Need help planning for Solar and DC to DC

Jon R said:

Even with the CPAP machine at 2 plus amps continuously all night plus the fridge and other loads, i think your usage in a 24 hour period won’t exceed 50 amp hours.

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^^^^ Jon R, I’m starting to buy components - what would your recommendation be for positive (+) cable size from the house battery positive post (and fuse size) out to the positive bus bar and loads), given your reply above? Wondering if the #6 is too small?

(As we discussed earlier for the dc to dc charger itself it will be the #6 wire and a 50A fuse, (thank you for that!) but I wasn’t sure on a fuse size for just the house battery even though it has built in 200A BMS)

I saw a post that said fuse size should be max amp load plus 25% but I know that my estimated 50A hours consumption in a 24 hour period won’t be all at the same time.

I didn’t mention, I’ll be using an ANL style fuse block to accommodate the cable and lug terminals.

Here’s a link to the battery I bought. I decided on it by pouring over manufacture specifications and buyers reviews and ratings. I wasn’t a member of the Wander the West forum yet or I would have asked. I know you had questions about it, and honestly I’m still trying to understand all the built in features. The internet reviews (top 10 LiFePo4) seem to change all the time, I really hated breaking the bank on some of the ones that were deemed best. I guess I’ll know in time in how it functions for my purposes.



Thanks, Glenn

The 50 ah was an estimate of the worst case total battery energy you would use in a day. (Amp-hours technically needs to be multiplied by battery voltage to get energy, but everybody in the automotive/rv industry uses it as an analog for energy based on the assumption of a battery voltage.) That estimate of total energy usage doesn’t tell you anything about your peak electrical current or highest constant current, which are among the primary considerations in sizing wire and the primary consideration for sizing circuit protection (fuses or circuit breakers).

To determine maximum constant current, add up the amps drawn by all of the loads you think you would ever possibly use at the same time. Going back to your post #7 in this thread where you listed your loads, I have some questions before we total the loads.

1) Do you use your electric filet knife at the same time as your CPAP machine? If so, can you please post pictures of that?

2) Do you use your filet knife in cold weather in conditions where your tank or battery heater blankets may be running?

Jon R said:

1) Do you use your electric filet knife at the same time as your CPAP machine? If so, can you please post pictures of that?

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?? Not that I’m aware of…… I’m a pretty light sleeper.

Jon R said:

2) Do you use your filet knife in cold weather in conditions where your tank or battery heater blankets may be running?

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I don’t ice fish yet, although I would like to go up North and give it a go. So that’s a No for now?

Jon R said:

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To determine maximum constant current, add up the amps drawn by all of the loads you think you would ever possibly use at the same time. Going back to your post #7 in this thread where you listed your loads,

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I will try to figure out what some of the loads are that I ‘might’ add. A 12V television and small microwave to “reheat” for torrential downpours.

I guess the beauty of the design is the positive and negative cables to their respective bus bars will be relatively short and easily upgraded as well as changing to a larger fuse on an ANL fuse holder.

I’ll try to get a comprehensive list of the loads for “need” and “maybe want”

Thanks!

Glenn said:

?? Not that I’m aware of…… I’m a pretty light sleeper.


I don’t ice fish yet, although I would like to go up North and give it a go. So that’s a No for now?



I will try to figure out what some of the loads are that I ‘might’ add. A 12V television and small microwave to “reheat” for torrential downpours.

I guess the beauty of the design is the positive and negative cables to their respective bus bars will be relatively short and easily upgraded as well as changing to a larger fuse on an ANL fuse holder.

I’ll try to get a comprehensive list of the loads for “need” and “maybe want”

Thanks!

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TV will be a small load. A 1200 watt microwave and your 800 watt coffee maker will be large loads that you power from an inverter wired directly to the battery (not via your fuse panel) because of its high current demand, so it’s not relevant to sizing the wire to your fuse panel.

I was so intrigued by what you would look like filleting a fish while wearing a CPAP mask that I forgot to ask if your fillet knife is 120 vac or 12 vdc.

Assuming your fillet knife is 120 vac, it looks like your power draw with all the dc loads on is under 500 watts, or about 40 amps. Your peak surge loads from starting the water pump, fridge, or fan may be a couple of additional amps. So let’s say 48 amps for some margin. Then add 25% per the general practice, so size for 60 amps. (That really adds double margin for the brief peak current, but margin is good.).

6 awg is adequate for 60 amps from a wire heating standpoint, and good for short runs with less than 3% voltage drop. Since you already have loads of margin in that calculation, a 60 amp fuse at the camper battery would adequately protect the wire without nuisance trips. So would an 80 amp fuse (that’s what I have on my 6 awg wire at the truck battery and the camper battery).

Your inverter that powers your various 120 vac loads would be wired directly to the battery (via the shunt) because it will draw very high current. A 2000 watt inverter operating at full load will draw 170 amps. That’s going to need 2/0 cable. Vic has a setup like that and would be a better source of advice for wiring practices for a large inverter installation.

I would suggest you consider a smaller inverter if all you want to run is a small microwave and your coffee maker. If you have an 800 or 900 watt microwave instead of a 1200 watt one, a 1000 watt inverter would do the job, and would only require 4 awg wire for its roughly 80 amp current draw.

Jon R said:

Assuming your fillet knife is 120 vac, it looks like your power draw with all the dc loads on is under 500 watts, or about 40 amps. Your peak surge loads from starting the water pump, fridge, or fan may be a couple of additional amps. So let’s say 48 amps for some margin. Then add 25% per the general practice, so size for 60 amps. (That really adds double margin for the brief peak current, but margin is good.).

6 awg is adequate for 60 amps from a wire heating standpoint, and good for short runs with less than 3% voltage drop. Since you already have loads of margin in that calculation, a 60 amp fuse at the camper battery would adequately protect the wire without nuisance trips. So would an 80 amp fuse (that’s what I have on my 6 awg wire at the truck battery and the camper battery).

Your inverter that powers your various 120 vac loads would be wired directly to the battery (via the shunt) because it will draw very high current. A 2000 watt inverter operating at full load will draw 170 amps. That’s going to need 2/0 cable. Vic has a setup like that and would be a better source of advice for wiring practices for a large inverter installation.

I would suggest you consider a smaller inverter if all you want to run is a small microwave and your coffee maker. If you have an 800 or 900 watt microwave instead of a 1200 watt one, a 1000 watt inverter would do the job, and would only require 4 awg wire for its roughly 80 amp current.

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Jon R said:

I would suggest you consider a smaller inverter if all you want to run is a small microwave and your coffee maker. If you have an 800 or 900 watt microwave instead of a 1200 watt one, a 1000 watt inverter would do the job, and would only require 4 awg wire for its roughly 80 amp current draw.

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Sounds like a solid plan?. After all, hopefully most of my time is spent on the water, in the woods, ot around a campfire?