Mixing lithium with AGM's - bashing around some ideas.

[hbn7hj]

Certainly has possibilities. The manual switch has make before break. I don’t have any way to charge lithium from the alternator. Adding a DC to DC charger would allow that.

Figuring out a way to make before break is the only thing left.

[markopolo]

The voltage hand-off / sharing from LFP to AGM is ideal.

possible blended LFP AGM SOC chart.jpg

I put 3 50A Ideal Diodes in parallel and it worked as expected. Minimal (almost unnoticeable) voltage drop, no heat, zero reverse flow etc. It was limited low-ish amp testing though & I plan to test more rigorously at some point.

It avoids the make-before-break issue. Minimal wasted current also.

It's probably constructed the least best way as using opposite ends would probably be best followed by using the middle for connection points but I used the piece of copper bar that I had on hand and don't plan to go anywhere near 150A current through it.

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Anyway, it's just another idea for mixing PbA & LFP. Every situation is unique so there will be many ways to do what's needed.

[@Michael]

Originally Posted by markopolo

I put 3 50A Ideal Diodes in parallel and it worked as expected. Minimal (almost unnoticeable) voltage drop, no heat, zero reverse flow etc. It was limited low-ish amp testing though & I plan to test more rigorously at some point.

How are these wired?

[markopolo]

There's an In terminal and an Out terminal. LFP Positive in & positive out to the PbA. The small wire is ground. There's a photo here: https://www.classbforum.com/forums/f...tml#post117595

I haven't found any documentation so I don't know what would happen if I broke ground for example. Maybe they'd burn out with high reverse current from the alternator... I don't know. I should test a small 15A Ideal Diode I have to see what happens.

Since then, I've seen much higher rated current Ideal Diodes on AliExpress. That's probably better than paralleling smaller Ideal Diodes. I haven't tested how much capacity would be lost from the LFP to the AGM through the Ideal Diode. A previous straight parallel test (no diodes) - https://www.classbforum.com/forums/f...tml#post109988 - indicated the capacity loss wouldn't be an issue for the way I'd use it. (easily, quickly recoverable)

My interest is still multi-use LFP. It's in the house most of the time for backup power if needed & put it in the van when needed so that's the type of projects I think about/work on.

[@Michael]

Originally Posted by markopolo

The voltage hand-off / sharing from LFP to AGM is ideal.

With that volage handoff, and if I wanted to favor the LiFePo4's and only use the AGM's as a backup, it seems like I could do something like this:



The load current would be supplied by the LiFePo4 until its voltage drops enough that the AGM starts supplying current, somewhere around 12.8 volts.

Solar and converter would have to be appropriately placed.

I might want a low voltage cutoff on the LiFePo4, if it's not already built in.

[@Michael]

Updates on my lithium<->AGM battery implementation.

After another year running with this hybrid design that allows me to switch between 210Ah OEM AGM battery and my 100Ah Battleborn lithium, I decided to give up on my requirement that I be able to run the camper with the lithium removed from the camper in case of severe cold.

That let me configure the camper as 'lithium only', eliminate the manual changeover between AGM and lithium, and relegate the AGM's to the role of starter batteries for the Onan generator. If I get rid of the generator, the AGM's will go too.

I also decided to abandon my Battleborn battery and switch to a 300Ah battery from a small startup in Baton Rouge, SFK (SunFunKits). They sell kits using mostly standard DIY components, with or without cells. Warranty is 5x as long as they've been in business, so should be good.

It fits in my only available space with about 1/8" clearance, has 3x the capacity of the BB, and a fairly capable BMS.



I had to move/rewire quite a bit to clear up that space.

Still making changes to my touchscreen camper monitor. The main screen is too cluttered. I'm trying to rely on Bluetooth Low Energy to communicate between the Raspberry Pi and the various microcontrollers. Programming BLE on a Pi is a pain. Seems like the Bluetooth stack on the Pi is buggy.

[markopolo]

SF Kits use special order BMS boards from Jiabaida (JBD) AFAIK. Some SFK boards might be basically stock JBD but others allow series connections for example. The JBD/Xiaoxiang & other apps I use would work with SF Kits BMS but the SF Kit app doesn't work with the Jiabaida labeled boards. I'd assume JBD's Windows software (JBD Tools) for calibrating voltage and current etc. would work with SF Kits boards. The BMS quality should be at least comparable to standard production JBD boards. The boards probably also allow users to enter custom settings such as voltage cutoff points or change the low temperature cutoff if desired for example as you can with stock JBD boards.

[@Michael]

Originally Posted by markopolo

SF Kits use special order BMS boards from Jiabaida (JBD) AFAIK. Some SFK boards might be basically stock JBD but others allow series connections for example.

My understanding is that the 200A SFK BMS that came with the battery is sourced from LLT Power, and apparently can be put in series up to 48v. The Xiaoxiang app works on the SFK BMS. I'm still using the SFK app, leaving the BMS settings alone & assuming that SFK set it up correctly. The SFK app is pretty clunky though - no reason to use it if the Xiaoxiang app works.

LLT Power is somehow related to JBD - perhaps as an OEM? Maybe the same company?

[RT-NY]

Originally Posted by @Michael

SFK (SunFunKits). They sell kits using mostly standard DIY components, with or without cells.

From the specs, these batteries look to be just a bit bigger than battleborn and similar 100AH batteries, but three times the capacity! What is the difference?

[markopolo]

Originally Posted by @Michael

My understanding is that the 200A SFK BMS that came with the battery is sourced from LLT Power, and apparently can be put in series up to 48v. The Xiaoxiang app works on the SFK BMS. I'm still using the SFK app, leaving the BMS settings alone & assuming that SFK set it up correctly. The SFK app is pretty clunky though - no reason to use it if the Xiaoxiang app works.

LLT Power is somehow related to JBD - perhaps as an OEM? Maybe the same company?

My assumption is that Jiabaida is the manufacturer of these BMS boards. I don't know for certain though. LLT appeared to be a convenient English language source of the boards when I was figuring stuff out a few years ago. The most current App and most current windows software was always found on Jiabaida's Chinese language site when I went searching for them.

[@Michael]

Originally Posted by RT-NY

From the specs, these batteries look to be just a bit bigger than battleborn and similar 100AH batteries, but three times the capacity! What is the difference?

I'm assuming that the primary difference is the rectangular shape of the prismatic cells in the SFK rather than the less space-efficient small cylindrical cells in the Battleborn. Not sure though.

I ran it down 300Ah from full and it was still at 12.6 volts, so the capacity is at least 300Ah.

[BillsPaseo]

Michael, you may find that just upgrading to better AGM batteries gets you to where you need to be. We upgraded to 2 Lifeline 125AH AGMs, and 380W of solar.

We just got home from 6 nights boondocking in eastern WA in the middle of a heat wave. Daytime temps around 101-107 degrees, nighttime temps 65-71 degrees.

Due to the heat, we ran the generator for about an hour each evening so we could run the AC to cool the van down to a decent sleeping temp. During the daytime hours, the Maxxair fan was left on high and the van side and rear doors open.

First morning, we were at 12.5 volts at 6AM, by the 5th morning we were down to 12.1, and that is the first time we got below the Novakool cutoff. To help recover, and because it was the hottest day at 107, we ran the generator about 3 hours that day, and the next morning we were at 12.4 volts. Then we drove home with the van AC on high... across the mountains and back to cooler weather.



Throughout the entire time, the fridge thermometer we keep inside it showed a steady 39 degrees.

Also, we ran the fan all night every night, and also the stereo system playing a white noise track (waterfall sounds).

[@Michael]

Originally Posted by BillsPaseo

Michael, you may find that just upgrading to better AGM batteries gets you to where you need to be. We upgraded to 2 Lifeline 125AH AGMs, and 380W of solar.

If you were in the sun, I suspect that your solar was able to recover the AGM's a fair amount during the day.

In retrospect, had I initially focused on getting rid of the WFCO converter (which was never able to run a proper absorption cycle) and on the low-voltage disconnect (which was fixed at 12.2v), I could have gotten by with the two 105Ah AGM's & no lithium - for a while anyway.

[BillsPaseo]

I should have read the entire thread before posting... didn't realize it was a 3 year old thread and that my reply was inapplicable...