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Old 06-30-2020, 03:58 AM   #1
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Default Some Electrical Theory/Questions

So letís suppose Iím going to upgrade my electrical/battery/solar with the idea that in the near future I were to add a compressor fridge. Right now I have a single 100AH lifeline AGM battery and a 100W Renogy solar suitcase. The circuit running from my alternator to the house battery has a 40 breaker. I have no idea what the output of the alternator is.

It appears that c50AH is a common usage for, say, a 3-4cu. ft. compressor fridge which would mean that I would have one day usage on my current battery. So here are the questions:

1. What would be an optimal battery setup? Could I add 200-300 lithium and just dedicate that to the fridge?

2. Would my current alternator be sufficient to charge the lithiums and the AGM? I realize that Iíd have to have some system in place to alternately charge each and some system to monitor. Too bad I didnít buy the viltron 712 which monitors 2 batteries instead of the 700.

3. I know that my solar is insufficient to charge both systems. How do I calculate what to add? Or is it just better to upgrade alternator since Iíve seen some discussion in that direction.

4. Iím assuming that Iíd have to add a DC->DC charger to handle the multistage charging on the batteries?

5. Iíd have to check the gauge of the alternator to battery but am guessing that it would have to be upgraded?

One of the ďshortsĒ here is: what alternator and solar accommodations have to be made to adjust for the increased battery storage? Many of you have done this type of upgrade and Iím curious what you did. It might be that I just trash the Lifeline (hate to) or that additional AGM instead of lithium might be the route to go instead. The LifeLine is only a few years old. Would prefer some hybrid that would allow me to keep it until it goes but maybe this is stupid economics.

There are some basics here but if there isnít sufficient interest perhaps people could PM me instead.

Thanks, as always. glenn
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Old 06-30-2020, 04:28 AM   #2
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Originally Posted by GallenH View Post
So let’s suppose I’m going to upgrade my electrical/battery/solar with the idea that in the near future I were to add a compressor fridge. Right now I have a single 100AH lifeline AGM battery and a 100W Renogy solar suitcase. The circuit running from my alternator to the house battery has a 40 breaker. I have no idea what the output of the alternator is. Probably 40 amps is all you'll want to pull off your engine generator.

It appears that c50AH is a common usage for, say, a 3-4cu. ft. compressor fridge which would mean that I would have one day usage on my current battery. So here are the questions:

1. What would be an optimal battery setup? Could I add 200-300 lithium and just dedicate that to the fridge? 200Ah lithium batteries are what I installed (we have a Novacool 3100 compressor fridge). We drive nearly every day (no solar) and so we run whatever we want (including microwave off the 3000W inverter) and a full day is no problem. Could go two days without much problem, but that's about it. Add a day for each additional 100Ah lithium battery.

2. Would my current alternator be sufficient to charge the lithiums and the AGM? I realize that I’d have to have some system in place to alternately charge each and some system to monitor. Too bad I didn’t buy the viltron 712 which monitors 2 batteries instead of the 700. See 40 amp max draw comment above (unless you have an upgraded alternator).

3. I know that my solar is insufficient to charge both systems. How do I calculate what to add? Or is it just better to upgrade alternator since I’ve seen some discussion in that direction. More solar never hurts, but if you drive a few hours or run your onan genrator a few hours, you should get your lithum batteries up to nearly full.

4. I’m assuming that I’d have to add a DC->DC charger to handle the multistage charging on the batteries? Yes. It will protect both your engine alternator and your investment in lithium batteries.

5. I’d have to check the gauge of the alternator to battery but am guessing that it would have to be upgraded? My 4ga. factory wiring is good for my 40A DC to DC charger. I did not upgrade.

One of the “shorts” here is: what alternator and solar accommodations have to be made to adjust for the increased battery storage? Many of you have done this type of upgrade and I’m curious what you did. It might be that I just trash the Lifeline (hate to) or that additional AGM instead of lithium might be the route to go instead. The LifeLine is only a few years old. Would prefer some hybrid that would allow me to keep it until it goes but maybe this is stupid economics.

Check out others' "hybrid" installs here:
https://www.classbforum.com/forums/s...archid=1697049

There are some basics here but if there isn’t sufficient interest perhaps people could PM me instead.

Thanks, as always. glenn
See bold above.

Upgrading is pricey and does include upgrading all charging components (solar controller, alternator DC to DC charger, and Inverter/Charger).

Lithium batteries are $800-950 each for 100 Amp hours. You'd want two lithium batteries minimum like I did. A solar controller $150, DC to DC charger $200, and 3000W Inverter/Charger for $800-1300. Another $100 for a batter State-of-Charge monitor and another $150 for various cables, connectors, and fuses.

I did mine on-the-cheap with Renogy products and my own labor. $3000 in total just to extend available battery power by 2x, run the microwave on an upgraded 3000 pure sine wave inverter charger, and to reduce the charging time for the lithium batteries. A similar top-of-the-line upgrade with Battleborn and Victron components would be about $1000 extra, again with your own labor. Add another $2 grand for two more batteries and a really nice 400Ah upgrade. Yes, the price adds up fast.
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Old 06-30-2020, 11:11 AM   #3
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Going the cheaper route, I added one 105ah AGM to my system bringing the total up to 210ah. I put 300 watts of solar on the roof and most importantly, installed a quality battery monitor. Everything else remained the same. I always had plenty of juice to run the fridge because I knew exactly where I stood because of the monitor and also because of how I used the van. A sunny day would have the batteries topped off by noon or a drive to sightsee would replenish them enough for another night. Between the battery, panels, controller and monitor, I was in for under $1000.
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Old 06-30-2020, 12:25 PM   #4
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If you are OK with battery life now with one battery, 100 watts of solar, and no compressor frig, I would agree with keep it simple method mentioned above.


Adding one battery and 100-200 (200 preferred) watts of solar seems to be the most common method of covering compressor frig power use for most people moving to a compressor frig of moderate size. It seems to work very well without major issues unless you are a shade only type camper, and sun counts for this method. If solar isn't enough and you drive regularly that works, too.



I do think the alternator charging would need to be addressed in some manner if you increase the battery capacity by any means, as even two AGMs are going to be tripping the 40 amp breaker all the time until it fails.


You can either limit the current to coach from the engine with a b to b charger or split charge relay that limits output and/upsize the wiring for maybe 80 amps. What you decide may be decided as much by how big your alternator is as by what you want. It is best to stay at 40-50% or under on alternator output, IMO, to prevent heat issues with the alternator, so you can use that for a guide once you find out what alternator you have.
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Old 06-30-2020, 07:44 PM   #5
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Thanks for all of the great replies. I suspect I've been a bit lazy and that I should dig around the engine compartment for the alternator make/model etc.
That would, hopefully, give me some specs. I'm guessing, though, that there might be some limitation like "if you're now charging 400AH instead of 100AH you need a larger alternator?

Does putting a DC->DC charger between the alternator and the battery area give you the charging profile/stages necessary for AGM and lithium? I'm assuming those are totally absent on my old/97 setup and that the original battery just kept charging off the alternator at the same rate.

Do lithium batteries charge faster than AGM?

BTW: I don't have a generator and don't intend to add one.
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Old 07-01-2020, 01:34 AM   #6
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Originally Posted by GallenH View Post
Thanks for all of the great replies. I suspect I've been a bit lazy and that I should dig around the engine compartment for the alternator make/model etc. Correct. That is how I found out my alternator is 160 amps, not 145 amps like the manufacturer specs. I bought used, so it is possible it was replaced before I bought it.

That would, hopefully, give me some specs. I'm guessing, though, that there might be some limitation like "if you're now charging 400AH instead of 100AH you need a larger alternator? Exactamundo. Larger battery become impractical without the means to charge them rapidly.

Does putting a DC->DC charger between the alternator and the battery area give you the charging profile/stages necessary for AGM and lithium? Yes, if you buy a lithium-compatible DC to DC it will also have settings that are backwards compatible with AGM/GEL/FLOODED. The same backwards compatibility is generally true for Solar Controllers and Chargers that have lithium profiles.

I'm assuming those are totally absent on my old/97 setup and that the original battery just kept charging off the alternator at the same rate.

Do lithium batteries charge faster than AGM? Yes, but they are limited by your charging source and wire gauge. That is why I can charge my lithiums at up to 75 amps when plugged into 120 volt or charging off generator. But why I limit the engine alternator to 40 amps of charging to not exceed it's capability and factory 4 gauge wiring.

BTW: I don't have a generator and don't intend to add one. Go big on solar.
See bold above.
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Old 07-05-2020, 12:28 AM   #7
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I’ve charged in excess of 330 amps to my lithium batteries as I have simultaneous input from the second alternator, solar and shore power. When driving I can consistently get 280 amps for a whole hour driving at 50 mph. I did that as a test on the Natchez Trace Parkway that ended when fully charged. I have an 800ah lithium battery bank. I have a 4.0 wire from the second alternator (Delta) to the batteries.
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