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G’day, have an 80 series landcruiser with dual battery set up. My Aux is a
MSDP27D exide marine deep cycle which runs everything and is charged by car’s alternator and a 170 watt solar panel. I’d like to purchase a lithium battery and put it inside the cab (to charge phones, laptop, low sun days etc) My question is can my mppt 75/15 controller charge and monitor both a lithium and my agm? If so what settings? Also advice on which lithium appreciated. Cheers.
Hi,
Because lithium batteries and AGM batteries have different voltage characteristics as the SOC varies, you can't charge these batteries in parallel. Lithium batteries tend to have very low variation in terminal voltage over 80% to 20% soc, while lead acid have a significant voltage change. If you want to install a lithium battery for a second AUX battery, then this will need an independent charging circuit, either off the alternator, or from the house battery. If you just want to charge mobile phones, then a power bank would be the best option, with facility to recharge this from the house bank. As your existing battery is 105Ah, I would look at replacing this with a lithium battery of about the same capacity, you will be amazed by the difference...(80% DOD,95% charge/discharge efficiency cf 50% dod and 60% charge efficiency for lead)
Mike.
Thanks Mike. Both batteries under the hood are fairly new. Maybe I should just get a massive lithium power pack and recharge it when I have 240. Then when my Aux dies I’ll swap it with a lithium. Any ideas how my alternated would go charging one?
That depends on 2 things: 1) The type of Lithium battery, and 2) the regulated voltage of the alternator - whether it is internal voltage sensing or external.
Lithium batteries - some have a max cell voltage of 3.65V, some 4.2V see spec sheets. The 3.65V cells give better compatibility with Lead Acid voltage ranges (This is the type I use) Then 4 cells in series give you a max pack voltage of 14.6V This is compatible with a well regulated Alternator which should top out at 14.4V. Some however go to 15V so this should be checked in advance.
If the alternator has an external regulator, this can be used to control the output. You would also need to consider a BMS to monitor the state of the battery and balance the cells. Because of the sharp increase in cell voltage in the 95 - 100% region, it is easy to over voltage one cell in a pack.
Looking getting a
https://www.radioandelectronicsupply.com.au/product/12v-100ah-lithium-lifepo4-battery-m8-f12-sl4576b-just-arrived/ I have a dual battery with a pirahna 100 amp isolator running
supercrank Nx-120-7L
and a
MSDP27D exide marine deepcycle as an auxiliary
my auxiliary gets topped up by my solar panel via my
Can anyone tell me if i can put the above lithium into the auxiliary battery circuit?
