Battery charging question

[Atlin]

So, as background, I have an F150 with no "smart alternator" and an ATC. I have an electrical problem. Twice now, I have run the house battery down to about 55% charge. When I fire up the truck, expecting the alternator to charge my battery, I end up finding that the 30A fuse between the starter battery and the house battery is blown. Obviously (to my mind anyway) this means that the alternator is trying to pump too much current into charging the house battery, thereby blowing the fuse. My question is what to do about this issue, other than keeping my house battery charged better? I do have an isolator between the fuse and the house battery, but no other things.

Thanks for any help/insight anyone can provide.

 

[DanoT]

Using a thicker gauge wire between starting and house batteries might help. I installed 6 gauge with a big fuse and a manual disconnect switch and it made a difference with a Phoenix camper vs stock wiring.

 

[Taku]

We have on 05 Tundra with an ATC. Have run the single battery down several times (due to lack of driving and/or just needing a new battery after years of use) - but have never had a problem with any blown fuses. I can't remember the gauge wire run from the truck to the camper, but I suspect it might the problem too.

 

[ntsqd]

There are lots of threads here on this very topic and there is a LOT that can be learned from them. The general take-away is that a single 10 ga. wire (most common camper OEM charge wire) is not nearly large enough. You need to consider the ground as well, it is part of the circuit and a circuitous ground path does not work well.

The key is to look at the 3% voltage drop at the max expected charge rate over the entire circuit length (ground path included). I looked into batteries just a little and concluded that 80A was about the upper limit that I could expect. Like DanoT I ran a 6 ga. power wire and a 6 ga. ground wire directly from one truck battery to the camper battery, with an 80 amp manual 285 Series breaker at both ends. Manual breakers are more expensive than fuses, but they also allow me to easily de-energize the circuit to work on it. There's a battery at both ends so there needs to be protection at both ends.I used a BEP Marine VSR (Voltage Sensing Relay) for connection/isolation, but there are other options that may have more appeal.

I got all of that done and then added solar. I should have done that first. There are a lot of threads here on that topic too. Both of these related topics have their own rabbit holes. Mention of the Handy Bob blog will shortly rear itself. Suggest going and reading that first. Then read the posts that agree and disagree with him. His point of view is a bit extreme for most of us, but what he says is correct. Even if he is more than a bit repetitive.

 

[Vic Harder]

So, as background, I have an F150 with no "smart alternator" and an ATC. I have an electrical problem. Twice now, I have run the house battery down to about 55% charge. When I fire up the truck, expecting the alternator to charge my battery, I end up finding that the 30A fuse between the starter battery and the house battery is blown. Obviously (to my mind anyway) this means that the alternator is trying to pump too much current into charging the house battery, thereby blowing the fuse. My question is what to do about this issue, other than keeping my house battery charged better? I do have an isolator between the fuse and the house battery, but no other things.

Thanks for any help/insight anyone can provide.

Atlin, I'm not sure anyone has addressed your specific issue yet... blowing fuses. Adding thicker wire would allow for more current (which is generally good) but would only make it more likely that you would blow the existing (too small?) fuse.

I'd be tempted to replace the fuse with a breaker, and to pay more attention to the battery's SOC with a good monitor.

AND we need to figure out what happens first... fuse blown and then battery slowly degenerates, or battery SOC gets so low that the inrush current overwhelms the fuse.

Q: If the fuse is blown, and you replace it.... does it blow again? Or do you avoid that by using a AC powered battery charger?

 

[klahanie]

I end up finding that the 30A fuse between the starter battery and the house battery is blown
....
I do have an isolator between the fuse and the house battery, but no other things.

Is there a fuse between the house battery and the camper distribution panel/fuse box. Or does the distribution panel have a large main fuse ? Seem me this would be the circuit with the 30A fuse. Was your install a factory hook up ?

I'm thinking to agree that inrush current to the low house battery is blowing the fuse now. Fusing this circuit protects the wiring. Larger gauge wire would allow a higher rated fuse. It also might protect the house battery but then again, jumper cables aren't normally fused but fuse protecting the wiring is a good idea against shorts if the wire gets damaged etc.

 

[Atlin]

Thanks for the input. I realize I could upsize the wires and fuse but that seems to not really address some fundamental problem. Surely not everyone has #4 wire running to their campers.

To answer the questions, this was a standard install by ATC. I did add a Victron SOC monitor myself. This fuse blowing has happened twice now. On most of my trips, the battery SOC goes down to about 80% overnight and I have had no issues with the system getting recharged through the alternator the following day. However, a couple of times the SOC has gone much lower (probably ~60% or below), and the following day I discover that the battery has not charged while driving and the fuse is blown. Thus my thought that the alternator is trying to push too much current through the wires because there is insufficient back-resistance with the battery low (i.e., "inrush" current).

If the inrush current is the problem, would addition of a DC to DC charger provide sufficient back-resistance to keep the inrush down below the level of blowing a fuse? From what I can find on the internet, that seems to be a reasonable solution. And it would allow me to add solar panels at a later time.

FWIW, I called the local Ford dealer after posting this morning, and they seem to know nothing about "smart alternators" (even claimed they had never heard the term before, and this is a guy in the maintenance department). Looking online suggests (but nowhere could I confirm) that all these trucks now have smart alternators that ramp down current when the starter battery is charged up to about 80%. I'm thinking that whether or not I have a smart alternator, having a DC-to-DC brain box would help with keeping the camper battery topped up properly (particularly if it keeps the fuse from blowing!).

 

[craig333]

You probably need a better battery. If you go that low overnight its probably too small. What size is it? Is it a true deep cycle? Might be time to think about dual batteries if your usage is that high.

Btw, I ran 6ga wire in mine. I've blown a 50 amp fuse but I was going the other way, Using the camper batteries to charge the truck batteries.

 

[Vic Harder]

Thanks for the input. I realize I could upsize the wires and fuse but that seems to not really address some fundamental problem. Surely not everyone has #4 wire running to their campers.

To answer the questions, this was a standard install by ATC. I did add a Victron SOC monitor myself. This fuse blowing has happened twice now. On most of my trips, the battery SOC goes down to about 80% overnight and I have had no issues with the system getting recharged through the alternator the following day. However, a couple of times the SOC has gone much lower (probably ~60% or below), and the following day I discover that the battery has not charged while driving and the fuse is blown. Thus my thought that the alternator is trying to push too much current through the wires because there is insufficient back-resistance with the battery low (i.e., "inrush" current).

If the inrush current is the problem, would addition of a DC to DC charger provide sufficient back-resistance to keep the inrush down below the level of blowing a fuse? From what I can find on the internet, that seems to be a reasonable solution. And it would allow me to add solar panels at a later time.

FWIW, I called the local Ford dealer after posting this morning, and they seem to know nothing about "smart alternators" (even claimed they had never heard the term before, and this is a guy in the maintenance department). Looking online suggests (but nowhere could I confirm) that all these trucks now have smart alternators that ramp down current when the starter battery is charged up to about 80%. I'm thinking that whether or not I have a smart alternator, having a DC-to-DC brain box would help with keeping the camper battery topped up properly (particularly if it keeps the fuse from blowing!).

I don't have 4g... mine's 2g

Good that you have a Victron BMV.

Discovering that the fuse is blown... ideally, you would look at the Victron before you start the truck, and think "Hmmm, this might blow the fuse" and then watch the Victron as the truck is started... and note how much current is trying to flow to the camper battery.

Did you say how big the fuse is? Typical is 30A.

If the wiring is factory stock, it is likely 10g. If so, 30A is the right size fuse. Putting in a bigger fuse is not a good idea.

DC-DC charger. This would be placed close to the camper battery, and would STILL blow your fuse unless you buy one that is rated to only pull 30A or LESS That's not ideal. I have seen 80A on my system for 10-15 minutes, which does a LOT of bulk charging early on. nice.

By the way, DC-DC really helps folks who have smart alternators. You don't.

Running thicker wires might be the answer. Not only would it lower the voltage drop (not likely your problem), you could then safely put in bigger breakers.

 

[ntsqd]

The oft stated advantage of fuses over breakers is that they handle in-rush currents better. They are, by nature, a "slow-blow" design and can safely handle momentary over-currents without blowing. Breakers are not as good about that. My impression is that even the so-called "slo-blo" breakers are less tolerant than a fuse. I think replacing 30A fuses with 30A breakers will be an objection lesson in frustration.

Does the Victron data log? Would be nice to see what the current was when the fuse blew. Would also help in deciding if a wire gauge size upgrade is in your future. I think that it is, but we don't have any direct data, only incidental, to support that. FWIW mine are only 6 gauge wires, not 4 or 2 or even bigger. I got the raw wire (Carol welding cable actually), plated cable lugs, and adhesive lined heat-shrink all from the local Power-Stride battery store. The tandem cable that I used under the truck came from West Marine. I used it for it's extra, 'Romex'-like outer cover being another protective layer and being bundling together it made routing & support easier.

 

[Atlin]

OK, possibly problem solved. I was crawling about under the truck today to look closer at wiring, and moved the power wires a bit and ZAP - clearly a short, started the insulation on fire even. Pretty scary. Obviously blew the fuse, so it has been doing it's job. This also probably explains the intermittent nature of the problem. So, at the very least I'll be replacing some wires, and will put them in a plastic wire loom or something like that to protect them better. And I'll probably replace the battery with more capacity (wife just started using a CPAP, so that is an additional drain on the battery overnight).

Thanks to all for thoughts and suggestions. Will make for a better electrical system overall.

Cheers,
Atlin

 

[Vic Harder]

whew! Glad that the fuse was doing its job!

 

[Advmoto18]

Good to read you found the issue.

I've never been comfortable replacing blown fuses, resetting tripped breakers, unless I know exactly WHY they blew/tripped and make repair. Making assumptions can lead to disastrous consequences. Read about Air Canada 797 accident here. This accident changed world wide commercial airline policy/regulations on resetting tripped circuit breakers while airborne. Fortunately, if our truck/camper catches on fire, we can pullover and jump out.

I too went with 6 ga welding cable, tinned lugs and adhesive lined shrink wrap. All standard components from my days rigging saltwater fishing boats.

As Thom mentioned, many folks overlook the Ground and this is where I generally start looking with intermittent electrical issues.

 

[Casa Escarlata Robles Too]

I need a simple explanation.
The system.
ATC Bobcat, stock wiring,100A AGM battery,105W solar,
battery isolator, 150W inverter,Truckfridge,3 way fridge.

The problem.
While driving with the fridge in 12V mode ,even in great sun
on the solar,the isolator wants to cycle on/off.
Therefor not charging the camper battery while traveling down the road.

I have run the 3 way fridge (truck not running) with solar output at about 75%W
and 5.5 amps. I can keep this up for about a few hours before the battery voltage falls below 12v.

So I would think on sunny days while driving and fridge in 12v mode the truck alternator would charge
the camper battery and not cycle the isolator.
Any ideas.
Frank

 

[Vic Harder]

Frank, the problem as you describe it is that even when driving the camper battery doesn't really charge. This is a known issue with 3 way fridges. No such problem exists with 2 way fridges.

That said, you may also have a problem with the truck to camper wiring/separator. The cycling on/off is typical with the stock separator FWC used to use. I could explain, but that would deviate from your request to KISS.

Your options include:
1) New fridge
2) Replacing the separator with a Blue Sea 76xx series unit. The 7622 that I have allows me to force (dis)connection
3) Upgrade the wiring from truck to camper from (10g or 14g) to 4g or thicker.

Oh, no... wait. I see you have a Tundra. That's an issue too. They are one of the first units to have "smart" alternators. Your best bet is a DC-DC charger placed close to your camper batteries. It would replace your problematic separator and you can still use the wimpy stock wiring.

 

[MidAtlantic]

Oh, no... wait. I see you have a Tundra. That's an issue too. They are one of the first units to have "smart" alternators. Your best bet is a DC-DC charger placed close to your camper batteries. It would replace your problematic separator and you can still use the wimpy stock wiring.

https://www.ctek.com/uk/products/leisure-sport/d250sa

• No need to replace the wimpy wiring
• Replaces the cheap separator and controller
• Handles smart alternators and solar panel

 

[ntsqd]

Downside to the D250S is a max of 20A charge rate. I doubt that it has ever happened, but I'm set up for 80A. That wasn't the reason though, the reason was voltage drop. Granted, with a DC-DC converter voltage drop is not an issue. I'd be sold if it offered a 40A-50A charge rate.

 

[Casa Escarlata Robles Too]

Frank, the problem as you describe it is that even when driving the camper battery doesn't really charge. This is a known issue with 3 way fridges. No such problem exists with 2 way fridges.

That said, you may also have a problem with the truck to camper wiring/separator. The cycling on/off is typical with the stock separator FWC used to use. I could explain, but that would deviate from your request to KISS.

Your options include:
1) New fridge
2) Replacing the separator with a Blue Sea 76xx series unit. The 7622 that I have allows me to force (dis)connection
3) Upgrade the wiring from truck to camper from (10g or 14g) to 4g or thicker.

Oh, no... wait. I see you have a Tundra. That's an issue too. They are one of the first units to have "smart" alternators. Your best bet is a DC-DC charger placed close to your camper batteries. It would replace your problematic separator and you can still use the wimpy stock wiring.

Thanks Vic.My Tundra is an 2002,did they use a smart alternator in trucks that old?
I have a "isolator" not the stock separator which was recalled back in 2011.
ATC replaced the old with the new isolator.

I'll have to do more research on a DC/DC unit.
Thanks for the info.
Frank

 

[Vic Harder]

My Tundra is an 2002,did they use a smart alternator in trucks that old?

I'll have to do more research on a DC/DC unit.

I'm not sure when they started doing the smart alternators Frank.

I've had both the Renogy 30A and just now I am swapping out the Renogy and installing a Victron Orion 30A. Why switch? The Victron unit is much smaller, and I love the Bluetooth interface Victron uses. Plus, I think I can be called a Victron groupie now that I have 4 of their devices in my rig!

I'm with Thom, a 40A charge rate would be awesome, but I worry about the strain on the alternator.

My particular Victron Orion is giving me grief, so I've started the troubleshooting process. Stay tuned!

 

[Casa Escarlata Robles Too]

Vic this is my isolator.
The Surepower separator was recalled due to over heating.
This was the replacement from Marty.

Has worked great.I like it as both the camper and truck battery are kept charged up by
the solar system.And it doesn't get hot like the SurePower.

I've looked at the BlueSea ACR 7600 series ,is this what you are referring to?
From the description it sounds similar to what I have.

Thanks Frank

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