-charging doesn't guarantee pre-charge unless everything is okay

[brendon_m]

a smart pre-charger that only closes the master contactor when the voltage gets within a pre-determined level would also prevent welding situations where say the dc-dc is drawing more than normal on start up.
Fixed time pre-charging doesn't guarantee pre-charge unless everything is okay

I had a problem when the precharge never reached a close enough voltage after the car sat and wouldn't close the main contacts. I tried adding more resistors but I just couldn't get the voltage to come up.
Turns out when I did some work on the car I accidentally reconnected the dcdc to after the main contactor as opposed to being permanently trickle charging the 12v battery. So when the 12v battery was low, the dcdc drew a lot and the precharge couldn't keep up with the load of the dcdc.
If it was a timed precharge I probably never would have noticed until the contactor kick the bucket.

[jonescg]

Hmmm, time to see Ian again.

[coulomb]

Personally, I don't like to see permanent traction battery voltage in an unattended vehicle. I would prefer to see ELV segmentation, which I think of as <120 VDC, except when the car is on, and with a special exception for periodically re-charging the auxiliary battery when needed. Even then, there should be a visual warning in the engine bay that some cables are live.

I agree with Matt's comments re ½ second pre-charge time not necessarily being enough. It's always best to verify that the capacitors have reached a high enough voltage before enabling the main contactor. You might have to disable the DC-DC converter during pre-charge so that the capacitors can nearly fully charge by the end of the pre-charge period.

I note that the charger output may also have to be pre-charged (though if you do, then the Elcon/TC chargers have lost one of their best features). Maybe this has been the start of your problems.

[ Edit: added "traction" ]

[jonescg]

I'm not so sure that the DC/DC converter or the TC charger is to blame here. I have been successfully charging and driving the Prelude without a properly functioning master contactor precharge circuit. At least a dozen on-off-charge-off cycles. The minitactor and Gigavac GX14 contactor inside the battery pack are switched on at the same time whenever the car is switched on, or plugged in. I haven't had any welding issues since I replaced the fuse and unstuck the drive contactor. The problem with a stuck contactor when you have a couple of them in series, is that if one is stuck and you don't notice, it's a matter of time before you have two of them stuck. I wonder if there wasn't some blip that caused the drive contactor to close without precharge, which in turn caused trouble at the master contactor end?

I have ordered another delay timer to replace the dead one. I think we'll need it for the A/C compressor. The manual mentions precharge, so it's probably fairly significant - certainly enough to weld a contactor which has already been stuck once or twice before.

[jonescg]

I had a chat with the Aircon guy and he seemed to think the current condensor might not be up to the task of both cooling the cabin and keeping the battery cool. The compressor is probably powerful enough, and the blower evaporator is fairly small (can be set to the lowest blower setting) but the battery heat exchanger is pretty huge and will turn refrigerant into a warm gas in no time. Wonder what my options are now? Series probably makes sense if I can't fit a bigger condensor, or alternatively, set up a series of complicated three-way valves for skipping the cabin evaporator completely? Sounds expensive...

[antiscab]

what about a second aircon compressor and condensor?

[jonescg]

car-ac-mcgyver.jpg (61.3 KiB) Viewed 1868 times

I'm sure something can be arranged.