Battery Disconnect Switch OR Resistor?

justinm001 · Apr 19, 2024

I wouldn't want to deal with having to hold a button to get things started. I have 2x 48v 100a SOK batteries and 2x 5kw quattro inverters. 50% of the time they start just fine without any precharging or anything, and this is at night without solar. They have built in precharge but I never remember how. I'm not sure if the inverters capacitators stagger start or what, as to restart the inverters I need to turn off then on and they have separate switches so take a second, also they sync up.

If that doesn't work I just turn the key to on and then it'll use the chassis dc converter to precharge, then i'll reset the bms on the batteries.

I think I broke my EG4 12V battery BMS's as I don't think they do anything anymore. I've seen the alm light come on sometimes but they still work.

Dave in AZ · Apr 19, 2024

corn18 said:
The input capacitors on inverters can draw a lot of current really fast when they are charging. LiFePO4 batteries can provide a lot of current really fast. The BMS might see this as a fault and put the BMS into protect. Now you have to find a way to wake up the BMS which is not as simple as it sounds.

My SOK batteries had no issues with a 1200W or 2000W Xantrex inverter. They really did not like my Victron MPII 3000. They went into protect every time. The precharge circuit charges the inverter caps before you connect the batteries. A simple, elegant and cheap solution.

If you forget to precharge, you will have the pleasure of tracking down a 15V DC power source to wake them up. My solar wouldn't wake them up. My truck charge line wouldn't wake them up. A smart 120V battery charger wouldn't wake them up. I made a small battery pack with a buck converter to wake them up. What a giant PITA.

Thanks much.

HarryN · Apr 19, 2024

corn18 said:
What about night time?

If the power system in general is kept in an always on state, then the inverter input caps will also stay pre-charged.

Then you can just use the switch on the inverter or the remote to turn it on. The main reason to turn an inverter off is the 20 - 30 watt standby power when it is on.

Once you have 300 + watts of solar on a vehicle that is parked outside, the only reason that I would turn off the power system is to work on it. My explorer just has 150 watts because that is all that will fit on the roof and I just turn the inverter off when not in use, but I only use that thing for running power tools.

There isn't any reason to turn off the breaker between the battery pack and the inverter normally.

If you have enough solar to keep the battery 90% SOC even with the inverter on - just leave it on all of the time.

corn18 · Apr 21, 2024

Just had a situation where a precharge would not have worked. I've had this happen before. I was load testing my new install. Had one a/c fan on (500W) then turned the fireplace on low (900W), then high (1500W). The inverter shut down. It went through it's reset cycle then came back on. All was good with my surge limiter. But if that happened with just a precharge, my BMS(s) would have gone into protect and I would be cursing.

The inverter reset because I only had one battery hooked up and 2000W overloaded the one BMS. Oops. I flipped the main 50A CB off before the inverter reset to prevent another overload.

TedH · Apr 22, 2024

Skypower said:
The FETS are there to shut down as a last resort and the inrush is massive and so fast that it’s usually waaay more than they are rated for. Hold down a momentary switch for 5 seconds to a 25 watt 30 ohm resistor right before you close the switch is cheap insurance. There’s just no need to beat up your system. When a charger powers up from the AC side, you may hear a groan from an inrush but the power line and transformer greatly ease this in comparison to the potential of a battery. View attachment 210294

Just want to confirm where the pre-charger fits in the schematic diagram. From this image, the wires are coated red. I note on the Battleborn capacitor limiter, it says to connect between Bat negative and Inverter negative to precharge. Is this correct?

TedH · Apr 25, 2024

TedH said:
In my current RV solar power wall, I use a 600amp blue sea rotary switch as a quick connect between the Lifepo4 battery and the rest of the 24vdc system (inverter charger, solar charge controller and secondary 24vdc charger). I turn the blue sea switch "ON" before I switch the Aims inverter "ON" and switch the PV breakers on that feed solar to the solar charge controller. When I upgraded from 24vdc/200ah to 24vdc/600ah, my 300amp blue sea switch would overheat and fail. The 600amp switch appears to handle the 'rush'. It still makes a hot sound when the amps rush through it initially. I then turn on the Aims inverter.

Q: Before I switch to my Victron Multiplus II 24v 2x120 inverter/charger, do I need to add a resistor to bypass the power switch and pre-charge my Victron inverter capacitors? Does my blue sea switch act as a sufficient resistor between the battery and inverter, rest of the 24vdc systems?

NOTE: I 'assumed' the switch provides the resistance/protection given it has 'ignition protection' built in. My Aims inverter/charger has lived happily in this configuration since 2021.

From the AI on Google search: "The Blue Sea Systems E-Series Master Battery Switch Single Circuit is typically used between a battery bank and an inverter. It is slightly larger and has a higher current rating than the High Current On/Off Mini Switch (6006). It is recommended to use this switch with 3000VA inverters."

I received my resistor and pack of LEDs. I have installed on a 1-OFF-2 switch. The resistor is much further away from the OUT pole than pictured.

Battery Disconnect Switch OR Resistor?

justinm001

Solar Addict

Dave in AZ

Solar Enthusiast

HarryN

Solar Enthusiast

corn18

Village Idiot

TedH

New Member

TedH

New Member

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