| Re: Check my electrical math- battery to inverter to Air Con [message #370345 is a reply to message #370334] |
Thu, 11 August 2022 08:07   |
 |
RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma:
|
Senior Member |
|
|
"It turns out this might all be moot- if my math is right i can get three hours of discharge at 70 amps if i use SIX Duracell GC batteries @ about $120 each.
For $700 I can get a 200 amp Lithium battery and discharge it at 70 amps for the same three hours.
I think we've crossed that line."
Dave,
You will find Lithium (LiFePO4 aka LFP) are a much better battery than Lead Acid (LA). You can charge them in a much shorter time, they give back almost as much energy as you put into them (read efficient) and their discharge curve is flatter and at a higher voltage, not to mention they are much lighter in weight.
You will love them!
A $700, 200 Ahr LFP might not be the highest quality on the market though, you get what you pay for. While you can (should) get all 200ahr out of the battery, you will get more charge cycles if you limit the depth of discharge (DOD) to something less 100%. Aiming for 80% DOD might be more realistic for the battery price point you are looking at.
You will also need a beefy LFP rated charger to recharge it, both from shore power and while driving. A 60A charger is going to take just over 3 hours to fully recharge a flat 200Ahr battery and unlike a LA charge cycle, a LFP battery will consume that 60A the whole time. While driving, I recommend a DC-DC charger to recharge from the vehicle alternator. These chargers take the vehicle power and transform it to the proper LFP charging curve and properly limit the current. On the other hand, a BIM combiner directly connects the alternator to the LFP battery for 15 minutes then disconnects for 20 minutes to let the alternator cool down (like a very slow cycle PWM regulator). While connected, the LFP battery will consume all the current the alternator can give and likely more than its rated for.
You might want to check out Will Prowse's solar forum for some good info on LFP batteries and charging. Also check his many videos on youtube.
https://diysolarforum.com/
Here is an excellent article on LFP batteries. It is written for boaters, but most info also covers RV applications.
https://marinehowto.com/lifepo4-batteries-on-boats
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
|
|
|
|
GMCforum
Search
Help
Register
Login
Home
