Solar system mode while in storage

[Yellowbird911]

Have most of my solar system and will start install soon but one question I have that I can't seem to find is what to do while the bus in storage? It may sit for two to three months in the winter between usage. Not sure I want everything powered up while it sits unattended. Using 280ah LiFe 24 volt batteries with 200 amp Daly BMS, 3000k all in one inverter/ charger and 1300 watts of solar.

Thought about just using a disconnect switch which will be there for service and safety but from what I have seen flipping the switch is hard on the inverter capacitors and a resistor should used to charge them up before connected battery voltage.

Thanks

[john61ct]

Isolate the LFP cells completely at low voltage * while in storage, from all loads and charge sources, and most especially from the BMS.

Never keep them at high SoC% except when actively being cycled anyway

but if for longer than say a day or two, get them down to below 50%

no need to be precise, but not "too low" *

Yes this is the opposite of proper care for a lead bank.

If for longer than a couple weeks, check the bank voltage regularly until you can predict the self-discharge rate, if any

top up with a little charge input enough to prevent the pack ever dropping below 3Vpc (* that is conservative to be safe)

a bit more energy will make the required interval longer, but not up over 3.2Vpc at rest.

. . .

As for loads that **need* running unattended, substitute a cheap lead batt

which could be left on Float charge level if your solar can be adjusted , i.e. set the CV / Absorb setpoint to the same as Float V

[Danjo]

Hey John, what about when running AGMs? Is my charge controller taking care of business or am I ruining my batteries?

OP, thanks for bringing this up

[Yellowbird911]

Have a lot of experience with LiFe and LiPo from another hobby but not in a solar application so I have some more questions.

1. Does the Daly BMS draw power when there is no load from the inverter?

2. If so does disconnecting the main power lead to the Daly stop the draw or do you have to disconnect the cell leads also?

3. Do you pre-charge the capacitors in the inverter every time or can they take the hit from just flipping the main switch and connecting the batteries?

Thanks

[john61ct]

Originally Posted by Danjo

Hey John, what about when running AGMs? Is my charge controller taking care of business or am I ruining my batteries?

Definitely never trust any charge source, even those costing thousands need adjustment from default settings for the specific battery type and use case, as conditions change

All lead chemistries need to be kept at 100% SoC for as much as possible of their lifespan to get good longevity.

But if you spend big money on proper deep cycling AGM and GEL

they are shorter lived and a lot fussier to care for than FLA

you need to make sure they don't get too over charged, and lose electrolytes out their valves as gas, that cannot be replaced.

Every good battery maker has detailed spec sheets showing the correct profile

not just Absorb/CV voltage setpoint range

but Float V

and endAmps termination current

Few charge sources get this right without careful calibration using an accurate DMM and ammeter at the bank posts.

Never trust the charge sources' readouts.

Now, if you're just buying cheap crap batts from big box retail or automotive channels

and are OK with replacing them every 2-4 years

then likely you won't want to bother going to too much trouble.

But a big bank costing thousands, able to reliably last 6-8 years

or 12+ with FLA

then IMO learning how to truly coddle them.

Not discharging below 50% except for emergencies is part of it too.

[Rucker]

Originally Posted by Yellowbird911

Have a lot of experience with LiFe and LiPo from another hobby but not in a solar application so I have some more questions.

1. Does the Daly BMS draw power when there is no load from the inverter?

2. If so does disconnecting the main power lead to the Daly stop the draw or do you have to disconnect the cell leads also?

3. Do you pre-charge the capacitors in the inverter every time or can they take the hit from just flipping the main switch and connecting the batteries?

Thanks

1. My Daly shuts off after a predetermined time period (programmable) and automatically fires up whenever there is a load. When off, I don't know what the draw is but I'm sure it exists. Same with a shunt. I'll check next time I'm looking at the battery.

2. You would need to disconnect all leads. Each cell is monitored separately, so each lead other than the first negative and last positive lead operates both as a positive lead (for the current cell) and negative lead (for the adjacent cell).

If you have over 200 amp hours in the battery that's a looong time for millivolts to grind the battery down. It's worth researching to see if raising the lower bound for the BMS (e.g. above 2.4V per cell) before storing the rig might do a good job shutting things down.

3. If my Renogy inverter is typical of inverters there will be inrush present at first connect, after some period of inactivity. I don't know how big the inrush is, but remember that inrush is the same thing as dead short. I would recommend wiring in a resistor and momentary switch, or at least having one handy to bridge across the circuit breaker before flipping it. A quick online search doesn't help clarify the size of the spike but does offer some insight into the bad things that happen with inrush from downstream loads.

I'm guessing those capacitors are what give the inverter its peak wattage rating, so just like you don't want to run your inverter at its peak wattage, there is a cost in the form of wear and tear. Maybe the damage is cumulative, maybe it's negligible for our systems.

I bought a pair of 50W 25 Ohm resistors and momentarily bridge the gap between the shunt and the BMS to precharge before connecting the cable.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1