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"PreCharge Failure"

slapshot0130

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May 29, 2020
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Running into the issue of the "precharge failure" with the ANT BMS.

I think its due to a cell difference issue, causing the BMS to disconnect from the system. Once this occurs, the BMS will not auto-reconnect when the cells are in balance, due to the precharge failure, unless I disconnect the negative and reconnect to the system, where the inverter will charge its capacitors again. I have been trying to get the BMS to auto-balance but any setting I use, just doesn't seem to get the BMS to balance.

About a month ago this issue would occur near the top of the charging cycle so I just reduced the top voltage, but now the BMS is disconnecting when the battery is not charging and under a lite load, just powering a fridge.

Any thoughts would be helpful, currently trying to bottom balance again to see if that works.
 
I am not sure what "Precharge Failure" means but....

1) The Ant BMS appears to have an extra FET to pre-charge the capacitors on the inverter before it turns 'full on'. I am guessing that it attempted to do the pre-charge but did not see the voltage on the output go up.

2) The pre-charge failure may be a second order effect where something else made the BMS shut off and the pre-charge failure is happening when the BMS tries to turn back on.

3) I see that you have the extra cell wires bundled and hanging off the BMS. I don't know if it matters but you should tape over each end so they can't touch each other.
 
So I have the ANT BMS also; 300a version of the one Will reviewed.
Anyway it's been working fine last 24 hours or so. I decided to slap on the heat shrink that came with it for the temperature probes.
I thought, "hey this will be a fun test to see if it disconnects when things get hot".
So I did my thing, it disconnected, bravo.
Now, no matter what I do, I get this same error as you mention "precharge failure"
It will not reconnect the battery.
I disconnected it, waited a few minutes, reconnected it, did a factory reset, etc. alas the error remains.
Did you do anything special to clear yours other than disconnecting the batt. neg?
I tried that and the factory reset (and a reboot) from the app.
 
I am not sure what "Precharge Failure" means but....

1) The Ant BMS appears to have an extra FET to pre-charge the capacitors on the inverter before it turns 'full on'. I am guessing that it attempted to do the pre-charge but did not see the voltage on the output go up.

2) The pre-charge failure may be a second order effect where something else made the BMS shut off and the pre-charge failure is happening when the BMS tries to turn back on.

3) I see that you have the extra cell wires bundled and hanging off the BMS. I don't know if it matters but you should tape over each end so they can't touch each other.
I think it has to deal with number one on the list. I'm just perplexed on why it shuts off in the first place. The logs say discharge(0)celldiffhigh, and when I look, they are perfectly balanced.
 
So I have the ANT BMS also; 300a version of the one Will reviewed.
Anyway it's been working fine last 24 hours or so. I decided to slap on the heat shrink that came with it for the temperature probes.
I thought, "hey this will be a fun test to see if it disconnects when things get hot".
So I did my thing, it disconnected, bravo.
Now, no matter what I do, I get this same error as you mention "precharge failure"
It will not reconnect the battery.
I disconnected it, waited a few minutes, reconnected it, did a factory reset, etc. alas the error remains.
Did you do anything special to clear yours other than disconnecting the batt. neg?
I tried that and the factory reset (and a reboot) from the app.
I didn't have to do anything else. I just have to disconnect from the negative, the recharge error goes away. Then I reconnect, spark occurs from inverter capacitors and it's back to working.

I just had things running for five days straight, and last evening with no changes to the system, recharge failure with the error <discharge>(0)celldiffhigh, even though they were not.
 
I didn't have to do anything else. I just have to disconnect from the negative, the recharge error goes away. Then I reconnect, spark occurs from inverter capacitors and it's back to working.

I just had things running for five days straight, and last evening with no changes to the system, recharge failure with the error <discharge>(0)celldiffhigh, even though they were not.

<discharge>(0)celldiffhigh must mean that the BMS thinks the difference between cell voltage is too high. Since the cells are fine when you check, the cells are probably not the problem. That leaves the wiring or the BMS.

Here are a few things to try:

* With a reasonably high load on the system, check the cell voltages. Do any of them seem to be way out from the others? If so, concentrate on that cell for the following steps.

* Visually inspect all of the wiring and bus bars and make sure everything is tightened down well. A bad (resistive) connection can cause strange behavior.

* Take all the bus bars and wiring off, make sure everything is clean and put it back together. (I once had a cell with crud on a terminal pad that created a resistive connection. It caused the BMS to occasionally shut down with a low cell voltage... but only sometimes and only under load. It was a real PITA to figure out.
 
I didn't have to do anything else. I just have to disconnect from the negative, the recharge error goes away. Then I reconnect, spark occurs from inverter capacitors and it's back to working.

I just had things running for five days straight, and last evening with no changes to the system, recharge failure with the error <discharge>(0)celldiffhigh, even though they were not.

There is a setting in the BMS where the user can customize what constitutes "too high" in differences between the cells.
You might want to try messing with that; increase it substantially for the test. Make sure to click <set> and then <save>
If still no difference I'd click <reboot> after that. my bad if you tried this already but I thought I should mention it.
 
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