Parallel lead acid and lithium circa 2018

[kite_rider]

My Lithium cells arrived after Thanksgiving and in between a few ski trips I was able to put my battery together and have been doing a number of tests.

Several notes and observations:

1. It turns out that the cells I have expand when changing (so I'm told) so they should either be banded together or put in some sort of case that compresses them slightly. Since I'm putting this in a very tight space inside my rig I ended up making a case out of marine grade 5/8" plywood and a combination of threaded rod with fender washers and lock nuts. My battery configuration is 4 Serial, 3 Parallel (4S3P) so I had to make some bus bars for the parallel part of the battery. I used 1"x1/4" aluminum metal bar for this. Seems to work OK. For monitoring and control I'm using a Thornwave PowerMon Bluetooth monitor connected to a 200A external shunt, 135A circuit breaker, and 200A automotive relay. The PowerMon controls the relay when the voltage goes too high or too low. I've also got a device that monitors the cells so I can see if they are in balance or not. I might buy a balancer if I determine that I need one later.

2. Though I had planned to run a hybrid system (as this thread implies), I had the house battery out for testing and replacement with the RV dealer. Turns out that my existing house battery was shot, delivering only a bit over 18Ah of energy (at a 5A drain rate, room temp)! Kudos to Carado and Blue Dog RV for standing behind the warranty on the original AGM house battery. Anyway, I did a bunch of testing with just the Lithium battery while the other battery was out.

3. I set up the on-board inverter / charger for a relatively light charge cycle. Max charge voltage of 14.4V then float at 13.8V with a bulk charge current of about 28A. This seems to work fine, but I've only been charging the battery up to about 60%-80%. Along the way I've been able to test the PowerMon's High Voltage / Low Voltage cut off so I've got some comfort that the battery will not be over or under charged. PowerMon has also corroborated the charge current so it seems to be working.

4. Though I've not been driving it, I was curious about the current the alternator provides. I've noticed peak currents of around 70 Amps after brief starts and idling for about 3 minutes. My rig is the Promaster with a 220A alternator. I also looked at the voltages (at the battery) when charged at around 80% and at idle and recall it being 14.4V.

5. Early testing seems to indicate that I'll have more than enough power for winter camping. With everything on (lights, heater, inverter (idle), etc.) I'm burning around 6 or 7 amps. I've been leaving the lights, heater, and fan on all night and coming back the next morning to see only a moderate drop on the battery. So I'm now guessing that I would have been fine with a 4S2P battery (120Ah) rather than the 180Ah setup I currently have.

6. Preliminary testing with the microwave shows that I'm drawing over 100A with everything on. One of the cables I made that goes between the circuit breaker and relay is getting pretty warm in this test, so I'm going to make a better cable. So far I've only been running the microwave about 3 minutes at a time and I noticed that it draws down the voltage below 12V at times. I attribute this large voltage drop to the bad cable not the battery. This is one situation where having the AGM battery in parallel would be good. It will be able to kick in whenever there is a large load on the battery and should keep the voltage stable.

7. One quirk that I need to fix is that the battery separator (made by Sure Power) connects the van battery when the house battery voltage is over 13V. I guess they did this so the inverter/charger would charge the van battery too. But in my case it's a problem since the van AGM battery (and van) stay connected after I turn off the charger and draw almost 1A. I can only get it to dis-engage the separator coil by turning off the Lithium battery (via PowerMon) and turning on something in the van like a rope light or fan. I looked at the separator and noticed two connections ("start lamp" and "start signal") are floating. So I hope I can find a way to set this up so it only connects the batteries when the engine is running.

This update is getting long, so I'll leave it there for now. I'm in the middle of re-locating my new AGM battery into the van and will equip it with a monitor and relay so I can turn it off and on as well. Will follow as I get further into this..

Hope it's helpful for other who might attempt something similar..

[markopolo]

kite_rider - does your van have two alternators?

Do you know if the PowerMon can be set to disconnect based on temperature?

You could replace the Sure Power separator with something like Victron's Argofet 200-2 isolator if you only want the chassis battery to charge while the engine is running and not while on shore power. Related topic here: http://www.classbforum.com/forums/f2...late-8292.html

[kite_rider]

Thanks for posting the link about the issues with the battery isolators and lithium batteries, it's exactly the issue I have with the Sure Power separator.

Per your questions;

1. My van only has one alternator, it's the upgraded 220A version.

2. It doesn't look like the PowerMon app has a disconnect on temperature feature. I'm still playing around with it and there are a TON of settings and options. I can (dis)connect on over/under voltage, over current, variable levels of battery charge per the 'fuel gauge', plus a ton of timer based options. The temperature based disconnect would be handy in preventing charging when the battery is under 32F. Thornwave appears to be a small engineer based micro-company so I may be able to talk to the developer and get this feature added to the app.

3. Regarding the separator I'm thinking there are a couple of options for me.

Option #1: Switch the 'ground' signal on the separator between 'float' and 'ground' based on ignition. It isn't clear to me that this separator (Sure Power 1315-200) will disengage when the ground signal is disconnected from the ground, but if anyone knows this to be true, please let me know!

Option #2: Just use a plain old heavy duty relay (one I already have lying around from my VW Eurovan) switched on with ignition. It looks like this is what others have done on the forum.

I'm looking into the Victron FET battery isolator. I'm not sure what this will buy me over the plain old relay, but it's an interesting possibility.

[Luv2Go]

In an earlier post I mentioned I would post the results of a full discharge. Well, last week I unintentionally discharged the lithium pack to where the inverter shut off (UVLO set to 12V) by running a 800W heater on and off all night. Unfortunately, at least with my setup, the lead acid battery only discharged 3%.

I think part of the issue is I have wiring between the two banks that supports only 30A and the inverter was drawing about 80A, so there was quite a bit of voltage drop between the two banks. I think the second issue is that the lithium battery voltage didn't dip down to the point where the lead acid battery could be drawn from until the very end:
InverterVoltage.jpg

BTW, the pack is over two years old at this point and the A/H discharged per the Thornwave was 327, so the capacity of each cell was over the 80A/H claimed capacity, and due to the high current when the heater was on, they were not discharged all the way. Routinely this pack gets subjected to 14.5 to 14.6V while driving for hours due to our stock Chevy alternator's high output voltage. I do not disconnect with high voltage automatically. I have read dire warnings that floating your lithium pack at these levels will produce lithium plating and drastically reduce the capacity and increase internal resistance (which would show up as bigger voltage drops with high current than I had, approx 4 milliohms). So far I have not seen this, it may just be luck.

[markopolo]

It could also be that both battery types were indeed sharing the load in the later stages. When the 12V UVLO was triggered the lithium then ended up charging the lead acid battery. Without looking it up - I think 12.8V for example would be a LFP battery at approx 20% SOC and a lead acid battery near or at full charge.

[Luv2Go]

Originally Posted by markopolo

It could also be that both battery types were indeed sharing the load in the later stages. When the 12V UVLO was triggered the lithium then ended up charging the lead acid battery. Without looking it up - I think 12.8V for example would be a LFP battery at approx 20% SOC and a lead acid battery near or at full charge.

Unfortunately not. The Thornwave monitoring the lead acid was at 97% at the conclusion of the discharge. The graph was not interesting so I didn't post it.

[kite_rider]

Originally Posted by Luv2Go

Attachment 6958

Routinely this pack gets subjected to 14.5 to 14.6V while driving for hours due to our stock Chevy alternator's high output voltage. I do not disconnect with high voltage automatically. I have read dire warnings that floating your lithium pack at these levels will produce lithium plating and drastically reduce the capacity and increase internal resistance .

I'm also using the Thornwave PowerMon, but it doesn't produce graphs like the one you've shown. How did you get that?

Per your comment about overcharging the battery pack; I think it's actually worse to overcharge than to disconnect the battery pack. Maybe I'm misunderstanding something here, but I've never heard of a problem with floating a lithium battery pack. I have heard many people say that constantly charging a lithium pack to 100% SOC will reduce it's life. So I'm using the Thornwave PowerMon to disconnect my Lithium pack when it gets to 14.4V (measured at the battery) for a duration of 3 seconds.

I have heard that it's not good to disconnect a battery abruptly from an alternator during a heavy charge, but that doesn't seem to be the case here. You are still connecting that alternator to the chassis battery, right?

[kite_rider]

To follow up on this thread; I've been doing some field testing with my parallel lithium / AGM setup and have observed the following;

Testing on my 'DIY' Lithium battery for about a week of camping in sub-freezing temps (between 14-23F) I'm charging the battery from the stock Promaster 220A alternator and noticing a peak of about 75A, but an average charge of around 55A. This alternator is also charging the chassis battery, house AGM battery, and providing power to run the van.

The PowerMon battery monitor is programmed to disconnect the battery after it reaches 14.4V for a continuous 3 seconds. The it re-connects at 14.0V. Overnight power usage has been between 25 - 40Ah of energy and the charge cycle (when driving) usually lasts between 25 to 40 minutes before the PowerMon disconnects the battery. The Low Voltage disconnect is set for 12.8V for a duration of 5 seconds; but so far this hasn't occurred. The closest I get is when the microwave oven is running, but it doesn't trip the LVD. There isn't currently a setting on PowerMon to disconnect when the temperature is below a certain threshold, but since the batter is positioned near the glycol boiler and since I always have the heat on, the reported temp has been a constant 70F giver or take about 4 degrees in either direction.

The monitor on the house AGM battery shows that it absorbs about .2A when the Lithium voltage is at 13.3V or higher, but seems to go to 0A when I'm around 13.1V. The only time I've seen any current go out of this battery is when I'm cooking stuff in the microwave oven.

I was concerned about the Sure Power battery separator keeping my coach and chassis batteries connected while the lithium battery is 'on', but now I'm less concerned because it doesn't seem to drain the lithium battery as much as I feared. So for now, I'm leaving it in as it was from the factory.

[Luv2Go]

Originally Posted by kite_rider

I'm also using the Thornwave PowerMon, but it doesn't produce graphs like the one you've shown. How did you get that?

The graph comes from Domoticz. I reached out to Raz (the owner of Thornwave) prior to my purchase and he agreed to share the protocol spec of the monitor so I could write a LUA script to read the data into Domoticz. The script has been downloaded more than ten times so I suspect someone is actually using it (other than me).

Originally Posted by kite_rider

Per your comment about overcharging the battery pack; I think it's actually worse to overcharge than to disconnect the battery pack. Maybe I'm misunderstanding something here, but I've never heard of a problem with floating a lithium battery pack. I have heard many people say that constantly charging a lithium pack to 100% SOC will reduce it's life. So I'm using the Thornwave PowerMon to disconnect my Lithium pack when it gets to 14.4V (measured at the battery) for a duration of 3 seconds.

Agreed, I also have read many posts/articles that say constantly floating a lithium pack will reduce its capacity more quickly but I've also heard that LiFePO4 packs are less affected by this. Unfortunately I have no links for said posts/articles.

However I have had real-world experience with two lithium packs in RV coach battery applications, one Thundersky and this one, which is a CALB clone. The capacity of CALB clone I mentioned above. With the Thundersky I floated it at 14.6V for about a year while it was new, until I started reading that this was not a good idea. Then I lowered the float voltage to about 13.6. After about 4 years I did a capacity test and found out that the capacity was actually over 25AH higher than the rated 400AH for the pack! So floating at 14.6V did not lower the capacity of that pack noticeably.

So my experience is that floating at high voltages does not significantly affect the capacity, at least of my two packs. YMMV.

Originally Posted by kite_rider

I have heard that it's not good to disconnect a battery abruptly from an alternator during a heavy charge, but that doesn't seem to be the case here. You are still connecting that alternator to the chassis battery, right?

The original Roadtrek coach battery is still in place so both the coach and chassis battery remain connected when I disconnect the lithium pack.

[kite_rider]

Originally Posted by Luv2Go

The graph comes from Domoticz. I reached out to Raz (the owner of Thornwave) prior to my purchase and he agreed to share the protocol spec of the monitor so I could write a LUA script to read the data into Domoticz. The script has been downloaded more than ten times so I suspect someone is actually using it (other than me).

Very cool. I don't have a Domoticz, but I had noticed the 'data out' pin on the Thornwave PowerMon and have consider asking for the data protocol so I could data log on a Arduino. Nice to see that Raz was open with this, makes me glad I chose to buy his product.

I'd like to reach out to Raz and request an additional feature in the PowerMon app where I can cut off the relay when it notices charging below 32F (programmable preferred). It would make his app very handy for Lithium pack management.

[Luv2Go]

Actually I'm connecting to the device with Bluetooth, the RPi 3 has built-in Bluetooth capable of communicating with the Power Monitor. For me, the neatest part was that I didn't have to run wires from the monitors to the RPi and the Bluetooth wireless communication is quite reliable given the small distances in the van.

To reach out to Raz, I used the contact link on his website. He seems quite busy so you may have to contact him a couple of times to get an answer.