Is 40A Fuse enough for SOK 24v (2 x 12v) 206Ah ??

[Alberta Off-Grid]

I'm new to solar and I live off-grid... I've chosen the following set-up :

2000Watt, 24v Off-Grid Solar Setup (with the exact components on Will's site)

I've purchased two SOK 12v 206Ah batteries. Do all the 40Amps fuse, charge controller, Inverter stay the same for 206Ah as opposed to the 100Ah on Will's set-up?

Also, I'm running my generator every second day (for laundry and bigger appliances) and I would love to top up the batteries when the generator is running. Would a simple 12 volt battery charger from Walmart or Canadian Tire work? What's the best and simplest battery charger for my two SOK Lithium Batteries.

Where do I connect the charger, can I connect directly to the battery terminals?

Thanks, this is all new to me...

 

[HRTKD]

Size the fuse for the loads. 2000 watt load at 24v is 83 amps, not taking into account inverter inefficiency or surge. So 83 is the bare minimum for the fuse just downstream of the battery.

No, a cheap charger isn't going to work for a LiFePO4 battery. Look at the RV AC-DC converters that have a LiFePO4-specific charge profile.

 

[Alberta Off-Grid]

Thanks for the fast reply. Will uses a 50 amp circuit breaker downstream of the battery and his solar charge controller is 40 amp. His system uses 12 volt batteries with 100Ah, so I need to go higher than 83 amps for 200 Ah batteries?

 

[Alberta Off-Grid]

I'm starting to understand things a little better. How many solar panels, or should I say, how many watts of solar should I consider for a 40 watt solar charge controller?

 

[Hedges]

Thanks for the fast reply. Will uses a 50 amp circuit breaker downstream of the battery and his solar charge controller is 40 amp. His system uses 12 volt batteries with 100Ah, so I need to go higher than 83 amps for 200 Ah batteries?

You don't need a larger fuse on account of higher capacity 200 Ah battery vs. 100 Ah.
You may need a larger fuse if you draw more current.

If Will has a 40A charge controller, then 50A fuse is ideal for that part of the circuit, it is 25% larger than maximum continuous load to avoid nuisance trips.

As HRTKD says, if you have a 2000W inverter and 24V battery, current draw is over 83A. Probably up to 100A. So a 125A fuse would be appropriate (25% larger). Wire needs to be large enough for 125A, maybe larger to reduce voltage drop if a long run.

Type of fuse matters, because a lithium battery can deliver quite a few thousand amps into a short. Fuse may cost $30 to $50, not $5.

I'm starting to understand things a little better. How many solar panels, or should I say, how many watts of solar should I consider for a 40 watt solar charge controller?

You probably mean 40A, not 40W charge controller. Consider battery at 15V x 40A = 600W.
PV panels put out a bit less than their rating, so around 700W could fully drive the charge controller.

Question is, how many watt hours per day do you need for your loads?
How many effective hours of sun does your location get? (could be 7 hours summer, 2 hours winter.)
There are some tricks to put 1000W of panels on the charge controller and get more hours of operation rather than higher peak power.

Panels are cheap and batteries are expensive, so I try to keep battery as small as I can get away with and put in extra panels.

 

[HRTKD]

Thanks for the fast reply. Will uses a 50 amp circuit breaker downstream of the battery and his solar charge controller is 40 amp. His system uses 12 volt batteries with 100Ah, so I need to go higher than 83 amps for 200 Ah batteries?

No, you need to go higher than 83 amps because of your inverter. 83 is the absolute minimum. Even at that, if you pull 2000 watts out of the inverter, you could blow the fuse.

Let's say your inverter is 85% efficient. That means it needs 15% more amps to generate 1 amp. Take the base 83 amps x 1.15 and you get 95 amps. If you pull 2000 watts out of the inverter, then that will be 95 amps out of the battery. Many inverters will allow for quite a few more amps in a surge. The 95 amps does not take into account the surge. If you don't figure this into the size of the fuse you could blow a fuse.

 

[Alberta Off-Grid]

So this system wouldn't work? I don't see an 83 or 95 amps fuse anywhere? This is Will's 2000 Watt, 24 volt system and he uses a 40A charge controller. I was planning on copying it exactly with two 12v 200Ah batteries. I'm thinking of maybe 800 watt (4 x 195 Watts) Solar Panels and adding a battery charger (for my gas generator). Is the ATS a good battery charger or too expensive for my purpose?

 

[HRTKD]

The calculations I provided show the minimum number of amps for the rating. You would then take that and find the smallest fuse that is larger than that number of amps. However, recall that I said that the surge amps are not accounted for in my numbers. I don't know how many surge amps your inverter can handle.

Most inverter owner's manuals have a section on what level of over current protection to use. My Xantrex inverter manual was very good about that.

I don't know if this is the common implementation or not, but it seems like most people are using two levels of over current protection

Battery <--> Fuse <--> Switch <--> Common Bus Bar <--> Circuit Breaker <--> Inverter

My Class T fuse is quite expensive. The circuit breaker is about half the cost of the Class T fuse.

 

[Just John]

So this system wouldn't work? I don't see an 83 or 95 amps fuse anywhere? This is Will's 2000 Watt, 24 volt system and he uses a 40A charge controller. I was planning on copying it exactly with two 12v 200Ah batteries. I'm thinking of maybe 800 watt (4 x 195 Watts) Solar Panels and adding a battery charger (for my gas generator). Is the ATS a good battery charger or too expensive for my purpose?

View attachment 38055

I assume (Will doesn't say) that the ATS is an automated transfer switch, it certainly isn't a charger. Victron makes a solid 24v charger with a lithium profile, about $176, but only 12 amps. Once you are in that price range you might get a Riden power supply that puts out 18 amps and is far more flexible for $200. Likely better off with the Victron though, less chance to set something wrong and mess up the batteries. I am sure there are cheaper ones out there, I just haven't been looking for cheap. I know NOCO makes one that also puts out about 12 amps, but it is like $220 and not even close to the quality of the Victron.

 

[Hedges]

So this system wouldn't work? I don't see an 83 or 95 amps fuse anywhere? This is Will's 2000 Watt, 24 volt system

The system will work without a fuse.
The problem is when it doesn't work (i.e. suffers a short circuit)

Look up videos of shorted cells and of overloaded cables.

 

[Just John]

The system will work without a fuse.
The problem is when it doesn't work (i.e. suffers a short circuit)

Look up videos of shorted cells and of overloaded cables.

Yes, I forgot to add, Will doesn't show a fuse in that picture, but further down he shows installing one to the inverter, but doesn't tell you what size. Indeed it will work fine without a fuse (until it doesn't).

 

[Alberta Off-Grid]

Thanks for all the good comments and suggestions. I will definitely use a decent size fuse according to my systems needs. I ordered Will's book, that should help me with wire and fuse sizes.

I'll definitely look into the Viltron for a battery charger, when my generator is running. Would you connect the battery charger directly to the battery posts?

 

[Hedges]

Blue Sea has a good assortment of fuses.
Key parameters include voltage high enough for your battery, and "interrupting capacity" high enough for what your battery could deliver into a dead short. That can be from 3000A (some car batteries) to perhaps 20,000A (which a lithium battery may be able to deliver; we only have estimated calculations suggesting that.)
Some of us use class T fuses with our batteries.

Fuses - Blue Sea Systems

Engineering high quality marine electrical components for safety, reliability and performance

www.bluesea.com

 

[HRTKD]

Would you connect the battery charger directly to the battery posts?

Depends on what type of battery you have. LiFePO4? No, the connection would be made before the BMS. Lead acid? Sure, wherever you want.

 

[Just John]

Thanks for all the good comments and suggestions. I will definitely use a decent size fuse according to my systems needs. I ordered Will's book, that should help me with wire and fuse sizes.

I'll definitely look into the Viltron for a battery charger, when my generator is running. Would you connect the battery charger directly to the battery posts?

Well, if you get the Victron, that's the only way you can connect one. It has two ring terminals on the ends of the wires.

Blue Smart IP67 Charger Waterproof - Victron Energy

The Blue Smart IP67 Waterproof Charger is the new professional battery charger with built-in bluetooth. Find a Victron Energy dealer near you.

www.victronenergy.com

https://smile.amazon.com/gp/product/B07TKN76V7/

https://smile.amazon.com/Victron-Blue-Smart-Charger-Waterproof/dp/B07FGFRMCX/

This looks like what Will has been using lately, it certainly will charge a battery faster and a very good brand.

https://smile.amazon.com/AIMS-Power-CON120AC1224DC-Converter-Battery/dp/B07N1K43NQ/

You must be very careful, here is an example of what NOT to buy

https://smile.amazon.com/Battery-Charger-Lithium-Anderson-Connector/dp/B07BPN9RVX/

Notice it says "Output voltage: 29.4V (For 7S Li-ion Battery)", this will overcharge your battery unless a BMS stops it.

 

[Alberta Off-Grid]

This is the battery (x2) that I was thinking of buying. The guy here in Edmonton, Alberta is restocked today...

SOK 12V 206Ah LiFePO4 Lithium Iron Phosphate Battery Pack​