Turtle and electronics

[Billy The Impaler]

I hope you find time to address this. You seem to be the electrical system guru.

The van owner said I could take out the passenger seat. There's already a heater under there that doesn't work. Hopefully that will get repaired. Once the seat, which sits on those white metal pedestals, is gone, I'd like to put 2 lithium batteries and my chest style refrigerator there. A YouTube expediter says his 2 batteries will run his fridge for days between recharging them.

For next summer, one of those Cool Breeze AC units with 2 batteries. I partition off the space behind my bed with curtains so I'll be cooling a small space.

Anyway, I don't know much about electrical stuff. What do I need to do to install those house batteries? What kind of cabling from the van battery? I know the terms in series and in parallel, but really, the terms are all I know.

I'd like to avoid lugging a generator around but I guess I would if I had to. Suppose I could put it up front by the fridge and batteries.

I'd appreciate any guidance you could give.

 

[danthewolf00]

Look for eclipse blackout curtains to help with heating and cooling.

 

[Turtle]

What do I need to do to install those house batteries?

Some way to strap, bolt, latch or frame them down so they won't move regardless of how bumpy the roads are.

What kind of cabling from the van battery?

First thing you'll need is a battery separator. It sits between the starting battery and the house bank. It ensures your starting battery is completely isolated from the house bank so the house appliances don't drain down and kill the starting battery.

You want thick cables (Flex Cable or welding cable instead of battery cable), at least AWG 2, may AWG 0. Thicker means less voltage drop, but also thicker is more expensive, especially for the cable lugs (you'll probably want Panduit lugs made especially for flex cable).

I know the terms in series and in parallel, but really, the terms are all I know.

If your house batteries are 12 volt, everything will be in parallel (volts stay the same but capacity is increased). If you use 6-volt batteries, then series per pair of batteries (volts doubled (to 12) but Ah capacity stays the same). Two pairs of 6v batteries (4 batteries) would be series for each pair then parallel for the paired sets.

This was my battery bank under the bunk. Four 6-volt areal lift batteries (305 Ah each pair), marine bus bars, Main off switch, Class T fuses.

 

[Billy The Impaler]

Were those lithium batteries? The YouTube expediter said 2 lithium batteries would be all one needs to power a refrigerator for days without turning the key. And if the starting battery is isolated, it still recharges the battery bank off the alternator? Where did you run the thick cable from your engine compartment to those batteries? Did you have readout gauges somewhere to monitor the charge level?

 

[Turtle]

No, they weren't lithium batteries. If you can afford them, that's the way to go.

The battery isolator separates the battery bank and the starting battery as long as the voltage coming from the starting battery is less than about 13 volts. As soon as the alternator kicks in and the voltage rises above that, isolator combines the batteries so that the back gets charged.

The battery isolator has two large bolts with nuts. Two one bolt you connect a short cable from the starting battery, and the other bolt is the cable to the house bank.

I used a Xantrex Battery Monitor to keep track of the battery bank voltage, as well all amps in and all amps out.

 

[Turtle]

One thing I should add...it doesn't matter if the batteries are wet cell, AGM, lithium or Russet potato, it's all about amp hour capacity of the battery bank versus amp requirements of the appliances.

You need to know how many amp hours you'll draw from the battery between full recharges of the bank. You'll use more than you think, because you'll figure out new ways to use the batteries, plus you lose 10% on an inverter. So whatever you calculate, add 50% more to it. If you think you'll use 50 Ah in, say, a 24 hour period, it'll be 75 Ah. And you don't really want to draw down the battery much below 50% of the charge, so you'll need twice the battery capacity than you use between full charges.

Add up the number of Ah you'll use over a given time. If the fridge runs 12 hours over a 24 hour period, and draws 2 Ah per hour, that's 24 Ah. If a roof vent fan draws 0.8 amps per hour for 18 hours, that's 14.4 Ah.

Some applications will tell you the amp draw, some will say Watts. Just remember that amp x volts = Watts. So Watts / volts = amps.

If something draws 300 Watts, divided by 12 volts is 25 amps. If it's through am inverter that's 27.5 amps drawn from the battery due to the 10% loss. If you run that applliance for 5 hours, that's 137.5 Ah from the battery.

 

[LDB]

I love reading Turtle's technical posts. I don't understand half of it, but I enjoy them. Once you have your own vehicle look into an Onan 2800 Quiet generator. Mine fit in the spare tire well under the van. Quiet enough to sleep with it running and enough power for my roof a/c and 4' fridge. Only bad part is frequent oil changes.

 

[danthewolf00]

Ahh turtle and his technical post........my headache returns.

 

[Billy The Impaler]

I love reading Turtle's technical posts. I don't understand half of it, but I enjoy them. Once you have your own vehicle look into an Onan 2800 Quiet generator. Mine fit in the spare tire well under the van. Quiet enough to sleep with it running and enough power for my roof a/c and 4' fridge. Only bad part is frequent oil changes.

Yeah, half of it is all I understand, too, unfortunately.

 

[Billy The Impaler]

Are two 100 amp lithium batteries ok, or would that be insufficient?

 

[danthewolf00]

Are two 100 amp lithium batteries ok, or would that be insufficient?

100 amp hour ?

 

[danthewolf00]

Get a appliance voltage reader so you can plug them in a wall outlet and add them all together and then add in voltage loss with the inverter.

 

[Billy The Impaler]

Ah, so I guess amp hour, yes. I see them on Amazon in 4 packs for like $1200. But a YouTuber expediter I watch, I think he said 100 amp batteries. Just doesn't sound like enough. Don't think I'll be ruining a microwave, but a fridge for sure. He said he can run his fridge for a few days on his battery bank.

Also, if my starter battery dies, can I jump it off my battery bank, or would it have to be 12v for that?

 

[danthewolf00]

Nope you can use golf cart/ floor scrubber 6 volt batterys wired up as a 12 volt big battery bank and get even more amp hour.
The small set I used was 4 125 amp hour 6 volt....smaller than what turtle used but same brand. If you get a rv refrigerator that's made for car systems you can run alot longer....then down the road add solar panels.

 

[Turtle]

Also, if my starter battery dies, can I jump it off my battery bank, or would it have to be 12v for that?

If the starting battery is 12 volts, the house battery bank needs to be 12 volts, as well. Otherwise the alternator won't charge the battery bank.

Two 6 volt batteries wired together in series gives you one 12 volt battery. Four 6 volt batteries wired in series / parallell gives you one great big 12 volt battery.

 

[Turtle]

Don't think I'll be ruining a microwave, but a fridge for sure.

A fridge will use more amps than a microwave will. It's just that the amp draw from the microwave will be a really, really lot over a short period of time.

Let's say the microwave draws 900 Watts. 900 / 12 = 75 amps. Add 10% for the loss from the inverter, so 75 + 7.5 = 82.5 amps drawn from the battery. If you run the microwave for 10 minutes within a 24 hour period, that's 0.167 hours, times 82.5 is 13.785 amp hours removed from the battery over that 10 minute span.

If the fridge runs 18 hours over a 24 hour span, and draws 3 amps every hour of those 18, that's 54 amps removed from the battery.

There's also something called the Peukert Effect that factors in, especially with high amp draws. Basically, the faster you draw amps from the battery, the fewer amp hours the battery has available.

A 100 Ah battery is usually figured at a 5 amp draw for 20 hours. Or, how many amps the battery has at a 5 amp draw for 20 hours.

 

[Turtle]

I think he said 100 amp batteries. Just doesn't sound like enough. Don't think I'll be ruining a microwave, but a fridge for sure. He said he can run his fridge for a few days on his battery bank.

Your best bet is a 12 volt fridge designed for an RV, truck or a boat. Not a dorm fridge or an Igloo plug-in, but a $600 or so fridge designed to efficiently run on a 12 volt system. I started out with a very efficient down fridge/freezer, but in the end it was just too hard on the batteries. Ended up with (the older version of) the Dometic CFX3 35.

 

[Billy The Impaler]

A fridge will use more amps than a microwave will. It's just that the amp draw from the microwave will be a really, really lot over a short period of time.

Let's say the microwave draws 900 Watts. 900 / 12 = 75 amps. Add 10% for the loss from the inverter, so 75 + 7.5 = 82.5 amps drawn from the battery. If you run the microwave for 10 minutes within a 24 hour period, that's 0.167 hours, times 82.5 is 13.785 amp hours removed from the battery over that 10 minute span.

If the fridge runs 18 hours over a 24 hour span, and draws 3 amps every hour of those 18, that's 54 amps removed from the battery.

There's also something called the Peukert Effect that factors in, especially with high amp draws. Basically, the faster you draw amps from the battery, the fewer amp hours the battery has available.

A 100 Ah battery is usually figured at a 5 amp draw for 20 hours. Or, how many amps the battery has at a 5 amp draw for 20 hours.

So if I get 2 of them, I have 200 amps to work with, but I really only want to use about half, so figure 100. That's only 20 hours at 5/hour. And then I'd have to start the engine for whatever period to recharge them?

 

[Billy The Impaler]

Your best bet is a 12 volt fridge designed for an RV, truck or a boat. Not a dorm fridge or an Igloo plug-in, but a $600 or so fridge designed to efficiently run on a 12 volt system. I started out with a very efficient down fridge/freezer, but in the end it was just too hard on the batteries. Ended up with (the older version of) the Dometic CFX3 35.

I already have it. It's a chest style but has a compressor and freezer compartment. Says it has eco mode.

 

[Turtle]

So if I get 2 of them, I have 200 amps to work with, but I really only want to use about half, so figure 100. That's only 20 hours at 5/hour. And then I'd have to start the engine for whatever period to recharge them?

Correct. It'll take longer to recharge the house bank than you think, but at least with lithium batteries you don't really have to worry too much about making sure they are full recharged every time you charge them.