diy solar

diy solar

Battery Disconnect Switch OR Resistor?

T

TedH

New Member
Joined
Jun 5, 2020
Messages
186
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."
 
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.
 
justinm001 said:
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.
Click to expand...
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.
 
Last edited:
TedH said:
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.
Click to expand...
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.
 
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."
Click to expand...
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.
 
Skypower said:
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.
Click to expand...
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
 
$280 solves all these issues. I got tired of BMS's shutting down so installed this beast. It has been 100% reliable.

battlebornbatteries.com

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 battlebornbatteries.com

1-9.png
 
justinm001 said:
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
Click to expand...
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. IMG_1370.jpeg
 
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
Click to expand...
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.
 
corn18 said:
$280 solves all these issues. I got tired of BMS's shutting down so installed this beast. It has been 100% reliable.

battlebornbatteries.com

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 battlebornbatteries.com

1-9.png
Click to expand...
Is this always connected? If so, are similar 'DC surge limiters/battery protectors' from Victron and others sufficient for less than $280-300?
 
corn18 said:
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.
Click to expand...
Haven’t found anything wife proof or ease the pain of a verbal dig. Yup got the button on the box too.IMG_1371.jpeg
 
TedH said:
Is this always connected? If so, are similar 'DC surge limiters/battery protectors' from Victron and others sufficient for less than $280-300?
Click to expand...
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.
 
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
Click to expand...
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
 
TedH said:
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
Click to expand...
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.
 
TedH said:
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
Click to expand...
Correct on all accounts. Even though the switch isn’t rated for DC, the resistor limits the arc within.
 
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.
 
Do make sure the switches you get are momentary, normally open. It isn’t perfect, it’s Amazon 😂
 
Skypower said:
Correct on all accounts. Even though the switch isn’t rated for DC, the resistor limits the arc within.
Click to expand...
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.
 
You must log in or register to reply here.

Similar threads

M
Think I understand
Replies
5
Views
246
Meeko
M
T
Portable Power Station w Alternator Charging
Replies
19
Views
775
RV8R
R
D
DC fuse block vs CB/switchblock, for 400W small Truck popup system?
Replies
4
Views
339
justinm001
J
J
Inverter Bypass Switch
Replies
9
Views
290
Ampster
Ampster
K
Starter battery kill switch
Replies
5
Views
352
mikefitz
mikefitz
Back
Top