Battery Disconnect Switch OR Resistor?

[TedH]

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."

 

[justinm001]

The amount of batteries have no effect on the size of wiring or the on/off switch. Amp hour is different than amp.

Now you have more batteries the recharge load is more spread out and might be fine without a resistor. Not sure if the bluesea has anything to do with the precharge.

I've always turned on my solar and let it do the precharge then turn on the batteries.

 

[TedH]

The amount of batteries have no effect on the size of wiring or the on/off switch. Amp hour is different than amp.

Now you have more batteries the recharge load is more spread out and might be fine without a resistor. Not sure if the bluesea has anything to do with the precharge.

I've always turned on my solar and let it do the precharge then turn on the batteries.

My Aims solar charge controller installation manual requires battery connection before PV breakers turn on "to protect the solar charger from damage". It appears to require the battery power to operate properly. It shuts down when/if my battery goes offline (I assume to protect the solar charge controller). BMS shuts battery down if protection parameters are exceeded.

 

[justinm001]

My Aims solar charge controller installation manual requires battery connection before PV breakers turn on. It appears to require the battery power to operate properly. It shuts down when/if my battery goes offline (I assume to protect the solar charge controller) due to protection imposed by the BMS.

How does it know? If you turn on your batteries and it's sunny out then you turn off the batteries I'd assume the mppt wouldn't know the batteries are off as it's outputting the voltage.

I've ran my batteries empty and the solar has turned my system back on but now I'm not sure if the batteries went to 0 or just below 5% where the inverter shuts off.

 

[Skypower]

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."

It’s not just about the switch being able to handle the inrush, it’s about not blowing up the capacitors inside chargers, inverters or the FETS in a bms. Always precharge before closing a DC battery circuit or follow the directions for batteries equipped with pre charge. Unless it’s an emergency, reduce load or turn off the equipment before opening the disconnect.

 

[justinm001]

It’s not just about the switch being able to handle the inrush, it’s about not blowing up the capacitors inside chargers, inverters or the FETS in a bms. Always precharge before closing a DC battery circuit or follow the directions for batteries equipped with pre charge. Unless it’s an emergency, reduce load or turn off the equipment before opening the disconnect.

How does that work specifically? Inverters are charging capacitors so one shouldn't be able to negatively affect one in another device, right? The FETS and such are specifically designed to protect the batteries so should be able handle any inrush

 

[corn18]

$280 solves all these issues. I got tired of BMS's shutting down so installed this beast. It has been 100% reliable.

Current Surge Limiter

Do you have Battle Born Batteries in your rig? Does your system have a 4kw or greater inverter? Then protect your system with our Current Surge Limiter!

battlebornbatteries.com

 

[Skypower]

How does that work specifically? Inverters are charging capacitors so one shouldn't be able to negatively affect one in another device, right? The FETS and such are specifically designed to protect the batteries so should be able handle any inrush

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.

 

[corn18]

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

The precharge works excellent and is a LOT cheaper than that current limiter. I had one in my camper but it was not wife proof so I had to replace it with the $280 wife proof version. Mine was in a little project box with a pretty red button that said "Push First". But she didn't. ANd both batteries shut down and I was off doing something else and she had no power and she asked me why we spent $56k on a trailer that didn't work.

 

[TedH]

$280 solves all these issues. I got tired of BMS's shutting down so installed this beast. It has been 100% reliable.

Current Surge Limiter

Do you have Battle Born Batteries in your rig? Does your system have a 4kw or greater inverter? Then protect your system with our Current Surge Limiter!

battlebornbatteries.com

Is this always connected? If so, are similar 'DC surge limiters/battery protectors' from Victron and others sufficient for less than $280-300?

 

[Skypower]

The precharge works excellent and is a LOT cheaper than that current limiter. I had one in my camper but it was not wife proof so I had to replace it with the $280 wife proof version. Mine was in a little project box with a pretty red button that said "Push First". But she didn't. ANd both batteries shut down and I was off doing something else and she had no power and she asked me why we spent $56k on a trailer that didn't work.

Haven’t found anything wife proof or ease the pain of a verbal dig. Yup got the button on the box too.

 

[corn18]

Is this always connected? If so, are similar 'DC surge limiters/battery protectors' from Victron and others sufficient for less than $280-300?

This is always connected. It has a lot of electronic bits sandwiched between the giant aluminum thingies.

Don't know about other options. I found this one, bought it, it works so I stopped looking.

 

[TedH]

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

This appears wired to bypass the Battery on/off switch and to be activated only when the button is pushed to precharge. I assume I can set up with permanent connections by connecting to the in and out studs on my battery switch and put in a small plastic box/container on my power wall next to my battery on/off switch.

I see a similar resistor listed on Amazon: https://www.amazon.com/uxcell-Aluminum-Resistor-Wirewound-Resistors/dp/B07D1ZTKDS

Will this on/off button switch work: https://www.amazon.com/DIYhz-Momentary-Pushbutton-Switches-Normally/dp/B08B1PWJ21/ref=sr_1_15?crid=DO7O5I269Q4V&dib=eyJ2IjoiMSJ9.DuY35t9xrPEV4SUfXOIzPsWbXFsMQ7EguDu-VeN3RKTpX9oJS-knnp8kFOm1Nkl8Ex-1qdOwocTj2CVQbkWDASSw1rs0w94uxtbW4Rh1A2ZMGFNYjox3TGASpWt6jlfhvPpSMKJQVyvZ-pF3PskRvcO3MmWu9ArMyM6P4LqXCD-XCoMYzClVFrn7a13GQ1c1ub9vAy9qaeuXlj0TuoCYiZVPCKmx6c_PLCOezRoVdcVdfC2SqdzxFu8hHEePMOJJLfPupU6ej8xpgRO8a97uLH03sc8JQ0ctWhYp-yi5yoU.p2fI8DoVI_8BR0O75emHN3yIGlgZoakahxFNqAaBx4I&dib_tag=se&keywords=25+watt+button+switch&qid=1713548004&s=industrial&sprefix=25watt+button+switch,industrial,122&sr=1-15

 

[corn18]

Is this wired to bypass the Battery on/off switch and to be activated only when the button is pushed to precharge? I assume I can set up with permanent connections by connecting to the in and out studs on my battery switch and put in a small plastic box/container on my power wall next to my battery on/off switch.

I see a similar resistor listed on Amazon: https://www.amazon.com/uxcell-Aluminum-Resistor-Wirewound-Resistors/dp/B07D1ZTKDS

Will this on/off button switch work: https://www.amazon.com/DIYhz-Moment...x=25watt+button+switch,industrial,122&sr=1-15

That's what I used. I had it wired to my battery on/off switch. It's not a blue smoke hazard because the amps are so low. Just don't hold the switch in for a long time. One second does the trick.

 

[Skypower]

Is this wired to bypass the Battery on/off switch and to be activated only when the button is pushed to precharge? I assume I can set up with permanent connections by connecting to the in and out studs on my battery switch and put in a small plastic box/container on my power wall next to my battery on/off switch.

I see a similar resistor listed on Amazon: https://www.amazon.com/uxcell-Aluminum-Resistor-Wirewound-Resistors/dp/B07D1ZTKDS

Will this on/off button switch work: https://www.amazon.com/DIYhz-Moment...x=25watt+button+switch,industrial,122&sr=1-15

Correct on all accounts. Even though the switch isn’t rated for DC, the resistor limits the arc within.

 

[TedH]

Thanks Skypower for a smart solution that fits my pocket weight $$$

 

[Skypower]

Just for giggles;
After installing the discharge circuit, put a volt meter across the terminals of the open disconnect switch and note the voltage. Now push the momentary switch and see how fast voltage drops. Release and notice how slowly the voltage climbs back up. This gives you an idea of how much time you have to work with.

 

[Skypower]

Do make sure the switches you get are momentary, normally open. It isn’t perfect, it’s Amazon

 

[Dave in AZ]

Correct on all accounts. Even though the switch isn’t rated for DC, the resistor limits the arc within.

I don't understand this precharge. Can you explain why, and what is going on? Is this needed for all inverters, or just a certain size? Thanks.

 

[TedH]

Haven’t found anything wife proof or ease the pain of a verbal dig. Yup got the button on the box too.View attachment 210296

I like this. Contained.

 

[corn18]

I don't understand this precharge. Can you explain why, and what is going on? Is this needed for all inverters, or just a certain size? Thanks.

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.

 

[Pappion]

A-B-off battery switch could be wired up with the resistor. Off to A (resistor) to B (on)

 

[corn18]

A-B-off battery switch could be wired up with the resistor.

That is a great option, too. I had it that way and my wife went to B instead of A first. Arrrrrgggghhhhh!!!! I guess I needed an interference method so it had to go through A before A+B. I could see her just switching it to A and leaving it there and then telling me the power didn't work again.

 

[corn18]

A downside to the precharge circuit is if the inverter decides it needs to reset for some reason. When it powers back on, it may send the BMS(s) into protect. That happened to my wife as well.

 

[TedH]

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.

Is the 15V DC power source required for a 12v Multiplus II and not the 24V Multi?