Parallel lead acid and lithium circa 2018

[hbn7hj]

Keep the possibility of fire in mind. With the main charging done while driving you may not be able to monitor high charge rates from the driver's seat. Just a thought.

[kite_rider]

That thought has been on my mind as well! Especially since I'm planning to locate the batteries inside the living area right under the seat bench which is also the bed.

However, I've got ideas for this. 1. The battery will be fused, probably at 100A, but maybe 150A. 2. The battery cells will be BMS protected. The BMS board will disconnect the battery in several situations: under voltage situation, over voltage situation, and over current situation. 3. The battery monitor that I'm considering using (https://www.thornwave.com/products-btdcpm/) has relay control logic. So it will manage a 200A relay connection to the battery and automatically disconnect the battery when certain preset conditions are met. For example, I plan to disconnect the battery when it reaches 90% SOC (for longevity reasons); so this is the third way the battery should be disconnected before things get out of hand..

[booster]

Originally Posted by kite_rider

That thought has been on my mind as well! Especially since I'm planning to locate the batteries inside the living area right under the seat bench which is also the bed.

However, I've got ideas for this. 1. The battery will be fused, probably at 100A, but maybe 150A. 2. The battery cells will be BMS protected. The BMS board will disconnect the battery in several situations: under voltage situation, over voltage situation, and over current situation. 3. The battery monitor that I'm considering using (https://www.thornwave.com/products-btdcpm/) has relay control logic. So it will manage a 200A relay connection to the battery and automatically disconnect the battery when certain preset conditions are met. For example, I plan to disconnect the battery when it reaches 90% SOC (for longevity reasons); so this is the third way the battery should be disconnected before things get out of hand..

You are smart to be concerned about the possibility of over ampping things from the engine charging. IMO, this is one of the biggest, and most common, issues with many of the engine generator systems for both lithium and AGM. We went through this very issue with our upgrade to 440ah of AGM and very large alternator capacity.



I do not, however, think that dealing with the issue by disconnecting with fuses or overcurrent devices is a good way to do it, for several reasons.


The first issue is obvious. If you have low batteries that pull you into over current shut off, it will happen every time the batteries come back online and you will never charge your battieries.


Second would be that over current devices are normally not intended for cycling use to control anything, just to protect things. You would be doing a break cycle at full load, repeatedly, which is very hard on contacts and equipment. This rapid dropping of load would also give a possibility of a voltage spike out of the alternator.


Full shutoff of the batteries could leave the coach without power and the alternator without reference voltage, both of which are highly undesirable. Maintaining battery voltage reference is one of the hardest things to do in full shutoff charging systems.


The solution that we chose, which unfortunately is no longer available, was to use an Ample Power external regulator for the alternator that allowed us to set, and manually control from the dash, the current from the alternator charging at two fixed rates (actually sets field current max, so not truly setting output amps, but close enough). It works very well, in conjuction with an ammeter and two switches on the dash that I can see while driving. Very little input or watching needed.


A similar setup that could be done, and I think there may be some done this way, would be to use a Balmar external regulator and a properly selected size alternator. The alternators can only run at about 65-70% of rated continuously maximum, so you take that into account. The thermal trundown to 50% that is built in to the Balmar can be switch controlled, so you can get the 50% when wanted. You can also set another mode for switch control that allows setting for anywhere from 50-100% output, so you would be able to set that for the 65% maximum output you could get without overheating the alternator. The critical thing is getting the alternator size correct so you get your max amps you want without too much or too little. This is the setup we will likely use if our Ample Power regulator dies.


Another way to do it would be to get DC to DC charger into the wiring to the coach. It would limit current and you could shut if off when it was done charging. You would still need to make sure you maintain some sort of battery reference to the alternator unless you make sure to shut if off first, and turn it on last.

[Bud]

'Parallel lead acid and lithium' An example?:

https://inergytek.com/products/kodiak

Bud

[booster]

From the manual for Inergytek


NEVER connect an external battery that is morethan 0.1 volts different than the Kodiak at the time they areconnected. To illustrate, if your Kodiak is charged to 12.3 Volts at the time you wish to connect an external battery,
any external battery must measure between 12.2 - 12.4
Volts before they are connected. A simple Voltage meter
commonly available at local department stores can be used to measure your external batteries


This would seem to be addressing the excessive current from a full lithium battery to a discharger AGM, and is a mighty restrictive rule, IMO.

[Bud]

Originally Posted by booster

From the manual for Inergytek


NEVER connect an external battery that is morethan 0.1 volts different than the Kodiak at the time they areconnected. To illustrate, if your Kodiak is charged to 12.3 Volts at the time you wish to connect an external battery,
any external battery must measure between 12.2 - 12.4
Volts before they are connected. A simple Voltage meter
commonly available at local department stores can be used to measure your external batteries


This would seem to be addressing the excessive current from a full lithium battery to a discharger AGM, and is a mighty restrictive rule, IMO.

Yes, and after connected sucessfully?

[booster]

Originally Posted by Bud

Yes, and after connected sucessfully?

That is a good question and would go back to the comments made earlier in relation to charger size and voltage vs the relative size and and acceptance rates of the batteries.



At this point, we really don't know how big the operating window would be in use.


My guess would be what the are doing is using a charge voltage that will give nearly full full lithium batteries, like 13.6v, but would somewhat limit what the AGM batteries would accept, so that the different batteries would stay close to the same voltage. Of course, they may also turn off the charging to the lithium until the AGMs reach a certain voltage within the lithium battery range.


I think all of this is still in the infancy, but there will be quite a few different products coming out with variations of the idea now that Hymer has put it in th spotlight a bit. I am sure some will be done well, and some not so well, but we will find out that over time.



I think, for me, is that I don't see any way that they will ever get the AGM batteries full unless they have a full voltage shore charger running for a long time, otherwise they would need the 12v to 12v charger to get enough voltage to top off the AGMs as the lithium won't be at high enough voltage.

[Hondo]

I have 2 lead acid batteries currently installed in the 210 and would like to go to lithium in the future. Weight savings will be huge from what I have read.



The Tripp Lite inverter/charger manual states that they are are for wet or gel batteries and with the alternator issues I'll be following this closely.

[hbn7hj]

We will get the hybrid system RV back next week and will run a test or two.

The plan is to get both batteries to 100%, move the switch to both, set up about a 10 amp draw with solar off and record voltages, currents, and %charges every 10 minutes and see what happens. Open to any other suggestions.

Will charge it on both with the lithium charger with the same data keeping.

[hbn7hj]

Well, I checked it out. I never could get the lead acid battery to discharge, even with a 40% state of charge on the lithium the lead acid was still charging at 230 milliamps. With both batteries at 100% state of charge the lead acid was charging between 400 and 500 milliamps.

This is as expected. That means you are going to have a constant ~500 milliamp drain from the lithium when they are connected. Not good.

I found no problem leaving the batteries hooked together. Bottom line is you have to kill the lithium to use the lead acid. I did find out that 120 amp hours of battery runs a satellite TV a long, long time. You should put in two battery monitors anyhow, may as well put in the switch.

I didn't check charging but it would appear that the lithium would charge first.
Harry

[markopolo]

The system voltage would have to get to 12.8V or less for the AGM batteries to participate in supporting the load. I added a yellow line to this Trojan chart to show this:


Trillium chart.JPG

Note that it would all be proportional to battery capacity. That's a chart for the 110Ah battery.

In this example, if you are running a pump or a fan it will be lithium only. If you run the air conditioner or microwave oven then the AGM's would get involved in supporting the load.

[@Michael]

Originally Posted by markopolo

The system voltage would have to get to 12.8V or less for the AGM batteries to participate in supporting the load. I added a yellow line to this Trojan chart to show this:

[…]

In this example, if you are running a pump or a fan it will be lithium only. If you run the air conditioner or microwave oven then the AGM's would get involved in supporting the load.

Making sure I understanding this...

Because the lithium battery will stay above 12.8 under light loads or until it's nearly discharged, the AGM will not contribute to supporting the load unless either discharge rate is high, or lithium is nearly discharged?

[SteveJ]

Originally Posted by @Michael

Making sure I understanding this...

Because the lithium battery will stay above 12.8 under light loads or until it's nearly discharged, the AGM will not contribute to supporting the load unless either discharge rate is high, or lithium is nearly discharged?

Would this not be a good thing seeing how the lithium seems to be more charging friendly?

[hbn7hj]

Originally Posted by SteveJ

Would this not be a good thing seeing how the lithium seems to be more charging friendly?

It would if you didn't mind flattening the lithium. I do. All you have to do is put an A-B-Both marine battery switch in.

This doesn't explain how Hymer does it. Maybe they do it this way as it would work, I suppose. I just don't see killing the lithium to get to the AGM battery.

I object to the .5 amp constant drain, too.

[booster]

I think a lot of this discussion of which first came from Hymer's descriptions that said the AGM would always charge to full first, which most of us don't really understand why that would happen based on charging voltages and acceptance rates.

[markopolo]

I like the idea of using an A-B-Both marine battery switch also.

We need some data on in-rush/out-rush current flow between the two chemistries at various and differing states of charge.

[booster]

Originally Posted by markopolo

I like the idea of using an A-B-Both marine battery switch also.

We need some data on in-rush/out-rush current flow between the two chemistries at various and differing states of charge.

I agree on the inrush information, as that is a major determiner of if current limiting is needed in any particular system. There are currently very few ways available to current limit effectively, so that determination is very important.


When I did the very early test of a small lithium and small agm, using low cost ebay batteries, I found out a little. With the AGM at, IIRC. 20% SOC, and a full lithium, just connecting them together gave an inrush current large enough to destroy the cheap lithium BMS instantly.


The other thing that goes right along with the inrush current is what voltage would be chosen for the charging and what profile. There are some real problems, I think, in most of the options because what will take good care of the AGM will be bad for the lithium (14.3v for many hours), and a lower 13.8v would be good for lithium (maybe even as a float) but bad for the AGM.


It may not be really the best to just tie the two types together on one charger, which is what we had initially speculated, and Harry addressed in his system. But, things get more complicated, requiring manual inputs or automatic controls, rather quickly once you start adding 12v to 12v chargers and multiple shore chargers.

[avanti]

Another reason one might want individual charging is that one could charge the AGM under conditions too cold for Lithium charging. One could get started with AGM power while the heating pads are warming the Li.

[hbn7hj]

We have switched through the "Both" setting many times with the greatest SOC discrepancy being 57% LA, 100% Li with no problems but we didn't linger. We are using flooded lead acid batteries which probably react a bit differently than AGM batteries.

The question was can we tie the two battery types together permanently for a trouble free viable system. To me the answer is no. Total discharge of lithium is not acceptable nor is the .5 amp constant drain from lithium to lead acid.

My Roadtrek Chevy 190P system is about to go live. It will be a bit different with no dedicated lead acid charger but will use the DC to DC charger with or without the lithium charger on.
Harry

[SteveJ]

Originally Posted by hbn7hj

It would if you didn't mind flattening the lithium. I do. All you have to do is put an A-B-Both marine battery switch in.

This doesn't explain how Hymer does it. Maybe they do it this way as it would work, I suppose. I just don't see killing the lithium to get to the AGM battery.

I object to the .5 amp constant drain, too.

Thanks. I know just enough to be dangerous.

Skol!