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#1 Atlin

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Posted 20 November 2019 - 01:58 AM

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.


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#2 DanoT

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Posted 20 November 2019 - 05:07 AM

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.


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#3 Taku

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Posted 20 November 2019 - 12:28 PM

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.


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#4 ntsqd

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Posted 20 November 2019 - 01:42 PM

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.


Edited by ntsqd, 20 November 2019 - 01:44 PM.

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#5 Vic Harder

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Posted 20 November 2019 - 05:59 PM

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?


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#6 klahanie

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Posted 20 November 2019 - 07:35 PM

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.


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#7 Atlin

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Posted 21 November 2019 - 01:23 AM

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!).


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#8 craig333

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Posted 21 November 2019 - 01:53 AM

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. 


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#9 Vic Harder

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Posted 21 November 2019 - 03:14 AM

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   :D

 

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.


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2006 Silverado 3500 ext cab 8' bed LBZ

2012 ATC Puma Shell build - https://www.wanderth...012-puma-build/

Power considerations thread - https://www.wanderth...e-power-scotty/

 


#10 ntsqd

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Posted 21 November 2019 - 02:00 PM

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.


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