Combine lithium battery bank with AGM bank?

[John61CT]

"Central hub" thread for similar topics, powerpacks usually too small for full-fledged House banks, but fine for recharging electronic gadgets.

https://vanlivingforum.com/showthread.php?tid=23546

 

[kllcbosmetris]

All depends on the design of the lithium battery and its chemistry. and sure it has way higher discharge rate than lead, for the amp hour rating of the battery, but not for the price. I can get a 35 amp hour battery to discharge 300 amps no problem. sealed agm deep cycle too. and that is only 135 bucks. A lithium iron phosphate 100 amp hour battery can discharge 100 amps usually (some more some less, depends on design, which means individual discharge rate of the cells). And that battery would cost 899 bucks+, usually 1200 bucks. No comparison.

Kodiak can be used for house loads. check it out. and its a lithium ion. panasonic cells I believe.

and yeah of course, you would never ever mix the batteries!! One would charge way to fast after first large discharge taken over by the lithium because of low resistance. But if you have a battery charger separating the lead acid, its totally fine. Really depends. Its totally possible to use both and still isolate them. Takes a bit of work. Unless you use the kodiak. It kicks butt. Hook lead acids straight to it. has its own charging and discharging circuit for the lead acid maintenance. its cool!

Can you clarify something for me --

I thought about an extended Kodiak setup (Kodiak + AGMs) but one YouTuber said because the AGM is only dischargable to 50%, once you couple an AGM with a Kodiak Lithium, it removes the advantage of being able to discharge the Kodiak until 20% left. Is that true? When you couple Kodiak with an AGM, should you stop discharging the system once you hit 50%? Do you know if Kodiak has a charge separator? If you couple Kodiak with an AGM, which one of the batteries is used first? Do they go down simultaneously? If so, adding AGM removes the lithium 80% discharge advantage, am I wrong?

 

[John61CT]

Different chemistries should not be paralleled in use.

Yes while charging, but odds are good what is the optimum charge profile for one chemistry is not for the other.

Just as an example, a good quality AGM battery requires a charge rate of .4C for longevity.

So 300AH bank, you should have *minimum* 60A charger, 120A would be much better.

Have a look for the max continuous amps output of the charger included with the Kodiak.

 

[willprowse]

Can you clarify something for me --

I thought about an extended Kodiak setup (Kodiak + AGMs) but one YouTuber said because the AGM is only dischargable to 50%, once you couple an AGM with a Kodiak Lithium, it removes the advantage of being able to discharge the Kodiak until 20% left. Is that true? When you couple Kodiak with an AGM, should you stop discharging the system once you hit 50%? Do you know if Kodiak has a charge separator? If you couple Kodiak with an AGM, which one of the batteries is used first? Do they go down simultaneously? If so, adding AGM removes the lithium 80% discharge advantage, am I wrong?

Great point! Yes that is unfortunate. And the agm's that are attached do not charge all the way. Not ideal for large discharge application I suppose. It sure is great for beginners though. Charges the agm's at 30 amps which is nice. And I doubt that most people would ever discharge to 20% if they have some agm's hooked up to it. But great point!

 

[willprowse]

Different chemistries should not be paralleled in use.

Yes while charging,  but odds are good what is the optimum charge profile for one chemistry is not for the other.

Just as an example,  a good quality AGM battery requires a charge rate of .4C for longevity.

So 300AH bank,  you should have *minimum*  60A charger,  120A would be much better.

Have a look for the max continuous amps output of the charger included with the Kodiak.

Yes great point

 

[Zardor]

You guys are some serious solar nerds - I'm envious. Anyhoot, since I started this thread let me share what I've done. It may amuse some of you and maybe help, those like me. I purchased a cpap battery, it worked for 3 days great and then died. I took it back, they ran all kinds of test to figure out why and couldn't. So I paid 100 bucks for my units specific dc cord. And now life is good. With the inverter it was pulling 70 to 100 amps a night. I couldn't afford that and it put me in a scaredy place. Now with the dc cord I'm pulling 30 ish amps a night, which is no big deal. I can watch tv, or work on the computer at night. For pretty much as long as I like with no issues. My setup is working now as intended. Stress gone. Thank you all who took the time to be read and comment on this thread.

 

[John61CT]

No such thing as "amps per night" or per any time unit.

If you mean AH (amp hours) that makes sense, but wow that's a lot of energy.

 

[Zardor]

Given the conversation, it was assumed, but your right. I'm now using 30 ish "amp hours a night vs 70-100 amp hours.

 

[John61CT]

Definitely an improvement.

Other models (maybe less powerful) must consume much less, pretty sure other users of cpap machines were getting by with batteries under 100AH?

IMO the minimum size long-lasting true deep cycle bank is those Duracell FLA GCs, at 200+AH anyway.

But those sort of mission-critical consumption numbers imply minimum of 200W solar, and/or a small gennie depending on season, weather etc

 

[kllcbosmetris]

You guys are some serious solar nerds - I'm envious.  Anyhoot, since I started this thread let me share what I've done. It may amuse some of you and maybe help, those like me. I purchased a cpap battery, it worked for 3 days great and then died. I took it back, they ran all kinds of test to figure out why and couldn't. So I paid 100 bucks for my units specific dc cord.  And now life is good. With the inverter it was pulling 70 to 100 amps a night. I couldn't afford that and it put me in a scaredy place. Now with the dc cord I'm pulling 30 ish amps a night, which is no big deal. I can watch tv, or work on the computer at night. For pretty much as long as I like with no issues. My setup is working now as intended. Stress gone. Thank you all who took the time to be read and comment on this thread.

What kind of CPAP? ResMed? Where did you get the DC charger?