openinverter forum

Hello,

I assumed I could use regular coolant hose from my local auto parts shop in my EV conversion. But then I came across some comments on diyelectriccar that said that you need to use special non-conductive coolant hoses.

So now I'm a bit nervous. So, for the record (and for anyone who asks this question in the future), what sort of coolant hoses can I use for a typical EV conversion - say, a 350v nominal battery paired with a Nissan leaf stack?

Does the material matter? Rubber/silicone?

Is there some sort of conductivity specification I can look for?

Am I overthinking this and can I use any automative grade coolant hose?

Thanks in advance.

The "box" of all of these high voltage things should be grounded. The battery cooling apparatus should also be chassis grounded. You should use non conductive coolant if it goes into the battery area (and to help galvanic corrosion).

I don't see non conductive hoses helping with anything except a leaky battery or other hv item that fails an isolation monitor test to the box. But that means the battery box is also not grounded to the chassis.

You could use silicone hoses if you're worried but I'm not seeing the why or the worry unless grounding to chassis is skipped. I don't mean hv - or mid pack to chassis, I mean all hv component "boxes". All boxes should be chassis grounded to prevent high voltage islands if an isolation issue happens.

Scrappyjoe wrote: ↑Tue Jan 20, 2026 7:51 am Hello,

I assumed I could use regular coolant hose from my local auto parts shop in my EV conversion. But then I came across some comments on diyelectriccar that said that you need to use special non-conductive coolant hoses.

So now I'm a bit nervous. So, for the record (and for anyone who asks this question in the future), what sort of coolant hoses can I use for a typical EV conversion - say, a 350v nominal battery paired with a Nissan leaf stack?

Does the material matter? Rubber/silicone?
.....

I think you are overthinking it... its not like 800Vdc or more...

I like to take used rubber hoses from various cars. For the radiator hoses which is 32mm i order Fiat 500 radiator hoses and then i make 32mm to 19mm adapter soldered out of copper pipes.

Sometimes i also use 18mm copper tubing just because it is easier to get straight tubing to fit under the car than rubber hoses.
https://mazdamx3ev.wordpress.com/2023/1 ... ng-piping/

Scrappyjoe wrote: ↑Tue Jan 20, 2026 7:51 am But then I came across some comments on diyelectriccar that said that you need to use special non-conductive coolant hoses.

Sounds like BS to me. Even if the was a fault, where is the electric potential going to come from?
Usually hose barbs are on metal cases and the metal cases are grounded. If you're grounded on both sides, there can't be no electric potential between them, hence no voltage.

Well that settles that then. Thanks for the input everyone! I will proceed without fear then.

Yea, if the coolant becomes charged, so is the WHOLE VEHICLE! Also, since EV "coolant" never ever gets to anything close to it's boiling temperature, a pressure cap and super tight joints that would survive elevated pressure are total overkill.

OK, so to summarise what I have read above:

1. Don't worry about the hoses.
2. Use non conductive coolant
3. Make sure all HV components are grounded.

3 is important because any HV 'leak' is going to either come from the cables or from an HV component. Grounded HV components will trigger isolation failure if there is an HV leak, resulting in the contactors opening. Possibly also my ECU or components frying, but that's fine I'd rather lose an ECU than end up in the ER.

Scrappyjoe wrote: ↑Wed Jan 21, 2026 5:43 am ....
3. Make sure all HV components are grounded.
....

If you take care of the no. 3 you will also have less EMI problems.

Also dont forget to install bleeder valves on ALL higher points in your installation to release trapped air.

Question: What device are you using to check for an isolation fault?

You need to monitor both the HV DC and AC sides to be "safe".

I took jrbe’s comment to mean that you don’t need a discrete device for this. If you have grounded all the devices that have HV passing through them, then if there is HV leakage, it has to pass through those devices physical housings to get anywhere. And in doing so it’ll short the 12v ground, resulting in your 12v system immediately short circuiting, opening the contactors.

Scrappyjoe wrote: ↑Thu Jan 22, 2026 8:23 am I took jrbe’s comment to mean that you don’t need a discrete device for this. If you have grounded all the devices that have HV passing through them, then if there is HV leakage, it has to pass through those devices physical housings to get anywhere.

There's a big difference between an isolation fault and a short. Think of it as the difference between a 1megohm and a .1 ohm resistor.
Your ground strap / connection has a resistance too, so the isolation fault resistance and the ground connection can be looked at like a voltage divider.
An isolation monitor checks how much of a fault / resistance there is high voltage + or - to ground to make sure there's no fault condition. Some people (a lot of people?) skip this piece when doing swaps and rely on the grounding to keep them safe. If the ground connection fails along with an isolation fault you now have a potential high voltage island. The isolation monitor should open the contactors if there is a fault (when it's safe to, thanks muehlpower), helping to prevent the possibility of a high voltage island staying powered up.

And knowing there's an isolation fault helps you be / think a bit safer when investigating the issue. Power ends up where it shouldn't be. When it's not 0 or low voltage it will be dangerous to work on. Treat high voltage DC as if it will kill you if it gets the chance. And if there's an isolation fault treat it as anything you touch will be high voltage.

ZooKeeper wrote: ↑Thu Jan 22, 2026 2:20 am Question: What device are you using to check for an isolation fault?

You need to monitor both the HV DC and AC sides to be "safe".

I use ZEVA BMS EVMS3 connection to gnd for that. It can display % of isolation.... I am not sure if it is totally legit but it showed drop in isolation with exposed HV contacts in bad weather.

In Germany, and presumably throughout the EU, a minimum insulation resistance of 500 ohms/V is required. Monitoring is recommended but not mandatory. Insulation monitors from Bender or, soon, an ISA shunt with integrated insulation monitoring are available for monitoring purposes. Immediate shutdown in the event of a fault is not common practice, as this can lead to hazards due to sudden loss of drive power and further damage. The driver is informed as normal and, if necessary, starting is prevented. The coolant and hoses should play a minor role here, as they are not in contact with live parts. I use GLYSANTIN G48 as antifreeze because it is approved by Tesla, as I have mainly installed Tesla components.

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