9v across Lithium battery when switched off.

[dally]

Hi, I'm new to Lithium. I have just fitted one. a new Fogstar Drift 230amp. Other than fit it, I have done nothing to it, i.e. charge it or discharge it and the app says, 50% full, 1 cycle.

With the previous Lead Acid battery fitted, after about 5 days in storage, I found it had discharged down to 4v, so probably it's finished but no problem, I was there to replace it with the Lithium.
I should add, the vehicle is new to us and is a caravan to replace our motorhome.

Bearing in mind the possible currant drain and not knowing when I can get back up to the van which is in storage. I decided to turn the battery off on the app. Just for fun I decided to check voltage across the terminals after I had turned it off. I was surprised to see it read between 8 and 9 volts. I rang Fogstar, who after talking to someone else, said, that's normal but it takes 4 or 5 cycles for the BMS to get up to speed as it were. I couldn't see the connection between the cycles and the voltage when supposedly turned off, I wasn't convinced. I'd have thought off was off.
I know there are many on here with vast experience with Lithium, what's your thoughts please?

 

[Spriddler]

With the previous Lead Acid battery fitted, after about 5 days in storage, I found it had discharged down to 4v,

IKBA about lithium but from that info it would seem that the cause of low voltage (e.g. parasitic drain) may have existed before you fitted the lithium battery.

 

[StillGoing]

You can’t trust what the app says, especially if you haven’t fully charged the battery. The app is notoriously inaccurate especially if the battery has low current discharge.

If you want to know how full the battery is, you first need to fully charge it (with a LifePo4 charger) and ideally install a shunt.

 

[Raul]

Hi, I'm new to Lithium. I have just fitted one. a new Fogstar Drift 230amp. Other than fit it, I have done nothing to it, i.e. charge it or discharge it and the app says, 50% full, 1 cycle.

With the previous Lead Acid battery fitted, after about 5 days in storage, I found it had discharged down to 4v, so probably it's finished but no problem, I was there to replace it with the Lithium.
I should add, the vehicle is new to us and is a caravan to replace our motorhome.

Bearing in mind the possible currant drain and not knowing when I can get back up to the van which is in storage. I decided to turn the battery off on the app. Just for fun I decided to check voltage across the terminals after I had turned it off. I was surprised to see it read between 8 and 9 volts. I rang Fogstar, who after talking to someone else, said, that's normal but it takes 4 or 5 cycles for the BMS to get up to speed as it were. I couldn't see the connection between the cycles and the voltage when supposedly turned off, I wasn't convinced. I'd have thought off was off.
I know there are many on here with vast experience with Lithium, what's your thoughts please?

Only way sure about it, is to fully charge, then try to switch off discharge, (leave charge on) while have a light or small bulb fitted to it. If the light goes off all good, despite reading some voltage. Voltage may be present but without current flow, a solar charger needs to see voltage to stay on.

 

[growly_bear]

I finished building my own LiFePo4 battery using 4 x 280 Eve cells from Fogstar, but bought my JBD BMS directly from Jaibaida as the Fogstar one didn't have the heater terminal. When I connected everything, like you, I measured the voltage across the battery and found it to be 9.2V when the discharge and charge (using the software switch) was turned off. I measured the resistance (can't remember the value), but the current calc worked out to be small, like 10mA.

I got in touch with Jaibaida, who said this is normal as the BMS uses energy to keep itself powered even when turned off. A recent youtube video by Will Prowse stated that a battery will self discharge by anything between 1 and 3% per day. Check at 1:40

I'm still learning, but the cycles thing in this case in my opinion is nonsense and not relevant to your question.

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[Raul]

Per month 1% if stored on cold and 3% if stored at 20 and above.

 

[Lenny HB]

Don't bother with the app it you want to effectively turn the battery off fit a battery cut off switch or remove the fuse.
If you want to know the true state of your batteries fit a shunt.

 

[Raul]

I finished building my own LiFePo4 battery using 4 x 280 Eve cells from Fogstar, but bought my JBD BMS directly from Jaibaida as the Fogstar one didn't have the heater terminal. When I connected everything, like you, I measured the voltage across the battery and found it to be 9.2V when the discharge and charge (using the software switch) was turned off. I measured the resistance (can't remember the value), but the current calc worked out to be small, like 10mA.

I got in touch with Jaibaida, who said this is normal as the BMS uses energy to keep itself powered even when turned off. A recent youtube video by Will Prowse stated that a battery will self discharge by anything between 1 and 3% per day. Check at 1:40

I'm still learning, but the cycles thing in this case in my opinion is nonsense and not relevant to your question.

I don't now about the JBD but, JK bms, apparat of the control app channels charge discharge, you have a port for a low power hard wired switch that switches the battery completely off.

 

[Pausim]

If you turned it off with the App then at the very least it must still be powering the Bluetooth connection.

 

[growly_bear]

If you turned it off with the App then at the very least it must still be powering the Bluetooth connection.

On one of the tests I did when I was measuring mine, I disconnected the bluetooth ribbon cable, and measured. Still drawing a very small current. I'm not disagreeing with you, just mentioning that the BMS still draws a current even when the main +ve and -ve are not connected in circuit. The MOSFET's must have a 0V reference to open or close...??

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[growly_bear]

I don't now about the JBD but, JK bms, apparat of the control app channels charge discharge, you have a port for a low power hard wired switch that switches the battery completely off.

mmm My JBD BMS https://jiabaida-bms.com/products/j...-with-uart-heating-function-series-connection

does have an on/off switch port, and I bought a JK BMS on/off switch from OffGrid. The switch isn't a latching sort, it's just momentary, so I didn't bother to fit it as I thought it would have the same effect as the software switch.

 

[LithiumConvert]

I have just fitted a new LiFePO4 battery. Other than fit it, I have done nothing to it, i.e. charge it or discharge it.

Are they not delivered uncharged? Mine were.

They need to fully charged before use, or testing.

 

[Lenny HB]

Are they not delivered uncharged? Mine were.

They need to fully charged before use, or testing.

Fogstars come approx 30% charged & it's recommended you give them 4 or 5 full cycles before fitting.

 

[LithiumConvert]

It's recommended you give them 4 or 5 full cycles before fitting.

Many of us don't have any way to cycle them without using the motorhome charger, etc.

But your point is still valid, if you say before general use.

 

[autorouter]

How did you check the voltage across the battery? Was it with a multimeter? A multimeter has a very high resistance, so it would draw a very small current, only a few microamps if that. You could try connecting a small load across the terminals, and you may find that the voltage drops to practically zero. That 9V or so could just be the open circuit voltage of the BMS.

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[growly_bear]

Many of us don't have any way to cycle them without using the motorhome charger, etc.

But your point is still valid, if you say before general use.

I was thinking about how to put a few cycles on mine as I haven't the ability to isolate the output from the DCDC without removing the fuse. Thinking of running a 1kw heater for 3 hours!!

 

[growly_bear]

How did you check the voltage across the battery? Was it with a multimeter? A multimeter has a very high resistance, so it would draw a very small current, only a few microamps if that. You could try connecting a small load across the terminals, and you may find that the voltage drops to practically zero. That 9V or so could just be the open circuit voltage of the BMS.

This is exactly what happened to me. With the BMS off, I connected a small computer fan, and the voltage dropped to 0.9V

As ever autorouter, thanks for explaining why!

 

[Pausim]

Are they not delivered uncharged? Mine were.

They need to fully charged before use, or testing.

My Roamer arrived 45% charged and they do a full bench discharge/charge cycle before dispatch so they can issue a certificate confirming the performance. They say it will take a further 1 or 2 cycles before the state of charge figure is accurate but that this doesn’t affect performance so it can be installed straight away.

When my Relion battery was delivered nearly 7 years ago it arrived 50% charged. Both my home use power banks arrived at 40% to 50% too.

I have never heard of LiFePO4 being shipped or stored fully discharged before but that doesn't mean it can’t happen.

 

[dally]

Thanks everyone for your replies. I am suitably reassured about the 9v and I appreciate the explanation. I'm going to struggle to get 4 or 5 cycles into it before fitting but I'm sure I'm not the only one.

As for the parasitic drain, well, it may well be that I have left something on by accident. I'll know more when I get a feel for the electrical system.