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My JK and my meat

BigBrosMo said:
I mean the BMS has the feature on by default, set at 2amps. You said earlier you wouldn't use an active balancer unless absolutely necessary... which suggests I shouldn't use mine. So I am trying to understand why. (other than the phantom load angle - which is a good angle)
Click to expand...
If its configurable enough and part of the bms then its fine.
Its the discrete stupid ones that I object to.
I suggest you make sure that your active balancer only balances above float voltage and only when charging.
I'm also ok with it balancing during charge and discharge but then I would have to get more specific about your charge profile including float voltage.
Which means I would need to know the specifics of your charge profile.
 
Add lead in parallel.

I know this is an unpopular idea, but the lead will keep the SCC alive overnight until solar comes back. Your lead will need to be enough for one night.
 
gelmjw said:
Add lead in parallel.

I know this is an unpopular idea, but the lead will keep the SCC alive overnight until solar comes back. Your lead will need to be enough for one night.
Click to expand...
That's not a bad idea for a temporary solution.
 
I did lead+LFP this past winter in my trailer which was parked/stored in the driveway. During several consecutive cold nights and days, the BMSs Low Temp Disconnect kept the LFP off.

The lead did not shut down, but was ready to automatically reactivate the LFP when warmer weather returned.
 
smoothJoey said:
Could the active balancer be your phantom load?
Click to expand...
I turned the BMS charge and discharge off today manually and could measure 2amps on the cell balancing leads while it was balancing. When I turned balancing off it dropped to 0 amps. The BMS wasn't reporting current out to the shunt but I also couldn't get my meter clamp around the B- lead from the BMS since it's rigid copper bus bar. So I am not sure... do you know if "redistributing" the voltage by balancing is actually consuming power, or does it just "move" the charge around in an efficient way? Also, a friend here on the island randomly has a Battery Protect unit I can have. I'll have to order an SSR but the BP has a "remote relay" output on it I think I can wire right into the "remote" port on my inverter.
 
BigBrosMo said:
I turned the BMS charge and discharge off today manually and could measure 2amps on the cell balancing leads while it was balancing. When I turned balancing off it dropped to 0 amps. The BMS wasn't reporting current out to the shunt but I also couldn't get my meter clamp around the B- lead from the BMS since it's rigid copper bus bar. So I am not sure... do you know if "redistributing" the voltage by balancing is actually consuming power, or does it just "move" the charge around in an efficient way?
Click to expand...
Not sure how efficient it is.
Should be better than a purely resistive balancer but not sure how much is lost in moving from cell to cell via capacitors.
BigBrosMo said:
Also, a friend here on the island randomly has a Battery Protect unit I can have. I'll have to order an SSR but the BP has a "remote relay" output on it I think I can wire right into the "remote" port on my inverter.
Click to expand...
Cool if you can do it without an SSR that is great.
Lets us know what you find.

I want to know if the solar charge controller powers off when only the discharge fets are opened.
Also if it powers back up when they are closed.

Further to that I would like to know if the solar charge controller can recover from the discharge fets opening and closing again if the pv side is not showing any voltage(aka nightime).
 
smoothJoey said:
Not sure how efficient it is.
Should be better than a purely resistive balancer but not sure how much is lost in moving from cell to cell via capacitors.

Cool if you can do it without an SSR that is great.
Lets us know what you find.

I want to know if the solar charge controller powers off when only the discharge fets are opened.
Also if it powers back up when they are closed.

Further to that I would like to know if the solar charge controller can recover from the discharge fets opening and closing again if the pv side is not showing any voltage(aka nightime).
Click to expand...
I actually found in my testing today to your questions that

1) As long as there is sun, when I disable "discharge" and/or "charge" on the BMS, the SCC stays on and keeps powering the inverter! I thought it would shut off in the absence of the battery. As soon as I turn off the PV input, the SCC (and the inverter) stop and then won't restart until I enable charge and discharge again from the BMS. So it's like the SCC needs the battery to start, but can stay on without the battery as long as there is enough solar current (about 5 amps).

2) Yes the SCC can recover from discharge being disabled and then re-enabled at night (I just did it to verify)
 
BigBrosMo said:
I actually found in my testing today to your questions that

1) As long as there is sun, when I disable "discharge" and/or "charge" on the BMS, the SCC stays on and keeps powering the inverter! I thought it would shut off in the absence of the battery. As soon as I turn off the PV input, the SCC (and the inverter) stop and then won't restart until I enable charge and discharge again from the BMS. So it's like the SCC needs the battery to start, but can stay on without the battery as long as there is enough solar current (about 5 amps).

2) Yes the SCC can recover from discharge being disabled and then re-enabled at night (I just did it to verify)
Click to expand...
Good, if I understand correctly you have not found any scenarios where manual intervention is required to resume charging.
Except when bms turns itself "hard off".
Confirm?
 
smoothJoey said:
Good, if I understand correctly you have not found any scenarios where manual intervention is required to resume charging.
Except when bms turns itself "hard off".
Confirm?
Click to expand...
Exactly yes, confirmed. I need to prevent it from getting to the power off stage and will aim to prevent that by putting an LVD in front of the inverter.

Relevant sidebar: Lithium is a new tech for the island. I am one of two people with decent Lifepo4 packs here and the other fellow (the one with the victron Battery protect) and I are at the same level of expertise. That's fine. But the local people... man I really feel for them... they are trying to switch over to lithium as the prices have made it reasonable. Compared to the FLAs used in the past lithium is a no-brainer. They've gotten used to replacing the FLAs every 3 or 4 years and now lithium with it's promise of 3000+ cycles just make economic sense. The issue I see is that all their other equipment is bare bones basic. PWM controllers, minimal panels, cheap chinese inverters (often modified sin wave), lead acid charges etc. Nothing programmable or smart. So along with buying the cheapest Li they can find, they're all going to run into issues with overcharging etc and relying on the BMS to do the work. It's hard to re-teach new tricks to these old dogs when $ is a MAJOR factor. The LVD issue I am going through right now is going to be a common occurrence here and most of them are not going be able to wire something in or afford a Battery Protect let alone understand the problem. It's bittersweet this transition.
 
smoothJoey said:
Not sure how efficient it is.
Should be better than a purely resistive balancer but not sure how much is lost in moving from cell to cell via capacitors.

Cool if you can do it without an SSR that is great.
Lets us know what you find.

I want to know if the solar charge controller powers off when only the discharge fets are opened.
Also if it powers back up when they are closed.

Further to that I would like to know if the solar charge controller can recover from the discharge fets opening and closing again if the pv side is not showing any voltage(aka nightime).
Click to expand...
Arg. Can someone explain to me HOW to connect the Battery Protect to the remote port on the Inverter? I don't understand how to wire it....

1. Pos+ comes from positive system bus to BP + IN.
2. BP + OUT goes to where?
3. Remote switch on inverter has a + and - lead. Where do they go on the BP? ie. if I put my meter across the yellow + wire and the red - wire of the remote cable, I see the battery's voltage. What ports on the BP do they connect to?

I've looked at the diagrams (all they do is show victron inverters with some Ve.Bus) and posts and everything just says "you can use the BP to wire direct to your inverters remote port" Great. HOW?!?!
 
BigBrosMo said:
Exactly yes, confirmed. I need to prevent it from getting to the power off stage and will aim to prevent that by putting an LVD in front of the inverter.
Click to expand...

Why not just put the BMS under voltage at 3.1V or something in that range instead of 2.8V and the reconnect at 3.25V or so? That 3.1V limit should be enough to keep your BMS going for quite some time before it gets to the shutdown voltage, and your SCC will see the battery and charge it just fine. With a higher reconnect voltage you can handle the initial fridge surge etc. without the BMS turning off again.
 
upnorthandpersonal said:
Why not just put the BMS under voltage at 3.1V or something in that range instead of 2.8V and the reconnect at 3.25V or so? That 3.1V limit should be enough to keep your BMS going for quite some time before it gets to the shutdown voltage, and your SCC will see the battery and charge it just fine. With a higher reconnect voltage you can handle the initial fridge surge etc. without the BMS turning off again.
Click to expand...
As soon as it hits undervoltage the SCC turns off though. So it will never get to a reconnect voltage.
 
Why would the SCC turn off in case of low battery voltage?

SCC turning off at some point should be considered as a fault. The SCC should be able to keep running when the inverter is off and whenever the panels are producing power it should start charging. If this is due to the SCC configuration it should be fixed.
 
BigBrosMo said:
As soon as it hits undervoltage the SCC turns off though. So it will never get to a reconnect voltage.
Click to expand...

The discharge path will be disconnected, not the charge path and the SCC will work fine since it sees the battery. Only when the BMS reaches shut-down voltage does the BMS turn off fully.

diysolarforum.com

BMS MOSFETs Explained

I'm writing this post since it seems there is a lot of confusion (especially in the comment section of a certain youtuber in Australia) on why both MOSFETs in a typical single port BMS are controlled individually and why/how this works when they're in the same series circuit. It will hopefully...
diysolarforum.com diysolarforum.com
 
upnorthandpersonal said:
The discharge path will be disconnected, not the charge path and the SCC will work fine since it sees the battery. Only when the BMS reaches shut-down voltage does the BMS turn off fully.

diysolarforum.com

BMS MOSFETs Explained

I'm writing this post since it seems there is a lot of confusion (especially in the comment section of a certain youtuber in Australia) on why both MOSFETs in a typical single port BMS are controlled individually and why/how this works when they're in the same series circuit. It will hopefully...
diysolarforum.com diysolarforum.com
Click to expand...
I think that's assuming separate port charge/discharge. If it's a common port BMS how do you expect that to work? Like has already been stated, BMS is last line of protection. Shouldnt be relying on it to shut the inverter off. He needs to conjure up the LV disconnect for the inverter at a high enough voltage that would allow the SCC to remain on (perhaps overnight) until the sun can start charging again. If a cloudy couple days, then batteries will hit BMS LVD and shut down, requiring manual intervention.

He has the victron battery protect. All he has to do is figure out how to make it control his inverter and set its shutdown voltage.
 
Last edited:
DerpsyDoodler said:
If it's a common port BMS how do you expect that to work?
Click to expand...

Exactly like I wrote in that post I linked to. I have the same BMS. It can control charge and discharge independently, even if it's a common port BMS - it uses the body diode of the MOSFET for this. Low voltage disconnect disables discharge, but allows charge. High voltage disconnect disables charge, but allows discharge.
 
but if discharge is disabled, then SCC gets no power. That situation would only be useful if you had a charging system powered completely independent of the LFP bank it is charging. Also, i made edits to my previous post, please refer back.

edit: (or a charging system that bypasses the BMS which I am NOT recommending, just stating for the sake of accuracy).
 
Last edited:
upnorthandpersonal said:
Exactly like I wrote in that post I linked to. I have the same BMS. It can control charge and discharge independently, even if it's a common port BMS - it uses the body diode of the MOSFET for this. Low voltage disconnect disables discharge, but allows charge. High voltage disconnect disables charge, but allows discharge.
Click to expand...
When UnderVoltageProtect is active, discharge stops, so the SCC has no power. It shuts off. The only time it stays on is if the panels are receiving power, then it powers itself. As soon as I disable the panels, SCC turns OFF. Every time.
 
upnorthandpersonal said:
The SCC should see the voltage of the battery and power on when solar is available. If not, it's a very crappy SCC. Andy from off grid garage had a similar situation a while ago:

Click to expand...
OK. There's a disconnect here. Let's step through this.

BMS is common port but can still allow charge and discharge independently. When discharge is disabled, how do you expect the SCC to "see" the battery? SCC and inverter are connected to the same bus. if the SCC can see the battery, then so can the inverter.
 
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