# relay voltage question



## novaal (Oct 1, 2015)

This is my first time working on an electric car, it's currently a 72v system & I want to upgrade it to 96v but it uses a few 72v Bosch style relays to control 12v circuits on the car. 

I can't find Bosch style relays with 96v coils, is it possible to use a resistor to reduce the voltage to the relays to 72v? 

drop 96v to 72v = 24v
relay coil is .160 amps / 75 ohms

resistor would need to be 150 ohms / 4 watts minimum?


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## major (Apr 4, 2008)

novaal said:


> This is my first time working on an electric car, it's currently a 72v system & I want to upgrade it to 96v but it uses a few 72v Bosch style relays to control 12v circuits on the car.
> 
> I can't find Bosch style relays with 96v coils, is it possible to use a resistor to reduce the voltage to the relays to 72v?
> 
> ...


I think you have the coil voltage and contact rating mixed up. 0.16Amps at 75 Ohms is 12V. Usually relays have the coil in the control circuit (12V) and contacts in the high voltage circuit.


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## novaal (Oct 1, 2015)

you're right, I was checking a 12v relay also, mixed up the readings for the example.

The relays do have a 72v coil, the contacts on one control a 72v item, the other two relays contacts control 12v circuits.

I'm not sure if it was possible to use a resistor with the appropriate ohms/watts to lower the voltage to the relay from 96v to 72v & use the original relays.


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## major (Apr 4, 2008)

novaal said:


> you're right, I was checking a 12v relay also, mixed up the readings for the example.
> 
> The relays do have a 72v coil, the contacts on one control a 72v item, the other two relays contacts control 12v circuits.
> 
> I'm not sure if it was possible to use a resistor with the appropriate ohms/watts to lower the voltage to the relay from 96v to 72v & use the original relays.


Yeah, you can do that. The numbers in the first post didn't add up.


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## novaal (Oct 1, 2015)

thanks, that's what I was hoping to hear


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## ysrman (Oct 6, 2015)

Where did you find a 72 volt relay? I am having some trouble finding one for my project.


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## novaal (Oct 1, 2015)

They were factory in the car (a ZAP Xebra), look like regular Bosch 12v ones. All I have found are 12 and 24 volt.



another relay question:

Is it possible to use a resistor the same way on 72v SW200/SW202 style contactors to run them on 96v? They're pulling 260ma so a 100 ohm/10 watt would work? Would be a lot cheaper than replacing all the contactors.


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## ysrman (Oct 6, 2015)

thank you for the reply with your help I was able to find it here http://xebraparts.com/72v-relay.html


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## Roy Von Rogers (Mar 21, 2009)

I have a 2008 Zap PK, and I have upgraded to lithium some years ago to 98v, and have run all components at that voltage with no problems.

The system never goes above 98v. I was more worried about the dc-dc converter, but so far have had no problems, exept its and idiot magnet.

T-boned in right side from old fart texting and running the light, and a few months ago the postman backed in to me.

Roy


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## novaal (Oct 1, 2015)

the 72v contactors work on 96v? That would save me a lot if I don't have to replace them.


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## Roy Von Rogers (Mar 21, 2009)

This was running lithium, the charging voltage was 98v max, the cells drop to about 3.38v per cell, so the running voltage never exceeded 95v.

Now if you are putting in two more 12v agm's, you need to think about the max voltage after charging.

Before I switched to lithium I installed one extra agm, so I ran on 7 agm's with no problems.

Roy


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## novaal (Oct 1, 2015)

They're 12v gels, the 6 currently charge to about 12.8v each, 8 would put the pack to about 103v, probably better off changing the contactors, it's only money


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## Roy Von Rogers (Mar 21, 2009)

novaal said:


> They're 12v gels, the 6 currently charge to about 12.8v each, 8 would put the pack to about 103v, probably better off changing the contactors, it's only money


I'm not too sure what controller you have, but be aware that if its a Curtis, it has a 102v limit, your right on the edge.

I'm not sure about the relays, they may hold up, but I was always worried about the dc-dc converter, more then the relays.

Btw 7 AGM's worked well, but let me tell ya, the lithium's are the way to go, they make an unbelievable difference. The lithiums let me run ypu to 45 at no time, and would go to 50 with no problem.

Btw, you never said what you had, SD or PK.

Roy


Roy


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## novaal (Oct 1, 2015)

It's a purple SD, found it at a swap meet, it was sitting for years & the brakes froze up, the guy who I bought it from couldn't find parts to fix it.

The controller is a Curtis 1221 good to 120v, the DC-DC converter was one of the weak first design 20A units, I found a 40A 96v-12v converter & 96v Delta-Q charger.

I'd like to get lithiums but a little out of my price range for now.

I found a 96v SW202 FWD/REV contactor today, still looking for a pair of 96v SW200 style ones, seem to be unavailable everywhere I've checked.


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