Dual Batteries with Lithium - a cryptozoological study

[KevinK]

I've read every thread I can find here and on other forums for the past two months, and there is very little on the topic of running a dual battery setup with a combination of lead acid starter battery and Lithium house battery. I have in fact not found a single example of what I'm trying to do, and that surprises me. Perhaps barring some Redac systems in Australia that I still can't find any actual details on.

I've found intrepid souls that have gone 100% lithium and designed very intricate and amazing systems from scratch.

I've found people who talk trash about lithium until they're blue in the face.

I've seen comparisons of amp hours, watt minutes, unicorn farts, voltage drops, charge times, impedences, leprechaun sizes, Cs (capacity, degrees and Coulomb, not the speed of light), heat tolerance, 12,24,48,96,192,384 and 6144 volts (maybe not quite), and I'm done with all of that.




We're going lithium for our second battery in our dual battery setup - this thread isn't about choosing if that's a good idea.


I would like to discuss the difference between the two possible ways of charging the Li battery - simply put, should we use an inverter and a battery charger for the Li battery, or just do the simple alternator isolator system and treat the Li battery like a lead acid?

The manufacturer of our particular battery suggests their Li batteries are "‘plug-and-play’ replacement modules for lead acid applications." But then I see things like this LiFePo charger from Redarc in Australia, and wonder if I still need something like that since these batteries have built in BMS? The Redarc charger implies that the charger is still needed even if a battery has BMS, but is that old information? I haven't called Redarc yet, but plan to.

Since I like to draw pictures in order for me to understand something better, I'm looking for pros and cons specific to the performance of the two options pictured below (I know one system is going to cost more). I drew in the positive and negative legs for each run just so my simple mind could follow the flows. I know that ultimately where you ground can be different and only the positive lead really needs to be switched, but I'm semi-feable, so bear with me...


Standard dual battery setup:

AC Charger dual battery setup:

In the interest of making this thread easy for others to find in the future, here are some key words I've used to find information:

dual battery, lithium, LiFeMgPO4, LiPo, lithium iron, LiFePo, charger, alternator, inverter, lead acid, agm, Ahr, amp hour, bms, battery management, isolator, dc-dc

 

[Joe917]

http://www.technomadia.com/2015/02/living-the-lithium-lifestyle-3-5-year-lithium-rv-battery-update/

 

[DiploStrat]

I'll Play

With the caveat that I did NOT buy lithium ion or iron batteries specifically because I could not get reliable information on their charging requirements:

-- The BIG issue is this, in recent years everyone has waked up to the need for relatively high charging voltages for lead acid batteries, so we have seen charging voltages go from a nominal 13.9v to 14.4v with EQ cycles as high as 15v+. The result has been much better battery life and performance with lead acid.

-- There is some anecdotal evidence that lithium batteries may need lower charging voltages, thus creating a conflict. (See Technomadia, among others.)

-- The problem is that there are many different purveyors of many different lithium cells, many buying 2v cells in China and boxing them with their own BMS/control circuits. Some may be good, some may be trash, I for one, don't have enough experience to judge.

-- The Redarc box, a form of B2B (or DC-DC charger), like its competition from Sterling Power and others, seems to be aimed at addressing the problems of new Euro alternators that shut off from time to time and assist in regen braking. (I believe that some Ford F 150's use these in the US.)

-- I have a friend who runs Lithium (from AM Solar) in an older Tiger built on an Astro van. Last I looked, he was reporting great things using an automatic charge relay. BUT, might his older Chevrolet have tamer voltages? Does this matter? I don't know.

-- I don't think your AC/DC conversion exercise gets you anything unless: 1.) You know that your vehicle's native charging system will NOT work, and 2.) You know that the AC powered charger does have the correct profile for your lithium battery.

IF, repeat, IF, your Lithium battery is really plug and play, then an automatic charge relay may be all you need. The conversation really begins with the battery vendor. And for that conversation, you need to know the charging voltages of your vehicle.

Best I can offer. Hope it is correct and useful.

Good luck.

Edited to add: Joe beat me to the link! ;-)

 

[DaveInDenver]

http://www.technomadia.com/2015/02/living-the-lithium-lifestyle-3-5-year-lithium-rv-battery-update/

This is a great post to study.

Key points are LiFePO4 can be substituted for a standard 6-cell lead acid for the most part but you have to consider the charge and discharge curves and operating temperature a bit more closely, it's less tolerant of overvoltage (particularly long term float) and temperature extremes than lead acid.

Also while it's a relatively safe lithium chemistry it's still possible to make them unstable and ignite.

I think the primary concern using a mixed system will be that voltages are going to be critical and there's a fairly good chance you'll either undercharge the lead acid or overcharge the lithium, at least over time, which may start to impact expected life for one or the other.

 

[KevinK]

thanks guys! yeah Technomadia definitely played a part in our decision to go LiFePO, and is one of those intricate and amazing systems designed from scratch that I studied.

temperature concerns are one reason we plan to not install under the hood - it looks like heat is the biggest enemy of life expectancy, and we live in Arizona.

At this point, I think my biggest question is whether or not our stock alternator, which is supposedly rated at 100 amps, will push too much more than the recommended 20 amps the battery asks for in charging. I see people talk about high voltage concerns more often than high amp concerns.

I also need to throw a meter on the alternator to see exactly what voltage it really puts out - it's a 2014 Toyota Tundra (I think all models in this year are the same), as the battery is rated to accept between 13.8-15.2 with a preference for 14.6.

 

[dwh]

The problem is that lithiums don't need or want an absorb stage or a float stage. You push them to a specific voltage and that's it, turn off the charger, you're done.

The primary function of the BMS is the same as a solar charge controller - to prevent overcharging.

So, as long as your vehicle supplies adequate voltage, then just let the BMS handle it, which is the whole point of the drop in plug and play battery to begin with.

So a simple split-charge relay or ACR should work fine.

 

[jonyjoe101]

my observation on lithiums is that they perform similar to lead acid while charging. I have a 94 amp hour 3s lithium battery (max voltage is 12.6) it does have a BMS circuit that will shut off charging power to it after it reaches 12.6 volts or one of the 3 cells reaches 4.2 volts. As long as your battery BMS can handle the charge current it should do ok to connect to alternator. The BMS will protect your lithium battery from overcharging and discharging, so basically you can treat it like a lead acid.

I dont have mine connected to the alternator, its all solar. I do use my ecoworthy 20 amp mppt (which is not lithium capable, but reduced the absorb voltage to 13 volts which is the min for the controller) to charge it and never had any problems with it. Unlike an agm battery which only accepts maximum amps at the beginning of the charge, the lithiums will take all the amps you can give it until it reaches about 90 percent then the amps start to drop slowly. The last 10 percent will take many hours to reach, no matter how many amps you have available. So unless you do alot of driving you might never reach a full charge. But with lithiums, they will actually last longer the less you charge them, for my battery if I can get it to 12.3 volts at the end of the day its good.

I also done the RC charger route in trying to charge my lithium, connecting a triton 2 rc charger (lithium capable) powered by my agm battery. But the triton is limited to a max of 7 amps output and the charger got very hot when in use, and doing it this way it would drain my agm battery and heat up my van. It was inefficient and it would take many days to charge the lithium. With the ecoworthy mppt its just like charging my agm, very efficient. At the end of the day my battery is usually over 90 percent charge.

Originally I was just going to run the 94 ah lithium as a backup to my 102 ah agm because of the charging concerns, but have recently unplugged the agm and now only use the lithium as the house battery, it literally has double the usable capacity of the agm at less then half the weight. I can go several days between charging it. The BMS on the battery lets me treat it like a lead acid battery. From my own experience no expensive special lithium charger is needed. But I do recommend some sort of LED/LCD voltmeter on your lithium so you can monitor the voltage all the time, just in case.

 

[KevinK]

This is exactly the real world info I've been looking for. Thanks a bunch!

We do drive 10-12 hours a day when we're overlanding, and that's what made me think about too much float voltage time, but it sounds like the BMS will just take care of itself.

I'm about to order the Blue Sea ML-ACR and start going for it.


Sent from my iPhone using Tapatalk

 

[DaveInDenver]

At this point, I think my biggest question is whether or not our stock alternator, which is supposedly rated at 100 amps, will push too much more than the recommended 20 amps the battery asks for in charging. I see people talk about high voltage concerns more often than high amp concerns.

Voltage is critical with lithium and specifically the voltage is usually a must not exceed. They can be charged effectively even if the charge voltage dips, which is unlike lead acid, but only to a point. Chronic under voltage on a lead acid will lead to sulfation but there's no analog to this with LiFePO4. If the charge voltage dips too far the battery just doesn't fully recharge, it's not damaging.

You really need to just be concerned that the cells do not get overvoltage. The management box should take care of disconnecting the cells, so follow whatever requirements the module manufacturer suggests (probably a max and min voltage and time). That's the idea behind the drop-in configuration, it should take care of things for you and if the BMS designer is astute the design will allow for normal use with typical worst case, which is probably a harsh battery charger that pulses for desulfation. But I'd check and follow whatever they tell you their BMS does.

Current for both chemistries, really all batteries, is always as a function of voltage and what type of profile you're following and which stage in the cycle. Your alternator will source more than enough current to reliably charge a LiFePO4 battery, don't worry about that. The concern is the charging system on vehicles is fairly indiscriminate because lead acid batteries are forgiving and intrinsically safe.

 

[FJR Colorado]

I see you live in AZ...

Do you park outside?

Why not just charge the LiOn battery via solar?

Make it a discrete system...

I'd like to hear if the LiOn works any better than a deepcycle AGM (which works amazingly well).

 

[DaveInDenver]

I see you live in AZ...

Do you park outside?

Why not just charge the LiOn battery via solar?

Make it a discrete system...

I'd like to hear if the LiOn works any better than a deepcycle AGM (which works amazingly well).

Interesting idea. I think the main criteria would be if solar is sufficient when traveling, too. Unless charging only during camped and parked works in the plan. It will be neat to see what happens with KevinK's system.

I'm not convinced it's worth it for a single house battery where the weight and bank capacity pros aren't huge over a same size AGM in light of the significant cost difference. There are other advantages, longer life and flatter discharge curve that are potential improvements, but hard to say in this application if it will prove to actually be any different.

Particularly the longer life has me curious because lithium ion is fairly demanding about the charge tolerance, which of course is really a question of the quality of the management, and the alternative is that quality and understanding of battery handling means it's not unusual for an AGM to last several years now.

Also the ability for the modules to handle the abuse of driving off highway is a question to me. Optima pioneered the idea that batteries need to be mechanically strong for off highway use and Odyssey, Northstar, etc. have run with. I don't know that Valence or whomever haven't considered this type of abuse, but there's more going on now than just lead and fiberglass mat in an electrolyte. The BMS is another computer and one that is fairly critical.

 

[FJR Colorado]

I have a discrete solar-only system in my Tundra. 100W Renogy panel & controller. YellowTop deep cycle battery. It works astonishingly well. Just runs...

Of course, you need a sunny place like CO. No place sunnier than AZ...

That KevinK makes a mean GIF drawing! I liked that...

 

[KevinK]

Solar is a great idea FJR, and it may find it's way into our build someday. One thing I've heard is that heat reduces the efficiency of solar, so trundling around the desert at 125* probably won't be as efficient as driving across mountain passes when it's sunny. We also drive quite a bit so our engine is usually running for 8-10 hours a day when we uberfart. If our camping style becomes more sedentary we may add a panel or two.


The amount of driving we do brings me to Dave's point - it probably doesn't make much sense to go through the expense for one LiPo when the weight difference isn't as significant as it would be if we were building a bank. Our 40Ah LiPo is 14 lbs. To get that many usable Ah in AGM, we’d need about 60 lbs. 46 lbs difference doesn’t seem like much on a 6 or 7 thousand pound machine, but I’m a little bit of a lunatic.


‘I believe in getting lightweight through elegance of design'
And
‘Any car which holds together for a whole race is too heavy’

~Colin Chapman, probably

This has lead me to spend far too much money on things that do not exist. I’ve literally been buying parts that have fewer molecules, and giving suppliers more dollars for them - even to myself this sounds outrageous. But the end result is that our aluminum nitrogen tank weighs 25 lbs instead of a steel one at 35. Our bedslide weighs 88 lbs instead of 120. Our battery is 14 lbs instead of 60. The tent is something something lighter than the ruggedized beast we looked at. Every item or system we install has a direct effect on our ability to get where want to go, both in cost of gas and shear capability off road. The more stuff we have to lug around with us, the fewer spots we can physically access - and every pound does add up.


We’re also interested in Dave’s other two points - longevity of cycles and resistance to having the **** beat out of it. We’ll be mounting the LiPo away from the underhood heat. Probably in a container in the cab. 160*F underhood temps are not uncommon when idling in the middle of the desert trying to get yourself or a buddy unstuck. One thing that did impress me, and ultimately turned us to Valence as our battery of choice, is their use in Border Patrol vehicles. We’ve had Border Patrol escorts through some backcountry areas, and those guys don’t drive slowly or gently.




To make a short story long, we’re interested to see how this goes, and will keep updating this thread as we go. I might even remember to post some install pics or videos if I haven’t had too many beers while I’m working and forget.


For entertainment, here’s what our typical overlanding drives look like.


https://youtu.be/jfjBKdfWYMw?list=PLjF5T--ma36nwz4qdAJivEUUj3xtnTOJ6

 

[KevinK]

I finally ordered the last set of parts for this setup.

On the battery manufacturer's recommendation, we're just going to drop the LiFePo into the system like it was lead acid and see what happens. It will have a voltage meter on it so we can keep track of it's performance initially and also over time. I'll try to keep good tabs on the usage stats as we go and post them in here.

We elected to mount the battery in the cab of the truck where we're removing the rear seats for the fridge, water system, electrical distribution, storage and a comfy cushioned platform for the dogs to ride on. Inside the cab should have the most stable temps which seems to be the biggest killer of LiPo batteries.

Based on information found here on ExPo and in discussions with other overlanding friends we're running a Blue Sea ML-ACR with remote switch for manually connecting the house and starter batteries for self jumping. 2/0 cable for + and - runs between the batteries with a 250 amp fuse on each end of the positive leg. Blue Sea fuse block for distribution from within the cab.

I'm looking for a decent 750 watt inverter right now to run our 600 watt coffee maker - open to suggestions if anyone has 'em.

 

[Haf-E]

The Valence battery product is interesting in that is uses a chemistry which gives a nominal voltage of 3.2 volts per cell - so with four of them in series it ends up equaling 12.8 VDC - very similar to a lead acid type battery at 12.6 VDC (using six cells in series). That make operating it in parallel with a lead acid battery much simpler.

Other lithium battery chemistries are not as fortunate to have the same voltage - for example, the Nissan Leaf uses a battery that has a nominal voltage of 3.75 volts per cell - so with four in series the total voltage equals 15 VDC - and three in series equals 11.25 VDC - Too high and too low.

Interested to hear how this works out!