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

[hbn7hj]

As an observation there were many postings about hybrid electrical systems since 2018. Most of the posters just faded away. One or two built good systems that worked, shared them, and left. It is interesting that no two of us will build and use the identical system. We are still in development.

Eventually there will be no new coaches with lead acid systems. For now, a hybrid system is a very good way to upgrade an old coach with a lead acid system to a modern, high capacity, lithium system, that doesn’t need solar.

[markopolo]

Originally Posted by @Michael

Got a days worth of data .................

Thanks for the update Michael. To me, it appears that the results show that the interaction between the LFP and AGM is as anticipated. The difference between straight parallel and safer parallel via Schottky diode is that the AGM shares the load earlier with the Schottky diode in place and that's also predictable.

Solar ...

Some more thinking about how best to use solar with the dual chemistry setup would be good at this point.

The AGM's have the requirement to be fully recharged for longevity. The 0.3V increase to the AGM's if not going through the lithium battery should be beneficial. However, the solar harvest might be greater if the solar controller output goes to the lithium battery.....

Diodes ...

Another type of diode that's worth looking into is an Ideal Diode. There is no voltage drop with those. There is some current use though. I've considered using one for my project several times but the .3V difference with a Schottky diode permits using a voltage sensing relay to turn on or turn off DC to DC charge controller for example and that allows automation.

In another topic you mentioned the converter goes to 13.6V. Does it ever get to 14.4V? I can trick my PD converter into outputting 14.4V by a combination of power off then power on with no battery then power off again and then power on with battery (or some similar combo).

[booster]

Everyone has been in much detail on looking at this stuff compared to me, but I do have a bit of a question on the charge and discharge sequencing.


Since the AGM really doesn't do anything for carrying load until the voltage gets quite low, why not leave them disconnected from each other until the voltages are closer together and forget the diodes? Use a voltage triggered relay to connect and disconnect at maybe 12.9v?


If all the loads are on the lithium, as well as the charging, I think they would only be connected when discharging and below the relay trip point. If needed or wanted a second relay could control a B to B charger from the lithium to AGM if you wanted better charge control for the lithium, or wanted to charge the AGM from the lithium with no chargers running. That relay could be charger on controlled and/or with a manual override for no chargers charging of the AGM.

[@Michael]

Originally Posted by hbn7hj

As an observation there were many postings about hybrid electrical systems since 2018. Most of the posters just faded away. One or two built good systems that worked, shared them, and left. It is interesting that no two of us will build and use the identical system. We are still in development.

Eventually there will be no new coaches with lead acid systems. For now, a hybrid system is a very good way to upgrade an old coach with a lead acid system to a modern, high capacity, lithium system, that doesn’t need solar.

I agree with your observations.

I think that the various permutations of a hybrid will fit different use cases, depending on the relative capacity of the lithium vs. LA & the relative capacity of battery banks vs. utilization. Seems like (from your experience and that of others) if one has small lithium/large LA, then your original design of using the lithium to enable fast charge/short generator run times makes sense. OTOH if you have large lithium/small LA the use of the LA would be minimal and the design could be quite simple.

--Mike

[markopolo]

Originally Posted by booster

Everyone has been in much detail on looking at this stuff compared to me, but I do have a bit of a question on the charge and discharge sequencing.

Since the AGM really doesn't do anything for carrying load until the voltage gets quite low, why not leave them disconnected from each other until the voltages are closer together and forget the diodes? Use a voltage triggered relay to connect and disconnect at maybe 12.9v?

If all the loads are on the lithium, as well as the charging, I think they would only be connected when discharging and below the relay trip point. If needed or wanted a second relay could control a B to B charger from the lithium to AGM if you wanted better charge control for the lithium, or wanted to charge the AGM from the lithium with no chargers running. That relay could be charger on controlled and/or with a manual override for no chargers charging of the AGM.

General comments:

The diode provides isolation. I can hold an AGM at 14.4V and the LFP at 13.2V for example with the batteries connected together via the Schottky diode.

Loads on lithium would stop working if the lithium BMS disconnects due to low/high temperature, current, voltage. Also, some want to remove the lithium due to temperature or portable use etc.

[@Michael]

Originally Posted by markopolo

Some more thinking about how best to use solar with the dual chemistry setup would be good at this point.

The AGM's have the requirement to be fully recharged for longevity. The 0.3V increase to the AGM's if not going through the lithium battery should be beneficial. However, the solar harvest might be greater if the solar controller output goes to the lithium battery.....

In my setup I can switch the solar to either bank & reset the charge profile. But that's pretty fiddly. I think that leaving the solar on the lithium and using a DC-DC to charge the LA from the lithium would be better, as you'd always be assured of a proper charge profile for the LA's. The DC-DC could be small - 10A or so. Programmable would be best - you could set thresholds and mostly forget about it.

Originally Posted by markopolo

In another topic you mentioned the converter goes to 13.6V. Does it ever get to 14.4V? I can trick my PD converter into outputting 14.4V by a combination of power off then power on with no battery then power off again and then power on with battery (or some similar combo).

As best as I can figure & from reading forum posts, WFCO's rarely if ever get up to 14.4'ish. Seems like a certain combination of battery discharge, distance from converter to battery wire gauge & a bit of magic incantations are required.

In the last few months I've become a fan of integrated Bluetooth/networked/programmable technologies & particularly Victron stuff. Then I have a chance of making it do what I want.

[booster]

Originally Posted by markopolo

General comments:

The diode provides isolation. I can hold an AGM at 14.4V and the LFP at 13.2V for example with the batteries connected together via the Schottky diode.

Loads on lithium would stop working if the lithium BMS disconnects due to low/high temperature, current, voltage. Also, some want to remove the lithium due to temperature or portable use etc.

If the connection only happened at a set point like below 126v, why wouldn't you also be able to hold 14.4 and 13.2v or even charge either independently?


The loads would connect between the lithium and it's BMS and the voltage disconnect relay. If the lithium disconnected or was removed, the relay would just be connecting to the loads only and not the lithium at the same time.

[GallenH]

So here's an odd question. Suppose your AGM fully supported your cabin needs and you wanted to add a compressor fridge. Could you:

Add 200AH of lithium. That lithium would be the recipient of all existing charging sources: alternator, solar and shore power. It's primary responsibility would be to run the compressor fridge and it would be directly wired there.

It's secondary responsibility would be to charge the AGM via a B2B charger that would be perhaps triggered by the AGM's voltage falling to a certain point and then disconnected when the AGM reached a desired voltage/state of charge.

Possible? Or deeply flawed?

[peteco]

Originally Posted by GallenH

So here's an odd question. Suppose your AGM fully supported your cabin needs and you wanted to add a compressor fridge. Could you:

Add 200AH of lithium. That lithium would be the recipient of all existing charging sources: alternator, solar and shore power. It's primary responsibility would be to run the compressor fridge and it would be directly wired there.

It's secondary responsibility would be to charge the AGM via a B2B charger that would be perhaps triggered by the AGM's voltage falling to a certain point and then disconnected when the AGM reached a desired voltage/state of charge.

Possible? Or deeply flawed?

I am contemplating the same thing.

[@Michael]

Originally Posted by GallenH

So here's an odd question. Suppose your AGM fully supported your cabin needs and you wanted to add a compressor fridge. Could you:

Add 200AH of lithium. That lithium would be the recipient of all existing charging sources: alternator, solar and shore power. It's primary responsibility would be to run the compressor fridge and it would be directly wired there.

It's secondary responsibility would be to charge the AGM via a B2B charger that would be perhaps triggered by the AGM's voltage falling to a certain point and then disconnected when the AGM reached a desired voltage/state of charge.

Possible? Or deeply flawed?

Certainly possible. Or put the fridge on an A/B SPDT switch and switch banks as needed.

Edit: You'd have to figure out how to ensure that your alternator is compatible with your lithium battery. That's a potential problem area.

[markopolo]

Originally Posted by booster

.................... Since the AGM really doesn't do anything for carrying load until the voltage gets quite low, why not leave them disconnected from each other until the voltages are closer together and forget the diodes? Use a voltage triggered relay to connect and disconnect at maybe 12.9v?

If all the loads are on the lithium, as well as the charging, I think they would only be connected when discharging and below the relay trip point. If needed or wanted a second relay could control a B to B charger from the lithium to AGM if you wanted better charge control for the lithium, or wanted to charge the AGM from the lithium with no chargers running. That relay could be charger on controlled and/or with a manual override for no chargers charging of the AGM.

Originally Posted by markopolo

General comments:

The diode provides isolation. I can hold an AGM at 14.4V and the LFP at 13.2V for example with the batteries connected together via the Schottky diode.

Loads on lithium would stop working if the lithium BMS disconnects due to low/high temperature, current, voltage. Also, some want to remove the lithium due to temperature or portable use etc.

Originally Posted by booster

If the connection only happened at a set point like below 126v, why wouldn't you also be able to hold 14.4 and 13.2v or even charge either independently?

The loads would connect between the lithium and it's BMS and the voltage disconnect relay. If the lithium disconnected or was removed, the relay would just be connecting to the loads only and not the lithium at the same time.

With the diode in place and no charging sources present, the lithium into the AGM connection is charging but it lacks the force of higher voltage. You're "charging" a high SOC AGM at maybe 13.1V at most because of the diode. Kind of like a trickle charge.

The lower voltage connect set point idea is interesting. Automatic connect / disconnect requires two set points. So you'd disconnect at a "high" voltage and connect at a "low" voltage. That's the opposite of ACR's. It probably worth finding the parts needed and figuring out the total current draw if it consists of multiple relays. There's not much energy in LFP at 12.6V OCV though so maybe no reason to connect then.

Typically, you don't want a direct path from the alternator to the lithium battery. In/out are the same wires with your van's AGMs. When you add a DC-DC controller for the lithium "in" then you have different wires for the "out". You'd have to certain the relay setup can't ever let that direct connection happen on the "out" (the load) side when the engine is running. The diode prevents charging to lithium battery on the load wires.

Nothing should be between the BMS and the lithium cells. The risk is an unrecoverable pack due to discharging below 10V or some voltage like that.

[booster]

Originally Posted by markopolo

With the diode in place and no charging sources present, the lithium into the AGM connection is charging but it lacks the force of higher voltage. You're "charging" a high SOC AGM at maybe 13.1V at most because of the diode. Kind of like a trickle charge.

The lower voltage connect set point idea is interesting. Automatic connect / disconnect requires two set points. So you'd disconnect at a "high" voltage and connect at a "low" voltage. That's the opposite of ACR's. It probably worth finding the parts needed and figuring out the total current draw if it consists of multiple relays. There's not much energy in LFP at 12.6V OCV though so maybe no reason to connect then.

Typically, you don't want a direct path from the alternator to the lithium battery. In/out are the same wires with your van's AGMs. When you add a DC-DC controller for the lithium "in" then you have different wires for the "out". You'd have to certain the relay setup can't ever let that direct connection happen on the "out" (the load) side when the engine is running. The diode prevents charging to lithium battery on the load wires.

Nothing should be between the BMS and the lithium cells. The risk is an unrecoverable pack due to discharging below 10V or some voltage like that.

I think a Victron monitor could do it off voltage or SOC of the lithium. The contact arrangement is SPDT if it remember correctly from the literature. It would be interesting to see if any of the low battery cutouts have double throw relays in them so they would work opposite.


Yep on the BMS and other stuff location, that is why the loads would have to go after the lithium and it's BMS, but before the connect/disconnect relay.

[@Michael]

I got a few weeks of camping using the hybrid design outlined in this post and diagrammed here:



Summary:

• I never found a reason to combine the lithium and AGM's using the 80 amp Victron battery combiner. It's now for sale.
• By design, the chassis/coach OEM Precision Circuits battery interface does not combine the chassis and coach batteries unless one or the other is discharged and the other is charging. Because of this I hit a corner case where if the AGM coach batteries were charged, the Precision Circuits interface would stay disconnected and I couldn't use the alternator to charge the Lithium via the Redarc B2B. The solution was to make sure the AGM's were partially discharged before traveling.
• The Ford alternator doesn't fully charge the AGM's. I assume this is partially because of how the Precision Circuits battery interface works, and partially because the alternator doesn't really have a suitable charge profile.
• The WFCO converter has no temperature compensation, so I was unlikely to get a fully charged AGM battery under most circumstances.
• My WFCO converter failed on the first night of the 3-week trip, so I no reliable means of keep the AGM's charged for the remainder of the trip.

Since I had to buy a new converter anyway, I decided to re-design (again!), this time shifting towards relying on the alternator more and shore power less. This should fit our travel style, as we move pretty often - even if only from the campground to the trailhead.

A major constraint is that I still feel that I need to be able to disconnect and/or remove the lithium battery in the case that we have sustained temps substantially below 0F, at least until I get good data on the effectiveness of my battery heater.

New to the implementation is an inexpensive Victron Blue SmartIP-22 30A shore charger, a Victron Orion 18A B2B, and a Victron Smart BatteryProtect low voltage disconnect.

I set it up so that the alternator charges the lithium battery via the solid state relay (SSR) & Redarc DC-DC charger, and the AGM’s via the B2B A/B switch and Victron DC-DC charger. The Transit alternator has adequate capacity to charge both simultaneously.

The Victron DC-DC can also use the lithium battery as a charge source via the B2B A/B switch, so I could in theory use the lithium to charge the AGM's. That might be useful if I have the solar panels out and need to top off both the lithium and AGM coach batteries, though I'm not sure I'll ever do that.

The solar can charge either lithium or AGM depending on position of solar A/B switch.

The Victron IP-22 charger/converter charges whichever bank is currently supplying the camper load, selectable via the load A/B switch.



For the shore and solar chargers, I use the Bluetooth app to switch charge profiles whenever I flip the A/B switches, otherwise I end up with temperature compensation on the lithium battery.

The Victron Orion DC-DC has no temperature compensation, so if I am relying on it alone I have to set up charge profiles that have higher or lower voltages. I'll create a handful of profiles to cover different temperature ranges. Switching is easy via the Bluetooth app.

I lost the ability to automatically top off the chassis battery via the Precision Circuits battery interface. I use the campervan enough that I don't think that matters. If it does, I'll use an AMP-L start or equivalent.

This is the final revision...untill the next one.

--Mike

[markopolo]

Looks like there's the option for a lithium battery to chassis battery in parallel if ever needing to get an emergency boost. If switches are left in the wrong positions is there a risk of a direct alternator to lithium path?

Interesting new equipment. I'll have to explore the links.

[@Michael]

Originally Posted by markopolo

Looks like there's the option for a lithium battery to chassis battery in parallel if ever needing to get an emergency boost.

Yep. The load A/B is a 300amp A/B/Both, so I can tie them together directly. I did that a few times with the last design, just to see how much current the AGM's would absorb.

Originally Posted by markopolo

If switches are left in the wrong positions is there a risk of a direct alternator to lithium path?

Not as far as I can see. The A/B's that front-end the Victron B2B and Solar are SPDT break-before-make switches. The common sides of the SPDT's are the Victron B2B input and Solar charger output, respectively.

--Mike

[hbn7hj]

Looks like a switch free hybrid system is not a reasonable expectation.

The one switch system works very well. With 400AH of lithium the lead acid batteries are used less and less. They are there to interface with the alternator while driving.

I used them for power when the lithium bank was 200AH

[markopolo]

Harry - it appears that a no manual switch between AGM and Lithium system (ignoring the contactor) has been in production and right under our noses for maybe 5 years - http://home.roadtreking.ca/Manuals/F...cotrekVans.pdf

The AGM in that diagram is in parallel with the lithium battery on the charge side. At some point during discharge there will be load sharing between the AGM & lithium so you could also say it's on the discharge side also.

No diodes, no choosing when to use the AGM or lithium etc.

[hbn7hj]

Won’t the charge relays open up before you get much out of the AGM?
Maybe they wouldn’t open up on low Li voltage.

That AGM charge line is open with engine off is it not?

Somewhere I remember someone modifying those modules to get rid of the 6 amp parasitic draw making them much better.

[markopolo]

From Cruising's testing, the joined Lithium battery and AGM battery can be pulled down to 11.95V.
Charge side relays would probably be set more to control over-voltage rather than under-voltage.
Charge side relay would open and close based on voltage trigger settings and operator choosing to use a particular 200Ah module.
Parasitic losses caused by the 5 or 6 relays can be reduced by optimizing the voltage trigger points and having the least amount of relays using power at any time.


One of the ecotrek topics would be the better place for discussing them.

[@Michael]

Originally Posted by hbn7hj

Looks like a switch free hybrid system is not a reasonable expectation.

The one switch system works very well. With 400AH of lithium the lead acid batteries are used less and less. They are there to interface with the alternator while driving.

I used them for power when the lithium bank was 200AH

Resurrecting and old thread. The discussions on the DVB01 got me thinking about how to automatically transfer house load between battery banks. In my case, AGM and Lithium.

Seems like the DVB01 could be used to trigger a pair of solid state relays, one triggered by the Normally Open terminal, and one by the Normally Closed terminal. When the DVB01 sees low voltage on one bank, it changes the state of its relay, which would close one SSR and open the other, transferring load to the other battery bank.

Either the No or NC terminal on the DVB will always be conducting, so one bank or the other will always be active, and never both. My SSR's are triggered 'ON' by grounding the control terminal, so the DVB01 relay would ground either or the SSR's as appropriate.

The effect of a transfer would be fast, but not instant, so there likely would be a disruption in the house voltage. The SSRs are unidirectional, so would be subject to going up in smoke if there is any reverse current. Back-to-back SSR's would allow bidirectional current.

One could add an SPDT switch in parallel with the relay to permit manual changeover.

Maybe I'm missing something?

See attached.