2108DS Lithium install: the trip report

[tinglett]

Happy camper here! We took the 2108DS out for a weekend camping trip at a close-by state park to try out the new batteries before our season is totally done.

The weather forecast was pathetic -- each day expected to dip below freezing, rain, maybe snow or freezing rain. Blech. We went and the weather was actually ok. It did get below freezing which worked the furnace a bit.

We were dry camping, of course, with no inverter. So no TV or microwave use. I have a cpap, but have a DC power brick for that (was worth the money). In general we'd have only 1 light on, but we weren't so picky we couldn't turn another on for the bathroom, etc. The fridge was running on propane, but it must have a fan or similar as it seemed to be mainly drawing about 0.8A fairly continuous (we did run it on shore power to cool it down in advance). The furnace draws about 4A and I'd say it ran every 45 minutes for maybe 5-10 minutes each hour at the coldest part of the morning.

After the first full day we had consumed 42.1Ah as you can see from the attached Victron BMV screenshot. This was only about 21% of our total 200Ah. I'm pretty happy about that. Day 2 was nearly identical for power use. And note these batteries can be drained to near zero so it seems we can get perhaps 4 days in without a recharge. I'm thinking a couple 100w solar panels may be able to keep these batteries topped off. That's a project for next year.

The only thing weird was that after driving home the Victron BMV thought the batteries were 100% charged. That was impossible as the drive was less than 1 hour...and they are charging on shore power at about a 31A rate right now. So I need to adjust something on the BMV, or need to learn my procedures better.

 

[creativepart]

Sounds good. Battery monitors that monitor amps sure do help.

I've found I needed to calibrate my BMK app.

There is a calibration setting in the app. Click on the "GEAR" icon in the top right hand corner and then click on "Battery". Scroll down and you'll see a SOC number that you can alter to set the true SOC.

Make sure it's setup for Lithium batteries and fully optimized.

Here are the setting for your Victron for Battleborn LiPo4 100 amp batteries:

From: Battle Born Batteries <[email protected]>
Subject: RE: Question re Victron BMV-712 Battery Monitor settings for 100Ah BB.
Date: February 22, 2020 at 12:11:21 PM EST
To: Bruce Colman <[email protected]>

Thank you for the support.

The setting you request are attached below.


01 Battery Capacity — 100AH *
02 Charged Voltage — 14.2v *
03 Discharge Floor 0%
03 Tail Current — 4.0%
04 Charged Detection — 03
05 Puekert Exponent — 1.05 *
06 Charge Efficiency Factor — 99% *
07 Current Threshold — 0.10A
08 Time to Go Averaging Period — 03
09 Zero Current Calibration — ZERO
10 Synchronize — SYNC
11 Relay Mode – DFLT

Once your done applying these settings under the battery tab you’ll want to go into the Relay tab. In the Relay tab you’ll select Low SOC Relay and disable that. Bring the battery to a complete state of charge and that will auto sync the BMV unit.

 

[tinglett]

Awesome, thanks!

The 81Ah used on this trip was charged up in just a little more than the calculated 2.6 hours @31A (like maybe 15 minutes more). So the Ah readings were correct, and should be as they are pretty much wired into the shunt characteristics, I suppose.

I think the main problem was that I had the default for Charged Voltage. It was something like 13.x volts. I suppose the Victron saw that voltage for 3 minutes at low amperage from the tow vehicle and voila, must be charged, right? I'm wondering now if my car is going to produce the 14.2v to convince the Victron that it's charged it up on a long drive. I doubt that's gonna happen enough to matter, though.

It was nice to see the new PD charger working correctly. I heard the fans running occasionally as I checked in on it. They are pretty quiet.

Now I need to decide what to do for winter storage. I've been told by the Battle Born guys to completely disconnect the battery so it doesn't discharge. Even the Victron BMV will draw too much. They say min temp of -15F on their website, but he told me lower is ok provided I'm not moving them around and they are completely disconnected. He still gave the advice to pull them and store somewhere inside as the better answer.

 

[creativepart]

That brings up the question of your Alternator. What are you doing to accommodate the Alternator's charging of the LiPo battery?

Some use a battery isolation device. Others add DC to DC charger between the alternator and the battery.

Doing neither is an option some choose, but most caution against that.

 

[tinglett]

That brings up the question of your Alternator. What are you doing to accommodate the Alternator's charging of the LiPo battery?

Some use a battery isolation device. Others add DC to DC charger between the alternator and the battery.

Doing neither is an option some choose, but most caution against that.

Hmm...I'm feeling I'm about to learn something. Remember I have a TT connected to the TV via a standard 7-pin towing connection. Is there something special I need to do for LiPo? It's seems I chose "neither" by default!

 

[DavidEM]

I didn't follow all of the Victron screen shots and data above, but one reason that the Victron may be prematurely showing 100% charged is that there is a setting for amp hour capacity of your batteries and it looks like the default is 100 Ah. Change it to 200 Ah and it should not show prematurely fully charged. I do think that it will figure it out on its own (a Xantrex battery monitor I had did) after several discharge/charge cycles.

David

 

[creativepart]

Hmm...I'm feeling I'm about to learn something. Remember I have a TT connected to the TV via a standard 7-pin towing connection. Is there something special I need to do for LiPo? It's seems I chose "neither" by default!

Hummm, you bring up a new question that I've not seen discussed.

In motorhomes, where the engine alternator charges both the Chassis battery and the House batteries, the switch to Lithium puts a strain on the vehicle alternator.

The problem is the majority of alternators rely on the fact that lead acid batteries increase their internal resistance as the battery gets charged up. So, the vehicle alternator can only push so much power into the lead acid battery bank.

But when you switch to Lithium the battery doesn't ever increase it's resistance. That's one reason they can be recharged so quickly. And, when an alternator is pushing power to the batteries the battery keeps taking it. When this happens the Alternator can easily overheat and even burn up as the battery tells the alternator to send more and more power.

Again, in a motorhome, people deal with this by a couple of ways. One inexpensive option is a BIM, battery isolation manager. The BIM keeps the Alternator connected to the battery for charging and than after some time passes disconnects the battery from the alternator to give it a chance to cool off. Then it reconnects the two a little bit later. It does this automatically.

Another method is to install a separate 12v charger just for the Lithium batteries. It has a specific Lithium charge profile. This charger is connected to the alternator. It's a "DC to DC" charger. It limits the amount of power taken from the alternator to properly charge the batteries.

BUT!!

What about travel trailers? I assume they will need one of these two devices or something similar.

I think when Lithium batteries started selling at $1000 a battery the manufacturers anticipated they would find most of their buyers in the expensive motorhome market - so, I have not seen this specific discussion in travel trailers.

 

[tinglett]

I'll do some experimenting and will probably end up calling Battle Born as well. I'll need to use up some charge so I can see what the car does when I connect. I really wish I had thought of checking the app this weekend.

What's got me puzzled now is some automotive engineering. I'm sure the 12v pin of the trailer connector is fused at probably 10A, but how does it actually produce a maintenance level of current? I'd think the LiPo batteries would love to get 200A if they could! Considering my fuse didn't blow nor did the wires melt, I assume the car has a circuit that limits the current. This is probably basic EE101 that I don't understand (yet).

I do unplug the cable when I unhitch, mainly for fear of forgetting and driving away. So I have a natural "isolation" mechanism in this respect. It's possible the car also has some mechanism to avoid drawing power from the trailer connector when it's not running. If I recall that's not true of cigarette lighter sockets -- they can trickle charge a car I think. Or at least at one point in time they could.

 

[tinglett]

it looks like the default is 100 Ah. Change it to 200 Ah and it should not show prematurely fully charged. I do think that it will figure it out on its own (a Xantrex battery monitor I had did) after several discharge/charge cycles.

I did set the 200Ah as that's the first thing the Victron-BMV forces you to do (maybe the only thing). I also set the puekert exponent as the manual mentioned that needed to change for LiPo. But I didn't change any of the other stuff. We'll see if that cured it. I suspect it did, but it'll take a real trip to know for sure.

 

[creativepart]

I assume the car has a circuit that limits the current.

That's the problem. You car does not have any kind of regulator to limit the output. The Automaker knows that 12v batteries produce such I high resistance to further charging when they are at or near fully charged that the alternator couldn't put more power into it if it want too.

You Lithiums... nope. They don't do that.

The Lithium battery companies love to call them "drop in" replacements. But that's not proven exactly true.

 

[DavidEM]

I think I can answer your question about TV charging of a lithium battery based on my measurements of charging via the 7 pin connector to a 80 Ah FLA battery and some limited knowledge of LiFePO4 batteries:

My trailer battery would charge at 10 amps through the 7 pin connector when the trailer battery was half full and at 4-5 amps when it was 80-90% full. First my TV and I think almost all TVs with factory installed hitch and 7 pin connector only produces current when the engine is running. There is an ignition triggered relay that does this.

But why doesn't it charge faster? Well the main reason is that the wire is 10 gauge and it is long, probably 20' from the alternator back to the trailer battery. When it is drawing 10 amps, there is a 0.4 volt drop. Subtract that from the alternator's fixed voltage of 13.8 and that doesn't give enough to push any more amperage.

Then kick it up to 30A (the circuit is protected by a 30A fuse) and assume that it is charging a lithium battery and you get 1.2 V drop or 12.6 at the battery. I suspect that voltage is not enough to push 30A into a lithium battery. So it is self regulating due to the wire size and length. If it did possibly push 30+ amps it would blow the fuse.

David

 

[tinglett]

David, that makes sense to me and I hope is either correct or there's some other fancy circuitry to protect the car. I did go out and measure the +12v while the car was running (mine does indeed need to run) and it's still producing 13.8v. So I didn't blow out a fuse yet!

This seems to answer one of my questions, though. If the alternator only goes to 13.8v, my updated Victron BMV settings won't think it is fully charged as I told it 14.2v. I think that's ok as it'll count the Ah until it reaches 100% and stop there if I'm driving all day.

This may also answer another question looming in the back of my head. Can you jump a LiPo battery with jumper cables? This seems like a VERY BAD IDEA to me based on this conversation. That smokin' alternator comes to mind!

 

[al1florida]

I would do a test by first draining my house batteries down to about 50% SOC. Next hook the trailer up to the car, run the engine up to about 1500 RPM, so the alternator is putting out about the max it can, and see what voltage & amps the Victron is showing at the battery. Also have a voltmeter on the car battery to see what the alternator is putting out.

This should give you all the numbers you need to know exactly how everything works together.

 

[thataway4-WO]

This may also answer another question looming in the back of my head. Can you jump a LiPo battery with jumper cables? This seems like a VERY BAD IDEA to me based on this conversation. That smokin' alternator comes to mind!

Yes, this is a very bad idea. There are specifically designed jump boxes which use Li batteries, but their management is much different than Battle Born.

Please see my comments in the other thread. Thanks.

 

[al1florida]

Yes, this is a very bad idea. There are specifically designed jump boxes which use Li batteries, but their management is much different than Battle Born.

Please see my comments in the other thread. Thanks.

Why is it such a bad idea to use a pair of jumper cables to jump over to another battery?

I believe the lithium batteries are capable of a 15-30 second discharge of 200-300 amps per 100AH battery. Besides just how much current can you get down jumper cables with #8 or #6 wire and alligator clips attaching to the batteries on both sides of the jumper cables.

A couple of time I jumpered from my 400AH lithium battery pack to start my Chevy Colorado after it wouldn't start after a couple of days towing the truck. It has been a few years since I had to jump the truck.

 

[tinglett]

Next time I call BB I'll ask about jumping. I was thinking more about using jumper cables to charge the LiPo batteries at a high rate vs starting the car. Bob pointed out the Sterling battery-to-battery chargers (in my install thread) that I should look into for that scenario. But starting the car is valuable also. What if I'm stuck on some forest road with nobody around? Knowing if jumping will work vs. destroying the batteries, and perhaps the TT, would be nice to know in advance!

 

[DavidEM]

I think jumping dead LiPO batteries with jumper cables connected to a toad's battery cables while the toad's engine is running shouldn't be a problem. Between voltage drop in the cable/connections and the relatively low (13.8V or so) toad alternator output should limit current. But check your alternator with a heat gun when you do it. If it starts to really get hot- 220F or more case temperatures, back off.

I also concur with Al's thoughts above. If the Li batteries are good to put out 200+ amps per battery for a few seconds then again voltage drop in the cable/connections should keep the current down to something reasonable. I would like to check it with a clamp on DC ammeter though.

At the very least, hook up the jumper cables and let the Li batteries charge up the toad's batteries for 10-15 minutes before trying to start it. That first ten minutes of charging a dead FLA battery will really suck up the amps and when combined with the starter draw, may be too much.

David

 

[thataway4-WO]

The issue is that thin cable will get very hot and even melt the insulation with high current draw. Heavier cables will carry more current--but also get hot, and some risk to the lead acid battery with the massive current surge.

In another post I mentioned that a several hundred amp Chinese copy of a German on /off switch basically melted when there was a surge load of about 200 amps (200 amp hour bank of battery) from the LiFePO4 bank to the inverter. This was a spectacular, and frightening event. I replaced it with the "real deal", switch which is able to handle 300 amps. When I am not using the Li battery bank, I want it disconnected from all loads and use a high amperage on off switch.

From my 200 amp hour battery bank to my 2000 watt inverter and return is about 10 feet, and I use 00 cables.

There are limiters (Battery Isolation Manager=BIM) which are used to allow Li battery charging from a RV alternator for 15 minutes and then cut off for 20 minutes. This prevents overheating of the alternator. These also will stop charging when the resting voltage of the Li pack is equal to or greater than 13.4 volts, and protect from voltage higher than 14.4 volts. For example, the Sprinter Alternator on my Via is 200 amp output. There are high out put alternators, such as the Leece Nevilles used on Ambulances or Fire Trucks. These start at 175 amps and go to 360 amps 12 volts, and 250 amps 24 volts. They have much more robust belts and cooling systems than many RV's have. Some of the larger diesel pushers will use this type of alternator.

The Battery to Battery charger is a bit different than the BIM, in that it functions just like any sophisticated smart charger, with a proper profile for the LiFePO4 battery. The charger is powered by the vehicle starting battery, rather than the 110 V mains power.

The Battle Born Batteries specifically caution about using the batteries for starting a vehicle. This is related to the battery management system---hopefully it would shut down the LiFePO4 before a heat/fire event or damage to the battery.

There have been some marine LiFePO4 batteries which are designed specifically for starting.
I suspect that there are also truck/ RV batteries also designed for this. The OP has the Battle Born Batteries which are not designed for starting loads.

 

[tinglett]

A follow-up. I had let the batteries discharge over the last couple weeks simply by not flipping the battery disconnect switch. It's amazing how that radio (the primary user of idle power) sucks away the juice. I hitched up to move the TT to prep for a trip this weekend and did a quick measurement via the Victron BMV to see how the tow vehicle actually charges the battery. See the numbers attached. Unfortunately I didn't take the time to check the tow vehicle battery terminals for voltage in order to see a drop. I believe I usually see something like 13.6v or 13.8v so there is definitely a drop. But I can see it's charging at approximately a 6A rate.

 

[DavidEM]

What you are seeing is typical for mostly charged up FLA batteries and evidently the same for Li batteries.

Try that experiment again sometime with almost completely discharged Li batteries. You should get up to 15 amps although the voltage drop will be double at that rate but the Li batteries should be able to take it at the lower voltage.

David

David