Can I use a DC charger as a trickle charger in an acid to lithium battery bank?

[Trexal]

I am trying to get the best of both worlds. Every time I switch on fridge, tumble dryer, or washing machine, I know my deep cycle Acid batteries take a beating from the high power draw and reduce their life expectancy.

I want to use a DC-to-DC charger between a large battery bank of Acid batteries and one Lithium battery. The inverter to be wired to Lithium. So the chain as follows:

Panels -> Solar Charger -> Acid Bank - > DC to DC Charger -> Lithium -> AC Inverter

Why? My thinking is that the Lithium cells would absorb the very large but relatively short power draws, while the DC 2 DC charger would then trickle charge the Lithium from the deep Acid cells.

I'm thinking this would allow me to get a very large battery storage with better life expectancy but for less than the cost of going all Lithium.

Thoughts?

 

[Bobert]

When you charge lead acid batteries you have significant efficiency losses in the charging and discharging of them in addition to the waste incurred by the fact that only a small portion of your solar arrays output will be able to be used to charge the batteries to get them from 90 to 100 percent (this needs to be done frequently or the batteries life span will be shortened. In addition to another efficiency loss I believe a dc to dc charger would require your lead bank to be higher voltage than the correct charge voltage of your lifepo4 bank.

My opinion is that you will get better results short term if you take the funds for the lead acid bank and the dc to dc charger and put it into as large of an lifepo4 battery bank as you can afford. Long term there is no question lifepo4 is the more cost effective.

 

[OzSolar]

I am trying to get the best of both worlds. Every time I switch on fridge, tumble dryer, or washing machine, I know my deep cycle Acid batteries take a beating from the high power draw and reduce their life expectancy.

I would offer that lead acid batteries are quite well suited for doing this. Perhaps even better suited than ~lithium because the BMS will limit the peak amps that the battery can deliver.

I would focus my efforts on making sure I was properly maintaining the batteries as that will likely lead to the best life for them. I've replaced a fair amount of big lead acid battery banks over the years and my anecdotal observation was that usage had almost nothing to do with thier early demise and that what killed them was being poorly maintained. Every bank that I've been around that was well maintained had an impressive life.

 

[Bobert]

I would offer that lead acid batteries are quite well suited for doing this. Perhaps even better suited than ~lithium because the BMS will limit the peak amps that the battery can deliver.

I would focus my efforts on making sure I was properly maintaining the batteries as that will likely lead to the best life for them. I've replaced a fair amount of big lead acid battery banks over the years and my anecdotal observation was that usage had almost nothing to do with thier early demise and that was killed them was being poorly maintained. Every bank that I've been around that was well maintained had an impressive life.

OzSolar is right a properly sized lead acid battery bank will handle heavy loads with no problem and have a very respectable life span if properly maintained. The issue I have here in the northeast is keeping them properly charged when we have many cloudy days in the fall and winter. It required hours of generator time every cloudy day and we have a lot of those and often 3 or more in a row. The costs and time of keeping my bank properly maintained was one of the main reasons I ended up switching to lifepo4. If the space and weight limitations were not so restrictive for a mobile application I think I could have made it work with a larger bank.

 

[Vigo]

This actually sounds like a possible use case for directly paralleled (at least part time) lead and lithium.

Basically, the lithium will supply the load first until the voltage of the lithium drops to the lead’s voltage, at which point they will drain together. The lithium will also charge first. I have done this for a couple of months this year although i got enough lithium to no longer do it. Plenty has been written about it elsewhere. It might be something to consider.

 

[ghostimage]

Hi. I'm trying to achieve something like that. I have an aging Agm bank. And just put together Lifepo4 battery. But my approach is a bit different. I'm going to use my lifepo4 as a main power and tap into agms as a suplimet. I'm not using dc to dc. But rather two parallel systems one agm othe lifepo4 both charged by solar and tied to an inverter. (Small sister, big brother) lifepo4+sw4048 feeding ac to XW6848Pro+agm as a grid and passed through to loads. When the loads exceed 10a agm helps with the rest. At night sw support everything pretty much and floats Agm. So agm bank just sits there topped of most of the time and lifepo4 does majority of the day to day lifting. Agm helps with heavy loads here and there. I'm still working on it. But so far it seems like it will work.