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Charge battery impossible: Ground resistance exactly 1000 ohm no matter what - help?

1.8K views 8 replies 2 participants last post by  Jeremy Harris  
#1 · (Edited)
Hi

I just purchased a defective Zoe and have fixed numerous problems using online sources.

I think this is the last problem (besides needing to replace two cells in traction battery, perhaps - they are 2.95V while the rest is 3.6x V).

When I try to charge is gives the "Charge impossible" message. Fault code P0668-48 IIRC.
I get a ground fault error. So I tried to connect PE to N and I get main grounded fault. So I tried to charge without earth and with earth and also adding an extra ground pole.

In all cases Zoe reports EXACTLY 1000 ohm ground resistance in Canze.

It seems to me that the 1000 ohm is perhaps the cause of an internal default or because of a lose connection in the measurement circuit?

I also measured from PE on charging socket to GND on battery: 0 Ohm. I checked that CC and CP was not disconnected and they were fine.

Is there anyone who can enlighten me?

Edit: Btw. I tried to charge again and this time it told me check charger stand. No changes to Earth resistance - still 1000.0 Ohm exactly.
 
#2 ·
The Zoe needs a minimum value of Ra of 150 ohm. This means that it will show the "Charging impossible" message if the installation it is trying to charge from has a value of Ra (or Ze) that is above 150 ohms. The only fix is to reduce the impedance of the earth electrode to a low enough value. In some difficult locations this may mean using a buried earth mat or, perhaps, a Condudisc. I've tried the latter once and found that even buried at a shallow depth of about 500mm it reduced Ra over two 1.2m earth rods by around 50%. Easier to install than a copper earth mat, too.
 
#3 ·
Yes - I also understood that - which is why i tried to add one extra earth electrode (ground pole) and shorting PE to N. I could put a 100 ohm resistor between N and PE. What I am wondering is why the Zoe says 1000 ohm no matter the situation?

As I understand it - the zoe injects a positive and then a negative signal into the N (or PE) and uses it to measure the Z / R value.

So I guess it does not want exactly 0 ohm between PE and N - probably 10 ohm or more and neither above 150 Ohm.

It is going to be next step.

But it is the 1000 ohm reporting I am wondering about. Is it just the maximum value it can measure on the Ground? Or something else?
 
#4 ·
Yes - I also understood that - which is why i tried to add one extra earth electrode (ground pole) and shorting PE to N. I could put a 100 ohm resistor between N and PE. What I am wondering is why the Zoe says 1000 ohm no matter the situation?

It is going to be next step.

There are two possible reasons for this. One is that the earth loop resistance test that the Zoe is doing is giving a false result, due to a fault in the car. The other is that the true earth loop resistance of the installation is greater than 1000 ohms.

The easy way to determine which is the issue is to measure the earth loop resistance of the installation. You will need access to either a dedicated earth loop resistance meter or you could just use a standard electricians MFT (multi function tester) in earth loop impedance mode. The latter is a very quick test, and will give you the value of Ze, the earth loop impedance, and to all intents and purposes you can take this as being very close to the value of Ra (the earth loop resistance).

I'd first try and eliminate the possibility of the installation being at fault, simply because that's pretty easy to do. Once you are sure that the value of Ra is below 150 ohms (which may well be a bit of a challenge for some soil conditions, like sand or rocky ground) then you know for sure that the problem has to be with the car. I'm not a Zoe expert (I know enough to be dangerous just because my wife has a Zoe!) so can't suggest which module in the car does the earth loop resistance test, but my guess would be that it has to be in the front end of the charging control circuitry.

If you lived closer you'd be welcome to borrow my MFT and check the installation, it'd only take a couple of minutes. Perhaps you can get a local electrician to check this, it's a very quick and easy test to do.
 
#8 ·
Final update: I installed a new ground electrode (2½ meters into the ground).

It gave me a 30 ohm resistance to Earth.

Zoe started charging.

It stood at 0% for a while and then started to rapidly increase.

I suspect I will have to change a pair of cells that were at 2.95V when I started charging. They increased very quickly and are almost at par with the others now at 50% charge. My calculations show that the 68% fits with its own estimates so far - but lets see...

I am using CanZe App to readout BMS codes: One of them says "BF". I dont know what i means. And it comes and goes.