# MES-DEA fluid heater not Isolated



## Lordwacky (Jan 28, 2009)

Hi guys,

I just made an interesting/disturbing discovery regarding the MES DEA fluid heater. 

When testing my pack isolation yesterday I discovered that there was a measurable potential between the my pack positive terminal and my chassis. I was surprised because I was very careful to insure pack isolation during my build and tested for isolation multiple time during my build process.

After testing various system components that had connections to both the HV and 12V systems (BMS, Hairball etc) I discovered that it was the Fluid heater that was providing the electrical connection. When the Fluid heater is plugged into the HV there is a measurable potential of ~125VDC (I have an 156VDC nominal pack). When the heater is disconnected from the HV there is no measureable potential between the HV and chassis.

The Potential is present even when the 12V connection to the fluid pump and the 12V control signal to the fluid heater has been removed. What I assume is happening is that the Battery negative is tied directly to the negative terminal of the heating element in the fluid heater and fluid in the heater and heater core provides and electrical path effectively grounding the HV negative to the chassis.

Obviously this is disturbing so I tested this connection with my DMM and there was only ~ 4mA pulled through the DMM when the positive HV terminal was shorted to the Chassis. So safety wise this doesn’t appear to be a major issue. None the less it is a little disturbing that a High quality (highly priced, anyway) piece of EV specific equipment would have this “flaw”. 

There are a few other Fluid heaters on the market now and it stands to reason that they may also have this flaw. I would recommend anyone that uses a fluid heater to test for HV pack isolation with your heating system filled. I would also recommend that anyone who uses a fluid heater disconnect your fluid heater prior to performing any service to your battery pack.


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## brainzel (Jun 15, 2009)

Thank you wacky.
I use a MES DEA RM4 and will check it, as soon as I got everything wired up again.

An isolated DC/DC converter 12V/12V to the heater should fix the problem i guess.
Perhaps someone could give a reply to this.


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## Roy Von Rogers (Mar 21, 2009)

Try putting a small load across your potential, it may be that the meter is reading across the fluid. I would think that the element would be a calrod type and shouldnt read in to fluid, but I dont know what type of element its using.

Roy


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## Lordwacky (Jan 28, 2009)

brainzel said:


> Thank you wacky.
> I use a MES DEA RM4 and will check it, as soon as I got everything wired up again.
> 
> An isolated DC/DC converter 12V/12V to the heater should fix the problem i guess.
> Perhaps someone could give a reply to this.


As I said in my original post. The potential is present even when the all the 12V connections to the RM4 have been removed. That being the case an isolated DC/DC converter (which I have in place) will not help this situation.


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## Lordwacky (Jan 28, 2009)

Roy Von Rogers said:


> Try putting a small load across your potential, it may be that the meter is reading across the fluid. I would think that the element would be a calrod type and shouldnt read in to fluid, but I dont know what type of element its using.
> 
> Roy


Yeah as I said, I shorted the positive HV terminal to the Chassis through my DMM set to read mA. It only measured ~4mA so there is a very high impedance path from the RM4 to chassis, so it isn't super big issue. I also tried this with my 12V test light, there was not enough current to even light the light. However I was able to see a small arc from the tip of my test light when I grounded it to the chassis.

I agree I beleive the path to chassis is through the heating element --> fluid --> heater core --> chassis. 
I'm not sure what a calrod is, when I looked inside the RM4 when I first got it the heating element was a typical silver metalic color if that means anything.


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## Roy Von Rogers (Mar 21, 2009)

I'm sorry, a calrod element is the type you see in an electic range/oven. 

Roy


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## Tesseract (Sep 27, 2008)

Lordwacky said:


> Yeah as I said, I shorted the positive HV terminal to the Chassis through my DMM set to read mA. It only measured ~4mA so there is a very high impedance path from the RM4 to chassis, so it isn't super big issue.


That's the equivalent of about 39k, which is alarmingly low in my opinion. I wouldn't want to see less than 1M from the HVDC terminals to the chassis ground. How about disconnect the HV connections from the RM4 then measure the resistance between them and the chassis - if it's about 39k then you know the leakage path is inside the RM4; if it is suddenly back up in the megohms then you need to start cleaning battery terminals... 

I think the guys next door to us at Rebirth Auto have an RM4 installed in the Jaguar XK8 they are converting. I can maybe do the same check on it tomorrow.


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