Batteries in a small van

[jpaddler]

And I thought the lithium batteries still had to go to 14.2 for bulk/absorption charge for some reason

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[John61CT]

No, only occasionally, if you believe in a "memory effect.

And even at 13.8V, you want to stop charging soon after.

And don't charge to (even that level of) Full, unless you've got loads running, ready to start drawing down.

If they're not going to be cycled for a while, they should be kept at a low SoC. But not so low that they'd risk going flat, self-discharge may be 2-4% per month (depends on temp).

And never put a charge in them when temps are freezing.

Lead is much more tolerant of abuse, with LFP those last two are death, little chance of recovery.

 

[jpaddler]

I'll keep that in mind, going to call balmar in the morning, and see if one of their voltage regulators will work with my set up

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[John61CT]

The adjustable one is MC-614, excellent unit for getting max amps into the batts without frying the alt, is charging many LFP banks out there.

Takes a decent "out of the box" auto or marine electrician to adapt your alt to external regulation.

But do NOT let your BB be the only batt on the output, if BMS isolates while alt is charging (no load dump), it will fry the diodes.

The DCDC charger route gives a lot more flexibility (solar, shore power) much cheaper overall too.

 

[jpaddler]

Which DCDC charger would you recommend?

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[John61CT]

The same two makes mentioned already several times above.

Sterling or ProMariner "battery to battery"

 

[jpaddler]

Ok.. I spoke with promariner tech support, and they said there stuff was preset, and not adjustable. I'll see what I can find out with sterling.

Thank you

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[John61CT]

Sorry thought they shared the B2B design with Sterling, like they do with shore ProNautic P line.

https://baymarinesupply.com/sterling-60-amp-battery-to-battery-charger-bb1260.html

Alan will answer your Q's, and the manuals are easily downloded.

 

[jonyjoe303]

From using lifepo4 for the past 4 months, and charging with my mppt controller, I notice they prefer high voltage in order to fast charge them. The 12.8 volt 110 ah lifepo4 I have wouldnt be getting any charge at 13.8 volts. I have 2 of these batteries and they both behave the same way. The sweetspot is something like 13.9/14.0 where you might get 1 amp going in.

Because of voltage drop I have to set the bulk voltage to 15.5 volts to fast charge them. And I float them at 14.5 volts. At that float voltage the battery reads about 14.2 volts and only gets less than 2 amps. 

I never paid too much attention to voltage with lead acid, but with lifepo4, if you try to charge them at 14.4 volts it will take a long time, to me that is the minimum you want to keep the voltage at. With lifepo4 the voltage seems to be more important in terms of how fast your battery will charge. 

Any dc to dc charger would have to at least be capable of supplying 14.6 volts to just get the battery up to 90 percent. 

With the namebrand lifepo4, with there heavy duty BMS they are more tolerant of whatever means you use to charge them. From what I read no special chargers are needed. The bms will handle any overvoltage problems.

 

[John61CT]

If you **define** 100% Full as stopping at 13.8V (3.45Vpc) it does not take long at all to get there from say 80% DoD at that voltage setting if you're able to charge at a high current rate.

Say a 180A charger on a 400AH bank, well under two hours will get you there. Of course your wiring better be right!

Working at the higher voltages you're talking about will **drastically** shorten the bank's lifespan, you may not even get to the 2000 rated cycles.

And you're not actually gaining anything, a capacity difference of just a few percentage points, at 13.8V will still be over the nominal 20-hour AH rating.

So if in daily use, under 7 years. If you're OK with that, do what you like, your bank.

But you can get much, much longer with gentler treatment, we don't even know just how long yet.

 

[frater secessus]

The following is for discussion purposes only.

Ok, so what can install between the starter battery, and the lithium battery bank, to stop it from going over 13.8 volts, but still get a decent amount of amps while driving?

Given that:

Alternator charging methods combine the batteries only at certain times:

• by 12v trigger.  Example:  low power 12v source that's only active when the key is in the RUN position.  These have 4 lugs:  starting+, house+, trigger+, trigger-; or, 
• by voltage sensing.  These usually have 3 lugs:  starting+ in, house+ out, starting-.  The starting- "ground" is only used to complete a low powered circuit so the relay can run itself.  So it's usually very thin.  

If you disrupt the trigger (or "ground") the relay cannot turn on, cannot combine the batteries.  Alternator charging of house batteries stops.  There is no effect on amps when the isolator is running.


So-o-o-o-o-o.....



You can:

Use a high voltage disconnect on the house side set to something very safe (13.5V?) that would disrupt the trigger (or ground) circuit.


Example:  you start out the morning with house batteries at 12.5v or something.  Drive to McDonalds for coffee and free wifi. 

On the way the alternator brings the house bank up to 13.5V.  The HVD disrupts the trigger (or ground) and the relay/isolator turns off.  

Caveat:  I am currently doing this on my van at ~13.7V even though I have golf cart batteries.  I do this to keep solar from pushing 14.7v into the chassis while driving if the batteries happen to be in Absorption.    This solution costs ~$15.  I am not encouraging you to do it.

 

[jpaddler]

I spoke with the guy at sterling power, and he recommended this.

http://www.sterling-power-usa.com/proconnect-cvsr70amp12vor24v.aspx

He said that the multiple charging steps that lead acid batteries needed, weren't needed for the lithiums.

Hopefully this might be the solution, for charging from the van while driving.

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[John61CT]

That's just an expensive ACR with a current limiting feature I suspect you don't need.

Any other good ACR will do, if your charge source"s) are all set to the LFP voltage (IMO 13.8 max), and you don't mind your cheap Starter getting that. See #26 for my reco in that category.

Otherwise you do need the custom voltage setpoint on LFP different from the primary charge source.

Only a DCDC, specifically their B2B charger will do that.

 

[jpaddler]

Ok... I guess he was thinking that the lithium battery might pull too many amps while charging, and damage the alternator.

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[John61CT]

The B2B will be limited already to the max amps rating depending on the model you buy, **and** give you complete control over the voltage setpoint.

Or the conversion to external regulation with MC-614 will give maximum amps output within the context of keeping the alt from overheating, between "small engine" mode and fine control using "belt manager" plus automatic temp sensor heat protection.

But that's just one charge source, B2B gives you that level of control and can be used with any old source you may want to tap into in the future, to me best bang for the buck.

Note an older version ACR from Blue Sea, CL-Series BatteryLink ACR (part# 7600) has a 60A current limiting function.

I just picked a NOS one up on eBay, so cheap I'm embarrassed.

Also, ​Xantrex Echo Charger has a 15A limit, too small for you, but FYI while we're at it.

 

[jpaddler]

Great, I'll check that one out..

Battleborn said they would like to keep the charging amps under 50, for a single 100ah battery, for battery life.

If I do 2 batteries, then 60 amps would be well within the limits, and not fry my alternator.

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[John61CT]

Go as high as you like, rather as high as your wiring is robust.

Good idea to use an infrared temp gun to look for resistance hot spots.

Batt vendors lawyers get more sway than the engineers, any LFP can go way over 1C no problem.

Of course their internal BMS may trip (or fry) if they didn't make it robust enough.

So maybe keep it at 100A max for two



So it takes 90 min to replenish rather than 45. . .

 

[John61CT]

If you were referring to the CL ACR, remember that won't reduce the voltage, just a pass-through, every charge source will need to be adjustable, gets expensive.

My reco is still the Sterling B2B

 

[hausmutti]

I have a small van.  It's a 1999 Ford Windstar mini van.  I have a 100 watt solar panel.  I replaced the starter battery with a 75 amp hour deep cycle trolling motor battery.  I got the biggest battery that would fit in the original location.  It is a cheap flooded battery.  Under the hood there is no venting problem and it doesn't take up any space inside.

How do you make sure you always have enough charge to start the van?

 

[Almost There]

Hausmutti  - sometimes it's just by trial and error.

For example, before I had my full electrical system up and running, I charged my kindle, laptop and cell phone off the starter battery. I found out that I could do that for 3 days while parked without a starting problem. Day 4 and I needed a boost.

During that time I used a rechargeable lantern and my headlamp for lighting in the van. Primitive but it worked.

If you're running light electronics off of your starting battery I really recommend getting a jump pack so that you can self-boost if necessary. Of course that also means figuring out a way to keep that jump pack charged.