Lithium battery charging in FW of truck

[Slownsy]

Can someone please explain. 2015 F350 alternator 200-220A, wire to rear of truck not clear on gage but about 20’, wire from plug to FW batteries 15’ or more supposedly protected by 30A fuse. I se people say batteries can draw power and fry alternator, and are installing dc to dc charger in FW to limit the charging. Also people are installing dc to dc chargers because of voltage drop in wire and smart alternators not supplying sufficiently. So how is all this happening,or is it. Please be gentle as I am no electric genus.
Thanks Frank.

[Slownsy]

BFL13 That is the one, yes I was aware of the 25V max on solar but frizzing weather is not usual around here, we are heading north to avoid it. Will report on how it is going after a bit of use, at the moment I have everything shut of as my new lithium batteries are at 96%.
Frank.

[BFL13]

The solar part of that charger only has 25V (Voc at 25C) limit, so can only be used with 12v panels in parallel and when not so cold that Voc gets too high.

OP has 150w 12v panels with 22.5v Voc, so it can work that way if not too cold.

Otherwise, the solar part of the charger could be by-passed using another controller going direct to battery and they could add their amps if set to the same voltage.

Perhaps it might be advantageous to split the solar array (OP has four 150w) so some goes to the Renogy at 12v and some goes to its own 24v controller with that part of the array in series.

It says the solar can maintain the engine battery if the house batts are full, but also says the DC-DC isolates the engine batt from the house batts. I haven't got to where it explains (if it does) how that can be.

"NEVER connect the solar panel to the charger without a service battery connection. The Battery must be connected first"

[BFL13]

Assume you got one of these. Was not aware of this product. Interesting!

https://ca.renogy.com/renogy-50a-dc-dc-on-board-battery-charger-with-mppt/

Please share any "lessons learned" from the trip.

[Slownsy]

Finished installation of new dc dc MPPT solar charger, so far so good, not much sun but rain at the moment but the dc dc supplied the 25A ok when I connected to truck, If I turn of the solar shut get the full 50A. So happy so far. Going on a 3 month trip in a week so will get a work out then.
Frank.

[BFL13]

Confusing. If that is a solar controller, it is buck only, while the actual DC-DC charger is buck/boost, which maintains the output voltage no matter what the input voltage is.

[Slownsy]

I today ordered a Renogy 50A dc dc MPPT charger, which I will connect to the 00 cable on rear of truck with 4 avg to charger, hopefully filling 2 golds with one.
Frank.

[pianotuna]

Frank,

Start an email with the makers to get the information you need?

[Slownsy]

That may be a problem Mexicowanderer, I am in Australia and dealer in America. Today I attached truck to FW truck charging at it usually 14.1 14.2V batteries in FW At 91% according to the TM, 9%of 300A = 27A used, put my clamp on at charge wire in FW and only showing 2.5A going in . I will check again when batteries are discharged further and be careful, while residing whether to get a dc to dc charger.
Thanks everyone for contributing.
Frank.

[MEXICOWANDERER]

Go to your new vehicle dealer
Seek Technical Service Bulletins regarding the factory interfacing of the alternators versus the ECU computer. You want to avoid accidental coding of charging system errors due to auxiliary battery charging errors.

[BFL13]

Voltage drop goes with the amps. More amps , more drop. 7-pin is low amps so not much drop. The lower voltage comes when the alternator regulator reduces its voltage once the starting batt is recharged.

IMO wait for more info to decide what to do if you still want any alternator charging, as there is conflicting advice on that.

[Slownsy]

The only reason for charging of truck would be if solar not doing its job, like heavy cloud or bucketing down. Only worried about smoking alternator. Also has my Honda generator which will put in 100A via my inverter charger if getting low. I am surprised finding 14.1V at batteries in trucks and also at FW with all the so-called voltage drop in wires.
Frank.

[BFL13]

With solar at say 14.5v and alternator charging at say 14.1, you will not get the total amps. You will get all the solar amps, but only some of what the alternator amps would be by themselves without the solar.

These are not real numbers, but just examples: Solar alone 20 amps, alt alone 10 amps, together 25 amps.

A DC-DC can be set to the same voltage as the solar, so they would add their amps for the total of what each could do by itself.

This does not answer the OP's question re the LFP draw with just the 7-pin, but he did say he wants to have both solar and alt charging. So you get more amps with the DC-DC, plus it isolates the LFP house batts from the alternator/starting batt, which solves that too.

If the OP does not want a DC-DC, then knowing his 7-pin amps (already lame) will be even less with the solar on, he might as well pull that 7-pin 12v fuse and just use the solar. Solves any LFP draw issue if there really is one.

Need to resolve is what amps the alternator can run continuously, and what wiring/fuse is needed. Mex seems to say the OP's alternator can't take even the 1/3 amps like PT said. That needs to be cleared up.

[FWC]

One thing to realize here is that almost all modern (as in > 2010 or so) alternators are 'smart'. They have a small microcontroller in them and communicate with the vehicles ECU, which can command the voltage output of the alternator and query the status of the alternator. As part of this system there is thermal monitoring of the alternator - it is gets too hot, it will sense this and drop the output voltage and thus the current to reduce the load on the alternator. In this case it is actually worse for the alternator to be connected to a DC-DC charger as opposed to directly to a battery. A DC-DC charger will actually draw MORE current as the alternator output voltage drops.

[FWC]

Slownsy wrote:
The trailer charging fuse in truck is 40A, in FW wire is 10 avg to a 30A fuse before batteries, the V from truck to FW is 14.1V to the 30A fuse before the batteries. ? Any way that batteries can damage the alternator,or will the fuse blow if to much amp are getting called for by batteries.
I can easily pull the 30A fuse in FW if necessary.
Thanks Frank

There is no way you will damage your alternator with this configuration and it is extremely unlikely you will pop the fuse either. You will likely find that you are not getting a whole lot of charge current to the battery though, which could be the motivation for a DC-DC charger.