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kabyak avatar image
kabyak asked

Low battery shutdown recovery

My search failed to find a thread on this. On my boat I have: 5 100Ah Victron LifePo batteries, a Smart BMS, Multiplus 3000, BM702 monitor, Cerbo GX, and Battery Protect relays for charging and loads. Also, I have a Wakespeed 500 alternator regulator linked to the BMS. I've had several occasions of loss of shore power causing the batteries to run down to BMS cutoff voltage. This happened again and I found battery voltage at 7.6V, much lower than past events. and well below cutout setting of 12.2V. Why this could be so it one mystery, but the larger question is recovery.

To recover I tried closing the normally open switch linking the generator start battery, this began lifting the house bank voltage. As V gain slowed I started the gen to keep it's battery up. This began an hours long process to raise the LifePO as the rate of voltage rise was about 0.1 V per 45 minutes due to limited current available. At 11.8 V the alarm cleared and the Multiplus started bulk charge.

I need a quicker more reliable method to recover if this occurs. Raising house bank voltage to 11.8 V is key. I thought running the main diesel and charging from the alternator was the answer but, as it's field is held to 0 by the BMS, and any output would be blocked by the Battery Protect relay, this failed. I'm thinking a compact capacitive charger as used for roadside jumps might be an answer, I'm hoping others have suggestions.


Battery Protect
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2 Answers
rush avatar image
rush answered ·

Hi Mate

Had the same issue with the Victron 200amp Smart Battery shuttng down on me. There is a setting in the app to 'power' which wakes these up but I still had an issue with not being able to charge from too low a discharge.

My saviour has been the Victron IP65 Blue Smart charger. This unit woke it up, went through the very low charge cycle until it could then resume Bulk charging. Did it all well.

And yes apparently even in shut down mode from the BMS the battery still discharges [and BMS still takes current? maybe].

My next process will be to completely isolate the battery with master switch when turning off.


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kabyak avatar image kabyak commented ·
Wow, that doesn't leave a warm feeling. I'll visit it tomorrow and see what state I have. I did bring it to 11.8 V at a low current rate then let the bulk charger take over (at a rate of about 20A per battery).
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rush avatar image
rush answered ·

Wouldn't use the jumpstart charger as it doesn't have a BMS and wont use the low amp voltage settings needed and recommended [ ps im not an expert just what I understand and have done ] !.


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kabyak avatar image kabyak commented ·
I checked on my batteries today, I found them fully charged and all batteries balanced. I disconnected shore power and used a heater to place 80A load (16A per battery) via the inverter and monitored discharge for 90 min. At the end I had 12.98V, 57% state of charge (bank is defined as 400Ah), and 122 Ah consumed. This is clearly below rated capacity but not far off what I've observed before this shutdown event. These are only a year old and I don't feel I've ever gotten rated performance from them. Note: I've had several previous shutdowns caused by loss of shore power while the boat was unattended, none as deep as this event.

Very frustrating that this occured with disconnection of all loads except the BMS, it apparently isn't designed to disconnect itself before damage occurs.

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JohnC avatar image JohnC ♦ kabyak commented ·
@kabyak

I can't speak for your BMS, but you seem upset by your battery monitor SOC reading. Presumably that's coming from your BMV. And it's probably not set up correctly, so you're getting excited by erroneous readings.

As an example, your 400Ah batts are rated for that at a 20hour discharge rate, down to an unholy low V. Yet you test at 80A, closer to a 5 hour rate. The result won't be the same, and unless you have the correct parameters programmed into the BMV to compensate for this, then you'll stay disappointed. If you haven't set it up properly (like still on default settings), ignore it.

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kabyak avatar image kabyak JohnC ♦ commented ·
I appreciate your reply but I think you miss my point. I'm unhappy the BMS allowed battery V to drop so low given it's purpose is to protect the batteries. I did set up battery parameters in the BM702 including derating the 5 100Ah battery bank to 400 Ah to help avoid over discharging. My experience with typical use is getting something a bit over 300Ah consumed when V nears the low threshold.

Panbo Blog recently had a piece on setting up battery monitors and I intend to revisit that.

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