Supporting both Li and FLAs from one charger

[DavidM]

I have a good friend who just bought an older trawler, but with fairly modern electrics. It has a 60A PronauticP 60A charger with three battery outputs, each connected to house, propulsion engine starting and genset starting batteries. It has a setting for Lithium batteries but since all the batteries are currently FLAs it is set to that type.

He wants to change the house bank to 300 Ahrs of Lithiums.

If he changes the charger setting to Lithiums, will that harm the FLAs? If he leaves it set to FLAs, how will that affect charging the Li bank?

David

 

[Don L]

I wouldn't harm the FLAs. LFPs charge to 14.4v (assuming a 12v) and that is almost the same as the 14.6V of a FLA and the FLA start battery barely gets used.

I have a SLA start battery and it has been seeing LFPs voltages almost a year and it seems just right.

 

[Jeff F]

I don't disagree with Don L, but I wouldn't do it. For most situations the start batteries are charged by their engines, and survive just fine without a constant charge, just like a car battery.

If there is a need, a dedicated 15a charger matched to the LA bank will take good care of it, and should be an easy install. It can be AC or DC powered.

The bigger question is how charging under engine will happen. That may influence overall charging topography.

 

[tiltrider1]

If set to LFP I think everything would be fine. My concern is with the float side. I would check fluid levels in the start battery every 3 months.

I do wonder, is it better for the start battery to only see the alternator and risk going flat or is better to be tied in to a charger with the potential of boiling all the water out of the battery?

I have gone a different direction, I use a DC to DC charger from the house to the start battery.

 

[twistedtree]

I think you need to look at the specific voltages for the LFP settings to see how they match up with what the LFP batteries require, and what the LA batteries require.


And as mentioned earlier, you (he) will need to also check the charging voltages for any alternators, Inverters, etc.


Don L mentions charging LFP to 14.4. I have no doubt that some battery manufacturer's call for that, probably to trigger their balancers. For the battery cells themselves. 14.4V is right at the top end of what's acceptable. Where balancers can handle it, 13.8V to 14.0V is preferred by a lot of people.


Bottom line is that I think you need to go through the specifics of the batteries and chargers, and not rely on generalized answers.

 

[mvweebles]

As an example: According to OEM, my Lion Energy LFPs are happiest at 13.9v which is indeed lower then I've read for other batteries. These are a few years old now so who knows what current specs are.

Peter

 

[Don L]

Don L mentions charging LFP to 14.4. I have no doubt that some battery manufacturer's call for that, probably to trigger their balancers. .

the spec for mine are 14.4 +/- 0.2

I think anything near 14 is fine for a start FLA battery and I think the LFP balancing thing is worried about too much.

I am no expert. I try for be practical and to me batteries are consumables

 

[Jeff F]

I am no expert. I try for be practical and to me batteries are consumables

I agree they're consumables. But if the hype around modern smart chargers is to be believed they will extend the life of any battery over using a less well regulated charging source.

I dunno, maybe it's hype. But I worry less about battery health and longevity when the bank has its own dedicated charger, and in practice small dc-dc chargers work well in this application.

 

[Don L]

Smart chargers are not smart at all.

Everyone needs to decide how to manage their batteries. I truly am trying to pay less attention to them.

 

[Seevee]

Smart chargers (the regulator part) or a dedicated external regulator ARE SMART, but you need to program them to the specs needed for your batteries.


And, yes, using them will extend the life of your battery.



I've had good luck with them, poor without. Mostly AGM batteries.

 

[psneeld]

If the start battery is being fed by the motor most of the time and the charger is a bit high for the lead acid chemistry, how about an old school diode in the battery charge line to drop the voltage a bit to the start battery if really concerned?

 

[Don L]

Smart chargers (the regulator part) or a dedicated external regulator ARE SMART, but you need to program them to the specs needed for your batteries.

You think they are "smart"? I think they are stupid and all it is is 2 setpoints and a timer. Mine has 8 different sets of that. The only thing over old days chargers is time and float setting.

My "smart" charger NEVER got my acid batteries fully charged.

Meanwhile my solar controller isn't very smart, but it allows me to set the voltages, time, and min currents before dropping into float at least.

 

[DavidM]

If the start battery is being fed by the motor most of the time and the charger is a bit high for the lead acid chemistry, how about an old school diode in the battery charge line to drop the voltage a bit to the start battery if really concerned?

Not a bad idea at all. Will give it a try. Would need a 50A rated diode since the starting battery will be connected through the diode to a 40A charger.

David

 

[twistedtree]

Not a bad idea at all. Will give it a try. Would need a 50A rated diode since the starting battery will be connected through the diode to a 40A charger.

David

Just keep in mind that you need a 30 watt diode, which likely means one attached to a big heat sink. It will get very hot.

 

[DavidM]

Just keep in mind that you need a 30 watt diode, which likely means one attached to a big heat sink. It will get very hot.

Correct. Assuming a nominal 1 volt drop across the diode, at the full charger output of 40A, that results in a power/heat dissipation of 40 watts. Definitely not trivial.

David

 

[jleonard]

That heat might help keep the bilge dry.

 

[Packer fan]

One of the main reasons not to use a modern smart charger on Lion that isn't made for Lion is because it may spike the voltage once in a while to clean the plates. With Lion you do not want that spike.

 

[Don L]

well that wouldn't be a "smart" or modern charger

I have never seen a charging source be able to spike or raise a battery voltage beyond what the battery will allow for it's condition. I can set my battery charger to a 13.8V gel setting or a 15.0 FLA equalize setting and then turn it on. My LFP batteries will have the same voltage when I turn on the charger.

I was looking at a manual that showed the difference between a FLA and LFP charging profile. All that was different was the amp taper that occurs due to the FLA internal resistance. The charger did nothing different!

 

[Packer fan]

Take a look at this.
Desulfator chargers do spike the voltage. I would hope that your charger does this to your lead acid batteries or you are not getting the full life potential.

https://carbatterygeek.co.uk/battery-reconditioning-desulfation-conditioner-charger-desulfator-car/

 

[BruceK]

Equalization/Desulfation uses a voltage of around 16 volts in a 12v battery. Also involves "pulsing" to coerce the sulfur off the plates.
My previous boat had an Equalization program in the Solar Controller. Toggled on, it equalized once a month. With FLAs,you could tell it had run by a drop in electrolyte levels and a need to add water.

 

[Don L]

I am NOT an expert

But it gets old to battle with those that think they are and use true, but extreme stuff to prove it

hey this post turned me into a "guru" PROVING I am not an expert