yet another house battery charging question

[Peter_n_Margaret]

Short heavy cable = direct alternator charging is fastest and cheapest.
Longer smaller cable with voltage drop = DC-DC.
In between, heavier cable will give good results at a reasonable cost.
If you also have solar then the direct alternator does not need to provide 100% charge as the solar will finish it off, but it will give effective bulk charging faster than most other options.
And there is no problem providing multiple charge sources at the same time. Each will do what it does best. It is not necessary to choose only one.
Cheers,
Peter
OKA196 motorhome

 

[highwest]

I appreciate insight from everyone, very educational to see the philosophies behind the recommendations. I’m also not the OP, so sorry for the thread jack, but maybe it was helpful?

 

[Buffalobillcody]

alternators generally dont put out high output for long periods of time. Is there some pre-mature wear and tear coming from running heavy gauge wires? also, isnt it understood that charging two different types and state of charge batteries at the same time causes premature failure of the batteries? im in the same boat trying to upgrade my trailer set up, and am trying to decide between dc-dc and big heavy cables

 

[john61ct]

alternators generally dont put out high output for long periods of time.

Over generalizing. Depending on the vehicle 200+A actual output 24*7 is doable, even higher if you want. Precise VRs with adjustable setpoints, absorb+float stage, current limiting, separate voltage & temp sensing wires etc.

Of course a big investment.

> Is there some pre-mature wear and tear coming from running heavy gauge wires?

Huh? Not sure what you mean? but no. . .

> also, isnt it understood that charging two different types and state of charge batteries at the same time causes premature failure of the batteries?

That's what DCDC Chargers are for. But not always needed, set the alt to coddle House, Starters are usually cheap & robust coddling them usually not worth the cost.

 

[Buffalobillcody]

Over generalizing. Depending on the vehicle 200+A actual output 24*7 is doable, even higher if you want. Precise VRs with adjustable setpoints, absorb+float stage, current limiting, separate voltage & temp sensing wires etc.

Of course a big investment.

> Is there some pre-mature wear and tear coming from running heavy gauge wires?

Huh? Not sure what you mean? but no. . .

> also, isnt it understood that charging two different types and state of charge batteries at the same time causes premature failure of the batteries?

That's what DCDC Chargers are for. But not always needed, set the alt to coddle House, Starters are usually cheap & robust coddling them usually not worth the cost.

by wear and tear i was referring to the alternator, or other electrical components on the tow vehicle from having it put out a higher output for longer than normal operation while charging the house battery

is it harder on the start battery or house battery if you were to run a 2awg wire from the start battery to house battery for charging purposes? ive seen that suggested as a cheap efficient way to charge house batteries. To me vehicle reliability is more important than charge rates, thats what i was asking.
like you said, i think this might be the purpose of the dc-dc chargers.

 

[DaveInDenver]

by wear and tear i was referring to the alternator, or other electrical components on the tow vehicle from having it put out a higher output for longer than normal operation while charging the house battery

is it harder on the start battery or house battery if you were to run a 2awg wire from the start battery to house battery for charging purposes? ive seen that suggested as a cheap efficient way to charge house batteries. To me vehicle reliability is more important than charge rates, thats what i was asking.
like you said, i think this might be the purpose of the dc-dc chargers.

The most wear and tear on an alternator is having it spinning and that's regardless of the load. Usually bearings and brushes go bad before anything else. They can fail from fatigue in the windings or terminals but that's also more mechanical, vibration mainly. Heat isn't good for winding insulation, bearings, etc. But just being under the hood on the side of the engine in the presence of moisture and dust is doing more damage than anything. I mean, being a foot from 800°F exhaust manifolds and driving around in 100°F summers is going to be harder on it than an extra few degrees temperature rise from occasionally asking it to charge a second battery.

 

[john61ct]

It is the battery the determines how many amps it pulls, or tries to pull - chemistry determines CAR as a C-rate, proportional to Ah capacity, and of course a bigger bank pulls more amps.

That is without a DCDC charger limiting the current, which is why super-high CAR lithium batts really require them to protect the alt.

A fat wire gauge is to minimize **voltage** drop which is the other most common rationale for a DCDC.

Most modern alts to have overtemp protection, but voltage drops, in effect just stop charging. Hence why a DCDC can speed up the battery charging, even though in theory lower amp throughput.

is it harder on the start battery or house battery if you were to run a 2awg wire from the start battery to house battery for charging purposes? ive seen that suggested as a cheap efficient way to charge house batteries.

Nothing to do with the Starter batt, the current flows direct from the alt to House.

If no DCDC then a solenoid or ACR is required to stop House **loads** from pulling Starter SoC down.

The gauge of the wiring affects the effectiveness of the charge profile for House bank.

No impact on vehicle reliability.

DCDCs definitely helps with multiple factors.

But there are scenarios where they are not strictly required.

Of course you should measure amps & volts at all points, and monitor alt temperatures to ensure everything is working OK.

 

[john61ct]

The most wear and tear on an alternator is having it spinning and that's regardless of the load

A battery bank pulling hundreds of amps can literally burn up an alt without overtemp protection in a very short period of time.

Even a small LFP bank can do that, but some AGM can pull 0.8C, so a 300Ah bank can get up well over 200A.

 

[Buffalobillcody]

A battery bank pulling hundreds of amps can literally burn up an alt without overtemp protection in a very short period of time.

Even a small LFP bank can do that, but some AGM can pull 0.8C, so a 300Ah bank can get up well over 200A.

that was what i was expecting to hear. being off in the middle of nowhere with a dead house battery is alot less of a problem than a tow vehicle without a working alternator. i think for me personally, with my smaller electrical needs, will stick to a small charge coming into the 7 pin, and some solar.

 

[john61ct]

All the info you need to prevent any such problem is readily available here.

And is not a possible problem in the first place with a small lead bank, even just 200Ah.

 

[DaveInDenver]

A battery bank pulling hundreds of amps can literally burn up an alt without overtemp protection in a very short period of time.

Even a small LFP bank can do that, but some AGM can pull 0.8C, so a 300Ah bank can get up well over 200A.

He's not trying to charge a locomotive bank, just hanging a typically sized house battery. Two house batteries is maybe pushing it, but I think it's no worse than using a winch. It's not going to sustain hundreds of amps indefinitely. It's a heavy duty alternator doing heavy duty.

 

[john61ct]

I don't know what "typical" size means, each rig has its needs.

300-800Ah I call medium. . .

In any case best to give the info that covers the various alternatives, even edge cases, so the principles are understood.

 

[broncobowsher]

Wow, lots of discussion. An ignition powered relay, 12 gauge wire, 20A self resetting circuit breaker. It's really simple, it really works, it's safe and effective.
The wire has a voltage drop on a large load, correct and good. This will self regulate the charge rate. Extreme cases the circuit breaker will cycle. When the voltages are close there isn't much room for a voltage drop in the wire. If you have the alternator putting out 14V and the house battery is at 12V, there is only a 2V difference. The self regulating ability of a simple piece of wire will take car of that. It will eventually bring both batteries up to a full charge.

Now if the money tree is making more fruit than you know what to do with, there are a lot of different ways you can blow money on. Lots of theoretically perfect ways of doing it. You don't need perfect, you just need safe and effective. Which also happens to be way more cost effective as well.

 

[john61ct]

Sure that's fine if you're driving for 7+ hours, or have enough solar.

But if the goal is to get your House bank as much energy as quickly as possible from shorter drives, off grid for days or weeks, solar is not enough, no genset

then you need more than that.