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

[markopolo]

Re: benefits - I'll add that a mixed lead acid & lithium system should lessen the average depth of discharge for the lead acid battery and likely result in a better chance of it getting fully recharged more often and therefore extend its life.

That's the theory .............

Michael is getting real data though & will likely let us know how it's working out.

[@Michael]

Originally Posted by hbn7hj

How is this going? Do we have a hybrid system grandma can run that we can get the power out of both batteries without intervention? Same with charging?

In may case, because I want to leave the chassis batteries/alternator as is, and be able to pull the Lithium in 0F weather, I think that it's going to be hard to have a 'fiddle-free' hybrid system unless I have a way of integrating a micro-controller or something else with a bit of programmable logic.

If I were to start over, I'd probably put two configurable B2B's back-to-back & come up with a means of making sure that only one was operating at a time. The SSR's that I have (Thornwave) close when the control pin is grounded, open on either 12V or when left floating. So what I'd need is a means of grounding either SSR (but not both). An SPDT would be fine. A micro-controller would be better (Arduino perhaps?).



The BIM-160 (OEM Coachmen) combines the batteries on either side based on voltage and time.

The charge sources and loads could be on either bank.

If I were confident in leaving the lithium in place in below 0F weather, I'd probably simplify the whole mess either by going pure lithium, or by putting all the charge sources on the lithium side and leave the load on the AGM side. In that case the input to the lithium B2B would be the chassis battery, and other sources (shore power, solar) would be on the lithium side. AGM's would always be charged using the AGM B2B, programmed with proper source-voltage cutoffs.

[hbn7hj]

“If I were to start over, I'd probably put two configurable B2B's back-to-back & come up with a means of making sure that only one was operating at a time.“

I have that. It is easy. Just put the outputs of both chargers on a double pole double throw switch.

Not sure exactly how I wired it. Think it was done with a single pole double throw switch. Will post when I figure it out. Works very well.

Needs to be a 50 amp DC switch.

Drive down the road and charge the lithium from the alternator through a B to B or charge the FLA from the lithium through a B to B.

Charge lithium from the generator through an AC lithium charger.

[hbn7hj]

FLA-alternator line to pole.
One throw to B to B input whose output goes to lithium.
2nd throw to B to B output whose input goes to lithium.

Only one B to B can be activated at a time.

[@Michael]

Originally Posted by hbn7hj

FLA-alternator line to pole.
One throw to B to B input whose output goes to lithium.
2nd throw to B to B output whose input goes to lithium.

Only one B to B can be activated at a time.

Yep - in my case it would look like:



As to whether the function of the AGM B2B can be met with a Schottky diode, the advantage would be cost. The disadvantage is that the diode doesn't provide a lead-acid charge profile.

[@Michael]

Originally Posted by markopolo

Re: benefits - I'll add that a mixed lead acid & lithium system should lessen the average depth of discharge for the lead acid battery and likely result in a better chance of it getting fully recharged more often and therefore extend its life.

That's the theory .............

Michael is getting real data though & will likely let us know how it's working out.

As far as the Schottky setup that I installed a few weeks ago, I got distracted for a week or so & left the camper on shore power, so I don't have interesting data since the stuff I posted earlier in the thread. It's back on battery now, so in a day or three I'll have more data.

I have a much shinier dashboard though. Shiny is important.

[markopolo]

That looks very cool Shiny is better!

[markopolo]

Michael - in this post you mentioned that the WFCO converter brings the batteries up to 13.6V - https://www.classbforum.com/forums/f...tml#post115236 -

Are you not getting a full 14.4V absorption stage to your AGM's?

Some thoughts / ideas:

Using a battery to charge a battery via a B2B device has got to be around a 5% loss (or worse) so would best be avoided except for emergencies (IMO).

The DIY idea I posted here - https://www.classbforum.com/forums/f...tml#post115584 - has the B2B from the lead acid battery to the lithium battery but only happening when there's power from the alternator, converter or solar. The system has to be above 13.6V for the B2B to charge the lithium battery.

Solar & the converter will (should) have lead acid profiles - let them handle it. If off-grid, use the alternator for bulk recovery so that solar has a chance to finish the charging. (or a generator if you have one)

The BIM in Michael's RV kind of seems like a problem to me. I have combiner device in my van that complicates the hybrid design also so that's why I left it out on the DIY idea mentioned earlier and just used an isolator.

If the BIM was replaced by an isolator (Victron Argo Fet maybe?) and an AMP-L-START - https://www.classbforum.com/forums/f...tml#post110679 - would that help to simplify things? Maybe even turn the AMP-L-START off when actually using the van and only have it on when not using the van.

[hbn7hj]

“Using a battery to charge a battery via a B2B device has got to be around a 5% loss (or worse) so would best be avoided except for emergencies (IMO).“

This is the center point of my installation. It is the only reasonable way to get an FLA to 100% when solar is not enough. Certainly more efficient than running a 2.8kw or 4kw generator for four hours. Works very well for the goal of both battery banks to 100% SOC by sunset, daily.

[markopolo]

The energy to get both batteries back to 100% has to ultimately come from somewhere other than one of the batteries else they couldn't both be at 100%.

With parallel lead acid / lithium setups (of the type I envision) some energy is going to be transferred from the lithium to the lead acid battery because they're in parallel so by definition that is charging even if micro trickle charging. Doing it as efficiently as possible should at least help reduce charging times.

I don't see purpose of using the lead acid battery to charge the lithium battery for example (as I think Michael has previously mentioned). Similarly, I think charging the lead acid battery over what is happening naturally via the parallel connection should be able to be avoided most of the time.

It seems like using a B2B to charge one battery from another battery particularly when no other charge sources are present is like moving your money between two accounts and every time you do it you pay a 5% or more fee. You'd soon stop doing it and have your direct deposits go where needed to avoid the fees.

[booster]

As I read all of this, I have to go back to what was the original premise for a hybrid system of lithium and AGm that was discussed some time ago.


The original idea was to cut a break for those that didn't have a lot of battery capacity, but did have a generator. The problem with having AGM in that circumstance is that you either have operate the AGMs in the middle of the SOC range so they will accept enough energy for use or take many hours of charging with the generator to get them full.


It started out as using a lithium battery about 1/3 the size of the AGMs and the entire setup would charge parallel until the AGM hit the SOC where it was not accepting as much energy. The lithium would be full by then. The generator would be shut off and the AGMs topped off over a long period from the lithium battery through a B to B charger. If it was desired to have the lithium full also, the generator could then be run for a very short time to refill the lithium.


By doing the topping charge of the AGMs off the lithium and then replacing that charge in the lithium the long topping off charge time for the AGMs from the generator would be eliminated.


The side benefit would be the lithium could be easily removable in cold weather use with just the AGMs.



I guess the idea of mixing other ratios and parallel use all the time doesn't seem to have as much benefit for all the trouble to me. Others obviously see more merit to it.


I could see having a small, backup only AGM in a lithium system like Roadtrek did only offline unless needed to preserve it, to be able to more easily recover the system and activate the charging sources.

[markopolo]

That is probably what Harry is doing and I understand it better from your longer explanation.

I see it being used a bit differently with the lead acid kept at a higher SOC because of the newly parallel lithium battery add-on. If the lead acid battery starts the day at a higher SOC then solar has a better chance to get it full.

Basically, it's use the lithium battery as much as possible. The lithium battery doesn't need to be fully charged daily.

Because I've never had a constant drain like a compressor fridge to deal with I always see it over days of use and not daily use. Like day 1 & 2 on the lithium battery and getting into the lead acid battery on day 3 and you're driving on day 4.

Clearly, there's no one solution for everyone. One idea that appeals to me is just to straight parallel (by bypassing the diode) a portable lithium pack once at camp.

[hbn7hj]

The energy to get both batteries back to 100% has to ultimately come from somewhere other than one of the batteries else they couldn't both be at 100%.

It comes from the generator

With parallel lead acid / lithium setups (of the type I envision) some energy is going to be transferred from the lithium to the lead acid battery because they're in parallel so by definition that is charging even if micro trickle charging. Doing it as efficiently as possible should at least help reduce charging times.

The lithiums are never paralleled with lead acid other than through momentary switching

I don't see purpose of using the lead acid battery to charge the lithium battery for example (as I think Michael has previously mentioned). Similarly, I think charging the lead acid battery over what is happening naturally via the parallel connection should be able to be avoided most of the time.

The purpose of retaining the lead acid battery is twofold. 1. The non temperature controlled battery compartment would otherwise not help electrically. 2. Interface with the standard alternator is retained.

The lead acid battery only charges the lithium through a B to B charger when the alternator is charging the lead acid. Really it is the alternator charging the lithium, not the lead acid battery. There is just no reason to unhook it.

It seems like using a B2B to charge one battery from another battery particularly when no other charge sources are present is like moving your money between two accounts and every time you do it you pay a 5% or more fee.

That is never the case. The generator charges the lithium more rapidly than it can charge the lead acid so let the lithium top off the lead acid over four hours, noise free. The generator recharges the lithium in 15 minutes.

You'd soon stop doing it and have your direct deposits go where needed to avoid the fees.

It works very well. The others are trying to remove manual intervention. I hope they do it.

[markopolo]

Originally Posted by hbn7hj

.................. The lithiums are never paralleled with with lead acid other than through momentary switching..............

That's a fundamental difference to how I see using it. I'm in favor of having them in parallel.

[booster]

I went back and found the original thread on it all and it was a lot longer than I remembered at 86 posts. There are several more recent threads as Harry worked out the bugs in his system that he built based on the first discussions. Hard to believe it was only a couple of years ago.


https://www.classbforum.com/forums/f...ymer-7383.html

[markopolo]

I also went back and read through the older posts this morning about combining lead acid and lithium batteries. I missed lots of interesting stuff while wintering in Florida. I didn't get interested until Nov 2018.

Looks like it started in Feb 2018 with GeorgeB posting about the LE300 Lithium add-on for AGM equipped coaches. Booster pursued the idea from there proposing DIY ideas & built a small test system and Harry was onboard early with a working system by March 2018.

First mention of using a diode was by Mfturner in Feb 2018 so my idea of using it is not new. Early on it was suggested that using up the lithium and preserving the AGM or FLA would be preferred so again, not a new idea.

An old post from Apr 2018 by Harry caught my attention. Note: I absolutely respect the work and ideas that Harry has done on this topic and just want us as a group to make the concept as easy to use, efficient and as low cost as possible.

Originally Posted by hbn7hj

Sunrise LA 83% Li 69%
8AM Generator start
8:30 Generator off LA 88% Li 100% DC to DC charger on. Solar on.
11:00 LA 100% Li 70% DC charger off.
3PM LA 100% Li 100%
.............................

My guess is that 70Ah appears to have been used overnight. The FLA batteries were down 38Ah but the LFP battery still had 69Ah capacity left.

IMO, the FLA shouldn't have been used at all that night as there more than enough energy in the LFP to provide what was needed. Approximately 41Ah would have been returned by the generator run. I don't know how much solar was involved but a 100W panel should average 30Ah per day into the system. It would be roughly 70Ah down and 70Ah+ returned without involving the FLA batteries at all and enough capacity to get through another night if the posted morning deficit is from typically use. Net energy use between 8:30am and 3:00pm appears to already be accounted for.

If I'm on the wrong track or simply not getting it or missing something etc. please tell me. As previously mentioned, I just want us to, as a group, make the concept as easy to use, efficient and as low cost as possible.

[booster]

Originally Posted by markopolo

I also went back and read through the older posts this morning about combining lead acid and lithium batteries. I missed lots of interesting stuff while wintering in Florida. I didn't get interested until Nov 2018.

Looks like it started in Feb 2018 with GeorgeB posting about the LE300 Lithium add-on for AGM equipped coaches. Booster pursued the idea from there proposing DIY ideas & built a small test system and Harry was onboard early with a working system by March 2018.

First mention of using a diode was by Mfturner in Feb 2018 so my idea of using it is not new. Early on it was suggested that using up the lithium and preserving the AGM or FLA would be preferred so again, not a new idea.

An old post from Apr 2018 by Harry caught my attention. Note: I absolutely respect the work and ideas that Harry has done on this topic and just want us as a group to make the concept as easy to use, efficient and as low cost as possible.



My guess is that 70Ah appears to have been used overnight. The FLA batteries were down 38Ah but the LFP battery still had 69Ah capacity left.

IMO, the FLA shouldn't have been used at all that night as there more than enough energy in the LFP to provide what was needed. Approximately 41Ah would have been returned by the generator run. I don't know how much solar was involved but a 100W panel should average 30Ah per day into the system. It would be roughly 70Ah down and 70Ah+ returned without involving the FLA batteries at all and enough capacity to get through another night if the posted morning deficit is from typically use. Net energy use between 8:30am and 3:00pm appears to already be accounted for.

If I'm on the wrong track or simply not getting it or missing something etc. please tell me. As previously mentioned, I just want us to, as a group, make the concept as easy to use, efficient and as low cost as possible.

There certainly was a lot of interesting stuff in the early discussions, some turned out good, some not so good, but that is the way of all development stuff.


The example quoted that Harry saw in his test was how I would envision the system working assuming a relatively small lithium battery compared to the AGMs. The assumption is also that the lithium would not be large enough to run on full time and just save the AGMs for special duty use. Of course this is all speculation as I do not have such a system, or really even intend to build one.


In essence, even with the small lithium, depending on how often you charge the lithium with generator or driving, you are running on the lithium battery through the B to B charger whenever it is on, even though the van is connected to just the AGMs.


The big deal would be to allow someone with a one or two AGM, or wet cell, setup to take good care of the batteries when off grid for longer periods, where generator running is needed to recharge the batteries. Running the generator 5-6 hours to top off to full on lead acid batteries, which is needed regularly, is prohibitive and the run time could be cut to probably by 80%. The cost would be quite low compared to a full lithium system which is often a huge factor.


I find it very interesting about the expanding into full or partial time true parallel systems and hope they work out well for what the users are trying to accomplish. Always interesting to watch evolution of ideas.

[hbn7hj]

Originally it was 100ah Li and 225ah FLA. FLA was used for evening TV and lights, Li was used for furnace or inverter for heated mattress pad. It took less power to run a heated bed than the furnace. I was at 9000 ft so the nights were in the 30’s.

Now that I have 400ah of Li the FLA gets used less and less ‘cause it is such a pain to charge the FLA. It usually stays above 90%. The main advantage now of the FLA is the no cost interface with the alternator.

It works very well as power is no longer a problem. Before I could choose between SAT TV or furnace with a big effort to bring the FLA up from 60% the following day with only 200 watts of solar. Now if I want the FLA at 100% I just flip a switch and wait a few hours. No noise.

We all put it together as a team, hopefully we can improve it.

No one has duplicated it that I know of.

[gerrym51]

on a boat

https://www.youtube.com/watch?v=R_RPQgS7R2s

[@Michael]

Got a days worth of data on the Victron Argo Battery Combiner (Schottky Diode) combined Lithium/AGM setup.

As before, the Lithium supplied majority of current untill lithium voltage dropped to approx 12.6, after which AGM supplied most of the current.

Setup:

• Schottky (Victron Argo Combiner) wired with lithium on one input, AGM on output.
• Batteries fully charged
• Constant 5-6A load on AGM
• Solar attached to lithium bank
• No load on lithium, other than Schottky
• Unplugged from shore & connected Schottky @4pm
• Ran from combined battery bank overnight

Power supplied by solar appears to go direct to load & is not seen by the monitors.

Analysis:

• Monday 4pm -Lithium discharged into AGM until AGM reached -.3V difference
• Mon 4-6pm - Solar supplied some current. As Solar tapered off, Lithium supplied most current
• Mon >6pm - Solar declined, Lithium supplied most current
• Tue 7am - banks supplied equal current
• Tue 7-10am - AGM supplied most current
• Solar charged lithium battery starting at 10am, with banks still combined via Schottky
• While charging during the day Tue, Lithium absorbed most of the charge

For reference, here's the current wiring diagram:



The Victron Combiner in the drawing is the Schottky diode device.