Creative use of AGMs after upgrading to lifepo4

[jt_retro]

Hey Folks

As the title suggests, I'll be replacing my 6 x AGM with a single lifepo4 battery soon.

Can anyone suggest any creative uses for these AGMs as some form of dump load?

The problem with LA is of course they will sulfate if left at a low SOC, so I can't think how I could design a circuit that would allow me to use these as a standby dump load.

Thanks!

 

[chrisski]

I don’t think anything practical can be done, otherwise there’d be tons of threads.

I almost kept ac12 volt lead acid battery when I upgraded to 24 volts to run the 12 volt loads, but opted or a 24 to 12 vdc converter. Keeping an AGM battery charged off a DC charger to run different voltage loads is the only thing have.

 

[45North]

Sell 'em.
Let someone else figger out what to do.

 

[jt_retro]

I was thinking....I could keep my agm battery bank topped up and on float permanently, to be used during a power outage. We don't really get power outages here, but never say never!

I could use just one of my cheap 240v amazon chargers to keep it on float, and then use my renogy dc dc charger to recover if necessary?

 

[Rednecktek]

Use them to power the heating pad circuit of your LiFe battery bank in the cold weather?

Mail them to me?

 

[12VoltInstalls]

Can anyone suggest any creative uses for these AGMs as some form of dump load?

If this a fixed installation (home) I would be inclined to stick one of the 12V AIOs on them with 400W of panels and power your daily continual loads. Solar would recharge the batteries and power things most of the day and battery into the night. Set it to disconnect batteries and use grid once depleted but not grid-charge batterie; and at sunup the solar kicks in again.

That won’t save you any money but it will reduce your grid usage.

 

[jt_retro]

Unfortunately I don't have the space for another solar system. The AGMs are currently in use with my solar system (to be replaced by a lifepo4)

The idea for a heating circuit is interesting. Might be good to keep an ambient temp during the deep winter.

 

[12VoltInstalls]

Might be good to keep an above ambient temp during the deep winter.

 

[Shinebox]

I have the same situation, and I’ll be using my AGMs to provide power to a shed I have on the property. Small solar array and small inverter.

 

[wattmatters]

I was thinking....I could keep my agm battery bank topped up and on float permanently, to be used during a power outage.

That's pretty much the life my lead batteries have, aside from providing some ballast for running some small off-grid loads. They sit there ready to keep us powered during grid outages. They are ex telco/data centre backup batteries so designed for precisely this purpose. 380Ah @ 48V.

You could just have them connected to a top up charger when you have excess solar PV, and let them rest otherwise.

If ever I can use more of my off-grid solar PV system's output then I'm still toying with the idea of having them in a parallel arrangement with some LiFePO4, about 100Ah/48V would do. The LiFePO4 can happily cycle away dealing with day to day PV supply and load demand balance, even discharging some each evening to keep the lead on float, while the lead is there for deeper discharge needs/backup.

 

[12VoltInstalls]

You could just have them connected to a top up charger when you have excess solar PV, and let them rest otherwise.

Good idea
With a 10A adjustable volt and amps charger (less than 2A @ 120V) and a <$20 high-low voltage controller relay rated at 10A high, you could just have them daisy-chained in a balanced pattern 2P3P with 10ga wire and have them automagically maintained…

 

[brum]

I saw an EPEVER solar charger controller with two battery outputs. It is targeted at RVs - charge the leisure and the starter battery. There was some prioritization on what and when to charge.

But the idea is that there may be more such controllers - they should be able to charge both batteries with different priorities.

The question of what you would do with them remains open to me. If I have sufficient capacity from the LiFePo4 I would keep the system as simple as possible. This will result in higher reliability.

Or you can just use DC to DC battery charger configured to float the lead-acid batteries. Keep them as backup and use them only in case of emergency.

I have a similar situation. Four LiFePo4 cells are on the way to me and they will be used to build a battery for camping purposes. It will replace the heavy lead-acid gel battery (still like new, <50 cycles at 20 to 50% DoD). But I will just sell the bulky lead-acid one.

 

[gelmjw]

Add the LFP in parallel with the AGMs.
That will solve problems with all the reasons LFP has to disconnect.

E.g., I have an SCC that shuts off and will not reconnect without a battery. When the LFP shut down due to Low Temps, the AGMs kept the SCC, and the loads, going for three days running; giving me more days of autonomy as well.

 

[welnat]

I am asking this same question, what is the best way to charge the AGM's without changing settings on charge controllers and inverter and switching banks constantly.

I was thinking only option was to decide between 120v charger and 120/240v charger. Leaning 120v so portable and can be used on other projects off site.

Now... if one were willing to compromise on the usable volume on the lithium iron phosphate battery, i.e. only charging to 56v (same as AGM setting) floating at 54v and by disabling equalization, would it be a stupendously bad idea to charge and discharge together?

Where your Lithium iron phosphate battery is 200Ah and the AGM is 800Ah (with a low voltage cut-off that leaves a usable 350Ah of the AGM.

 

[wattmatters]

only charging to 56v (same as AGM setting) floating at 54v and by disabling equalization, would it be a stupendously bad idea to charge and discharge together?

My AGM settings are bulk 56.4V and float at 54V.

56.4V / 16 LiFePO4 cells = charging to 3.525V/cell
54.0V / 16 LiFePO4 cells = floating at 3.375V/cell

I just don't see how that's really going to be much of a problem for the LiFePO4 or the AGMs.

 

[12VoltInstalls]

don't see how that's really going to be much

This has been educational.
But I think you’re right.

 

[Red Squirrel]

Get an inverter-charger and use them as a UPS for computer or other equipment. You can use them with a regular UPS but I find a lot of UPSes charge at too high of a voltage, which is why the gel cells never last in them. I have a 12v Tripp Lite I use with my servers with several 12v FLA batteries and it works great.