Is my system safe?

I built this little 12v system to have some usable power during an outage and maybe run my tv/router/etc for free year round. I have not slid it into its permanent home and hooked up the single 250w rich solar panel I have yet, but I have used the 20a plug in charger I got incase my bank is low and I know a storm is rolling in. First question starts there, what voltage should it be charging to? I unplugged it when the shunt said 13.5v. On the other side of that, when should the Bms trip the low voltage disconnect? They are li time 100ah batteries and I stopped the test at 10.8v. Li time shunt and charger, voltage verified with multimeter.

Just recently got this set up complete and during that testing I noticed a few things getting warm. The 300a anl fuse gets the hottest (170f+) and the temp spreads from there. The 250a breaker gets warmer than the inverter cables. Buss bar is from a car audio place, nickel coated copper and rated for 600a, switch is a 350a blue seas, plan to add a back up bank down the road. Everything between the battery bank and bus bars is 2/0 and only the wire close to the fuse gets warm. It is 1/0 between each battery and from the bus bars to inverter, all ofc, no cca wire in my system.

The small blue seas fuse thing runs a little 2-3a battery charger and usb distribution block, will add a couple 12v LED’s eventually.

Should I up any wire sizes or swap for a different kind of fuse? Any other suggestions/feedback on my set up? Plan to add more panels and run a cable out that I can hook up to my truck if you’re wondering why I have that charge controller.

What size inverter?

Austin92 said:

Just recently got this set up complete and during that testing I noticed a few things getting warm. The 300a anl fuse gets the hottest (170f+) and the temp spreads from there.

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Concerned about that temp. What current were your drawing? Suspect poor connection around the fuse, rather than the fuse itself, IMHO, but I'm no expert on 12V systems.

Only other comment would be to put insulated cover over the +ve bus bar and fuse, once the temp issues are resolved. Looks too easy to short between +ve and -ve with a wrench or similar on that end panel, which wouldn't be good if it was shorted the wrong side of the ANL fuse.

Austin92 said:

I built this little 12v system to have some usable power during an outage and maybe run my tv/router/etc for free year round. I have not slid it into its permanent home and hooked up the single 250w rich solar panel I have yet, but I have used the 20a plug in charger I got incase my bank is low and I know a storm is rolling in. First question starts there, what voltage should it be charging to? I unplugged it when the shunt said 13.5v. On the other side of that, when should the Bms trip the low voltage disconnect? They are li time 100ah batteries and I stopped the test at 10.8v. Li time shunt and charger, voltage verified with multimeter.

Just recently got this set up complete and during that testing I noticed a few things getting warm. The 300a anl fuse gets the hottest (170f+) and the temp spreads from there. The 250a breaker gets warmer than the inverter cables. Buss bar is from a car audio place, nickel coated copper and rated for 600a, switch is a 350a blue seas, plan to add a back up bank down the road. Everything between the battery bank and bus bars is 2/0 and only the wire close to the fuse gets warm. It is 1/0 between each battery and from the bus bars to inverter, all ofc, no cca wire in my system.

The small blue seas fuse thing runs a little 2-3a battery charger and usb distribution block, will add a couple 12v LED’s eventually.

Should I up any wire sizes or swap for a different kind of fuse? Any other suggestions/feedback on my set up? Plan to add more panels and run a cable out that I can hook up to my truck if you’re wondering why I have that charge controller.

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13.5 is a good charging voltage for 12v
Look into your battery spec for low cutoff. I would imagine in the 10.5v range
Fuses get warm, but not usually that warm. Check connection tightness.

What kind of amperage are you running through this whole system? That will tell you what size wire you need. If you're peaking at 300A and holding there, 2/0 might be a smidge too small.

This mostly looks good. A few callouts.

This tiny wire should be fused as a just in case. (I say tiny, white's probably 6ga, red is probably 10-12ga)
You can fuse to a smaller bus bar and put the smaller items in that bus or get a small fuse block.
Do you have something to cover these bolts with to prevent accidental shorting? A Company named Recoil makes covers you can put on the ring terminal themselves that would cover the nuts.


Looking closer, this looks like a fuse block? Should connect the smaller wires there.

Most 12 volt warm issues are caused by to small of wire size for the load or an improper/faulty conections.

How did you crimp the conections?
What size is your inverter?

Do you realize a 200 watt solar panel is woefully under sized for this system?]

I would be concerned about the 171F fuse temperature.

seneysolar said:

What size inverter?

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It is a 2000w pure sine from harbor freight. I should have included that, thank you!

SeaGal said:

Concerned about that temp. What current were your drawing? Suspect poor connection around the fuse, rather than the fuse itself, IMHO, but I'm no expert on 12V systems.

Only other comment would be to put insulated cover over the +ve bus bar and fuse, once the temp issues are resolved. Looks too easy to short between +ve and -ve with a wrench or similar on that end panel, which wouldn't be good if it was shorted the wrong side of the ANL fuse.

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Yes I definitely plan to cover them, keeping the switch off for now when I’m not testing. I have double and triple checked for loose connections, that was my first thought.

I was using a variable heat gun and space heater to keep it just under tripping my inverter, not a real world scenario but still wanted to test to the limit. The shunt showed 155a at 1.9kw

Austin92 said:

It is a 2000w pure sine from harbor freight. I should have included that, thank you!

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Honestly im more concerned about the 250 breaker than the ANL fuse. Those style breakers seem to have high failure rates.

The fuse is warm because its a choke point for current, but thats how they work, too much current for a period of time, fuse blows ( burns in half essentially). Temperature will be relative to its fuse rating.

Sennen said:

13.5 is a good charging voltage for 12v
Look into your battery spec for low cutoff. I would imagine in the 10.5v range
Fuses get warm, but not usually that warm. Check connection tightness.

What kind of amperage are you running through this whole system? That will tell you what size wire you need. If you're peaking at 300A and holding there, 2/0 might be a smidge too small.

This mostly looks good. A few callouts.

This tiny wire should be fused as a just in case. (I say tiny, white's probably 6ga, red is probably 10-12ga)
You can fuse to a smaller bus bar and put the smaller items in that bus or get a small fuse block.
Do you have something to cover these bolts with to prevent accidental shorting? A Company named Recoil makes covers you can put on the ring terminal themselves that would cover the nuts.
View attachment 203697

Looking closer, this looks like a fuse block? Should connect the smaller wires there.

View attachment 203700

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I would say the most this system would ever see continuous would be around 200a, saw Will’s video that recommended fuse/breaker 1.5 times expected continuous and to go up if there’s nothing directly at your calculation.

The small white/black is 8ga from my charge controller and has a breaker on it, it’s the 60a one. The red/black is 10ga and is the factory size that came with my Li time 20a plug in charger, the grey plug is factory too and in their instructions it says not to cut, splice, or change wire length any way. The little fuse block up top is for distribution of wires for things I add that’s 12v, it is the other set of 8ga coming off the bus bar and has a 100a breaker.

Do you still think I need to fuse a smaller bus?

Thank you for pointing out the recoil terminal covers

Here’s a little better lighting photo

2000 watts @ 12vdc gives you +-166 amps.

I would recommend checking out all your connections.

What did you have running when you got the 171F?
How long was it running?

Partimewages said:

Most 12 volt warm issues are caused by to small of wire size for the load or an improper/faulty conections.

How did you crimp the conections?
What size is your inverter?

Do you realize a 200 watt solar panel is woefully under sized for this system?]

I would be concerned about the 171F fuse temperature.

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This is the tool I’m using to crimp, running it down with an impact, not by hand. My inverter is 2000w.

I am aware my one 250w panel isn’t enough, that is why I made sure to show that it’s a 50a charge controller dc-dc with mppt. I’ll have plenty of charger left for 3, maybe 4 panels in the end as money allows me to add them and if there is a storm that knocks out the power for a few days I can run the dc-dc hook up out to my vehicle when the panels aren’t keeping up. Vehicle back up was the main reason for not going 24/48v, don’t have room for many panels with out making mowing or turning around a nightmare.

I too am concerned about the fuse temperature, it was the reason I made this post. I will probably never run the system that hard again but still like to know it’s safe if I have to.

seneysolar said:

Honestly im more concerned about the 250 breaker than the ANL fuse. Those style breakers seem to have high failure rates.

The fuse is warm because its a choke point for current, but thats how they work, too much current for a period of time, fuse blows ( burns in half essentially). Temperature will be relative to its fuse rating.

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Yes, the breaker did get warm also. Is there a cooler safer way to have short circuit protection?

Partimewages said:

2000 watts @ 12vdc gives you +-166 amps.

I would recommend checking out all your connections.

What did you have running when you got the 171F?
How long was it running?

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I have gone over my connections many times, that was my first thought too. I was using a space heater and variable heat gun so I could dial right up to the limit of the inverter to test for things like this. They ran for a half hour or so pulling 150-170a

Austin92 said:

Yes, the breaker did get warm also. Is there a cooler safer way to have short circuit protection?

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Not without spending $$$. Personally i like ANL fuses for high current low voltage stuff. Although id use Eaton / Bussman brand, hold one in your hand and the difference is clear.

Best way to find out if it's the fuse is to remove it and run your test without a fuse in place (temporarily, of course) bolt right to the battery. If nothing gets hot, there's your answer.

I believe torque spec on the mrbf is 110 inch pounds. Not sure about battery

seneysolar said:

Not without spending $$$. Personally i like ANL fuses for high current low voltage stuff. Although id use Eaton / Bussman brand, hold one in your hand and the difference is clear.

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That is something else I had thought about doing is ordering a name brand quality anl fuse but I didn’t think that would be the answer to everything. Are there any breakers up to this task? I really like being able to use them as on off switches if current is low.

Someone else mentioned the style I have notoriously go bad…

Fuses are better than breakers for lithium short circuit protection. Breakers can weld closed

Sennen said:

Best way to find out if it's the fuse is to remove it and run your test without a fuse in place (temporarily, of course) bolt right to the battery. If nothing gets hot, there's your answer.

I believe torque spec on the mrbf is 110 inch pounds. Not sure about battery

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Will definitely have to try that! What is the mrbf?

Sennen said:

Fuses are better than breakers for lithium short circuit protection. Breakers can weld closed

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Does that include lower amperage breakers?

Austin92 said:

Will definitely have to try that! What is the mrbf?

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Getting threads confused on my phone. Disregard

Austin92 said:

Will definitely have to try that! What is the mrbf?

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Ok. On desktop now. Definitely try to bypass the fuse. Can try to bolt that lower lug to the top one and see if any issue arise. As your thermometer was on the fuse at 175 (which is instant skin damage) I'm betting it's the fuse itself. A good holder and good fuse combo for that kind of fuse is about $80 for both.
Holder https://www.amazon.com/dp/B001VIVWAW
Fuse https://www.amazon.com/dp/B0026HGMI4 (This is ANN, will pop right at 300)

Sennen said:

Ok. On desktop now. Definitely try to bypass the fuse. Can try to bolt that lower lug to the top one and see if any issue arise. As your thermometer was on the fuse at 175 (which is instant skin damage) I'm betting it's the fuse itself. A good holder and good fuse combo for that kind of fuse is about $80 for both.
Holder https://www.amazon.com/dp/B001VIVWAW
Fuse https://www.amazon.com/dp/B0026HGMI4 (This is ANN, will pop right at 300)

View attachment 203851

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I didn’t know about the 2 different types of fuses, should I be using the ann over an anl?

Austin92 said:

I didn’t know about the 2 different types of fuses, should I be using the ann over an anl?

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ANN satisfies code. ANL isn't a limiter per se. ANN is.

Sennen said:

ANN satisfies code. ANL isn't a limiter per se. ANN is.

https://up.codes/viewer/texas/nfpa-70-2023/chapter/7/special-conditions#706.31_(D)

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Code like that is way over my head, I’m very mechanically inclined and familiar with 12v stuff from the automotive world but expert electricians blow my mind lol.

I did run about a 45 minute test pulling at least 120a the entire time, averaged 140a, saw spikes at 180a with the battery bank lead bolted to the switch input bypassing the fuse, nothing got over 100-105 until the input of the 250a breaker to the inverter, it reached 155F but the output never broke 130F

Sorry for the novel

Let me count the ways you could have issues:

1. Mounting it all in wood - appears to be partical board shelf. Bad idea - buy a metal/wire shelf that is strong enough for you to stand on. More than one post in the "Up in smoke... learn from my mistake!" forum started with partical board shelves. Put the batteries on a lower shelf, cut a piece of Durock cement board like they lay tile with to mount everything else on. Nothing flamable touching any part of it.

2. Using an ANL fuse inline with 4 parallel batteries - should be a class T - lookup AIC

3. With 4 in parallel you should use a pair of bus bars, 600amp rated - 400 plus 20% is 480. Nearest size is 600amp. Make sure they aren't cheap no-name. If you insist on running wires instead of bus bars, put a 125a MRBF fuse and holder on the positive post of all batteries.

4. Those breakers - if they aren't blue sea or eaton or quality they will likely have a firey fail.

5. This is opinion - that sort of hammer crimper is really only intended as an emergency. To do a proper crimp you need a 2lb sledge and anvil or solid surface. It takes a pretty hard hit. If the lug bends in the process the lug is to thin a metal. The right lug is thick walled to use in these.
Get a quality hydraulic crimper (temco or good brand, not the $40 version on amazon or from harbor freight) or order cables to length fron windy nation. This isn't opinion - if you crimp cables and it leaves wings the die size is incorrect or the lugs aren't the right specs. A lot of the cheap ones are marked in AWG and are actually metric. To pass an inspection the wire size must be imprinted in the metal of the crimp.

6. What brand and type of lugs did you use? Many of the cheap ones on amazon are thin crap. Do they have UL and size listings on them? Selterm, temco, Ancor, or marine rated lugs. If you use the cheap crappy ones most of the time they leave wings from not fitting the crimper and wire correctly.

7. I would buy enough rubber boots to cover the ends of every cable. Exposed metal is asking for a short.

8. Did you use any anti-oxide compound on all your connections? If not order a can of No-Ox-ID and put a thin coat on all connections. It keeps corrosion at bay and will cut through any lite oxide coating present on the battery terminals. No-ox-id is conductive dark colored grease. It is not the white stuff in the tube manufactured by Ideal.

9. Every wire in your system should be fused. Either inline or preferably at the point closest to the power source.

10. Try not to stack lugs and terminals. If you must biggest goes closest to the bus bar. And don't stack more than 2 high. Make sure to ONLY use washers. Not saying you are as I can't tell from the pictures.

11. If any part of your system is to warm to touch and hold your hand on, you are doing something wrong.

12. If this is in a living space get a battery powered smoke detector that is the ionizing variety. That will alarm based on smoke if something gets hot. Even if you can't see the smoke. And if there is actually a fire it will alarm as well. The standard type smoke alarm only alarms on smoke breaking an infrared beam inside it, so the smoke has to be pretty thick. The ionizing ones cost about $30 verse $10 but are well worth it.

ideally put this in the garage and run an AC cord into the house through a hole in the wall. Seal around it. Garage walls are generally required to have a 4 hour burn time before the fire can get into the living area.

What kind of cable are you using? There are many kinds and temperature ratings. Pretty much all of your cable should be welding wire 105c rated.

You may think the fuses and nothing flamable is overkill but the math shows - if you short a wrench across one of the batteries - all 400amps will cross through it. A MRBF on the post takes 0.01 to 0.1 seconds to blow. In that time the wrench will hit around 145F in 0.1 seconds and if not corrected the wire insulation melts in around 2 seconds. In around 5 minutes the wrench is red hot and melts. This assume 2/0 welding wire between the batteries. And it assume the BMS limits current to 100a per verse just shutting down. BMS control current by manipulating MOSFETs to turn them off and on, and there is a chance for them to fail shorted until they burn open.

So if you have fuses the most likely outcome is you pop all 4 of them because of how they are wired. If you switch to bus bars you put a MRBF/class T at the bar end and depend on the BMS to shut down current on one battery. Drop that wrench or otherwise cut the wire and you pop 1 fuse.