Lithium batteries and alternator protection.

[N6WT]

The six 6 volt lead-acid house batteries in my class A DP have gone bad. I am looking to replace them with 6 Battleborn 100Ah 12v LiFePO batteries. Eventually I will be adding solar.

I am not looking for recommendations on what batteries and components to buy, I have made up my mind so please don't try and change it.

The reason for this post is, I am reading that in class A motorhome when you switch batteries you should install a DC to DC charger to protect the alternator of the motorhome from overheating. I would like to know if anyone here has done this to their motorhome, what did you use to do it and where inline did you install it?

[S_Davis]

theoldwizard1 wrote:

CA Traveler wrote:
Also 13.2V would not be a issue for me as it indicates a charged battery and the alternator is only supplying chassis and converter loads. A higher voltage indicates the chassis battery is drawing amps so at least the DC-DC converter has less conversion losses.

Almost all vehicles for the past 15-20 years or so, use some kind of a smart charging system. The voltage from the alternator is controlled by the engine computer and can vary over a wide range.

Not on 2009, 2013, 2019 GM 2500HD diesels, my last three trucks all have had steady voltage at about 14.2 no matter what. They must be in the almost none category.

One of my Redarc 50 amp chargers pulls 50 amps from the alternator and output is about 46 amps to the batteries, so on Redarc it looks like the rating is what is pulled from the alternator.

[theoldwizard1]

CA Traveler wrote:

theoldwizard1 wrote:

Almost all vehicles for the past 15-20 years or so, use some kind of a smart charging system. The voltage from the alternator is controlled by the engine computer and can vary over a wide range.

Does this apply to MH engines delivered w/o an alternator which is upgraded to a larger alternator due to the larger power demands? Is tbhere any additional information on this subject?

Smart charging started in cars but moved to all Ford produced vehicles fairly quickly. The size of the alternator did not matter.

What additional information do you want ? To see it in action, turn just the headlights on for about 5-10 minutes. Hook a multimeter directly to the battery. Start the MH and hold it at a high idle. The initial voltage will be in excess of 14V. It will drop within a few minutes. After about 5-10 minutes of high idle, the voltage will drop down to about 12.6V - 13.2V. This is lower than any conventional alternator/regulator.

[CA_Traveler]

theoldwizard1 wrote:

CA Traveler wrote:
Also 13.2V would not be a issue for me as it indicates a charged battery and the alternator is only supplying chassis and converter loads. A higher voltage indicates the chassis battery is drawing amps so at least the DC-DC converter has less conversion losses.

Almost all vehicles for the past 15-20 years or so, use some kind of a smart charging system. The voltage from the alternator is controlled by the engine computer and can vary over a wide range.

Does this apply to MH engines delivered w/o an alternator which is upgraded to a larger alternator due to the larger power demands? Is there any additional information on this subject?

[Tom_M1]

I have had my Renogy 170ah lithium battery for 2 years and have had no issues with it hooked directly to the alternator.

[theoldwizard1]

CA Traveler wrote:
Also 13.2V would not be a issue for me as it indicates a charged battery and the alternator is only supplying chassis and converter loads. A higher voltage indicates the chassis battery is drawing amps so at least the DC-DC converter has less conversion losses.

Almost all vehicles for the past 15-20 years or so, use some kind of a smart charging system. The voltage from the alternator is controlled by the engine computer and can vary over a wide range.

[CA_Traveler]

Also 13.2V would not be a issue for me as it indicates a charged battery and the alternator is only supplying chassis and converter loads. A higher voltage indicates the chassis battery is drawing amps so at least the DC-DC converter has less conversion losses. Normally the alternator has extra capacity. IF this causes a alternator issue then the installation etc was at fault and needs to be corrected.

[BFL13]

Tom/Barb wrote:
This is what we did, A 30amp DC to DC charger gives you the ability to charge the coach battery bank while running the coach engine.
This limits the engine alternator to 30 AMPs thus prevents overheating the engine alternator....

Do you still believe that ?
Hope the OP doesn't .

[CA_Traveler]

Probably best to check the specs/directions for whatever device you choose to get better information rather than some posts. The Victron has several models and connections types. It detects both battery voltages and uses algorithms that adjust to the battery voltages as the conditions change. IE not the voltage at the device but the voltage at the batteries. They recommend a 60A fuse for the 30A model for the purpose of protecting against a short. In general fuses are used to protect wiring and they are not current limiting devices as in 31A on the 30A output. And yes the Victron spec of 30A is for the output. It's interesting reading with more information. No question for me that it's well engineered.

[pianotuna]

N6WT wrote:
I would assume it is ok since they sell this:
https://battlebornbatteries.com/product/600ah-12v-lifepo4-heated-battery-kit-6-batteries/

Great.

Now wire in a balanced manner.

[theoldwizard1]

BFL13 wrote:
A 30A DC DC could pull 45 amps. Output is 30

On a travel trailer, that circuit usually has a 50A fuse. A modern alternator can handle it.

[N6WT]

pianotuna wrote:

N6WT wrote:
I am looking to replace them with 6 Battleborn 100Ah 12v LiFePO batteries. Eventually I will be adding solar.

I suggest checking with BB to find out if six may be placed in parallel.

Do make sure to wire them in a balanced manner.

I would assume it is ok since they sell this:
https://battlebornbatteries.com/product/600ah-12v-lifepo4-heated-battery-kit-6-batteries/

[pianotuna]

N6WT wrote:
I am looking to replace them with 6 Battleborn 100Ah 12v LiFePO batteries. Eventually I will be adding solar.

I suggest checking with BB to find out if six may be placed in parallel.

Do make sure to wire them in a balanced manner.

[otrfun]

Tom/Barb wrote:

BFL13 wrote:

Tom/Barb wrote:

BFL13 wrote:

If the DC-DC is charging the house batts with 30 amps at 14.2v , that is 426 watts output..

the fallacy of your theory is Alternators don't always operate at peek power/voltage/potential

The 30 Amp DCtoDC Charger is a limit, not a constant amperage.

We have had several threads about this. A recent one that might explain your set-up was that a "30A" DC-DC means output for a Renogy, but it could mean input for another brand.

In any case, input is higher in watts than output. If the input limit is 30A then at 13.2v that is 396 watts. Charger efficiency of 95% (being very generous) means output is 376 watts.

376/14.2 = 26.5 amps charging from the charger minus any wiring loss to the house batts for amps to the house batts

why would you mention Renogly when we are taking about Victron equipment?

DC to DC chargers won't charge to 30 amps at all times, they will vary the amperage rate to 0 amps when the battery is fully charged.
I believe my system will never show 30 amps, because we never have seen 30 AMP charge rate in 2 years even the batteries are low .

we left Quartzite Az after 2 days on batteries and our batteries were topped up in 3 hours with out exceeding 20 amp charge rate.

I only know what I see on our system, other manufacturers may differ so don't confuse the issue.

Our dc to dc charger is rated at 40a. Unless our lifepo4 cells are in the the last 5-10 min. of the charge cycle, it's always producing a constant, consistent 40a of charge current. We obtain 40a of charge current charging from 0 to near 100% SOC under all conditions. The converter in our camper, which is rated at 45a, operates just like our 40a dc to dc charger. Unless the lifepo4 is in the last 5-10 min. of the charge cycle, the converter is producing its rated 45a of charge current.

You appear to have a 30a dc to dc charger that produces no more than 20a of charge current. One has to wonder what the 30a rating is for.

When a charging device has a given current rating, most would expect it to provide that rated current in the form of actual charge current. When it doesn't, then a clarification or explanation of the rating would certainly be helpful.

[RLS7201]

N6WT wrote:

RLS7201 wrote:
I have yet to see a report of any one burning up their alternator while charging their Li batteries directly from the alternator.
Can some one show us an engineer's report at what % an alternator is designed to operate?

Richard

https://youtu.be/jgoIocPgOug

OK, good point but our alternators are used very little at idle. Most of the time our alternators are spinning at 6000 RPM or greater. 6000 RPM being the standards by how they are rated. Those doing the tests are NOT using the same alternators that we us in our RVs.

Richard

[BFL13]

https://www.victronenergy.com/upload/documents/Datasheet-Orion-Tr-Smart-DC-DC-chargers-non-isolated-...

This is the 30A unit they list. Is that the one you have?

Not sure what that non-isolation means. One of the reasons to use a DC-DC is for isolating. OP take note for operating with LFPs! (The Renogy ones do isolate, eg).

It says its output is 30A at 430w so voltage is 14.3. That is too low for many house battery specs, but would work with LFPs. (Renogy ones can do 14.7v for some profiles) A worry with LFP is the two-hour abs time, but it says you can change that time (20 minutes after reaching Vabs is about right).

It says it is 87% efficient, so at 430w out, that is 494w input. Pick a number for input volts. EG 14v would make that 35 amps draw at the charger end of the alternator/engine batt wires

IMO the OP might want to look at other models of DC-DC. Be good if others on here would comment on all this for their brands and specs.