Battery Fuse for Solar/Charger System

westend wrote:

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That brings up another nasty secret about solar use: Once you get 200W, you start thinking what else would you like to do with free energy and upgrading comes into play. That may impact how you install everything and whether you want to upsize wire or get a bigger controller, initially.

Heh, what I really need is another battery bank for the solar panels I've already installed. Currently only 216Ah. But that could well require a heftier truck as my tongue weight has pretty much maxed out the truck's receiver hitch and rear axle now.

And then of course if we get a bigger truck, I'll probably "need" a bigger trailer, and a bigger solar system ...

Nah, not unless I win the lottery.

brulaz wrote:

Almot wrote:
On-battery fuse by Bluesea is the easiest and closest to battery. Not cheap. Check Amazon, I think I paid $25 for a single block and $18 for a fuse. You don't need a double block if this is only for a battery fuse.

Yes, that's what I linked to in the first post. So guess everybody has had a good experience with it. A bit expensive though ... the wiring, cables, breakers, breaker box, and fuses are getting to be as expensive as the solar panels.

EDIT: westend's solution is a lot cheaper though. But I can't find a 60A version. The 60A equivalents come as MIDI fuse which are smaller and use a fuse holder, not bolt on.

Yup, welcome to the wonderful world of solar installation where modules are dirt cheap but copper is over $3/lb. ;) At least you haven't priced marine disconnect switches......yet. :B

I buy a lot of DC stuff at Waytek Wire. They are close, have good inventory, are straight forward with customers, and don't have the lowest price. Customer service is good but they are geared towards installers and commercial enterprise. Ask them and they will send a catalog or two. They also have that same MIDI fuse in 60 amp flavor.

Be sure that you know what works for you with circuit protection and fusing. The ANL type of fuse has a much quicker time constant than a MIDI and there are others, slower still. For my application and needs, the MIDI fuses meet the requirements. I do have the wires that are pictured from my 6V bank housed in ABS pipe so it would take hitting a big rock and a perfect shear of the wires to blow the fuse.

Almot asked about the undersizing of the fuse: The wire that is terminated to the battery bank (pictured) is 1/0 welding cable. I am running a 1000W inverter for a fridge. Poppa don't like wasting a ma.

That brings up another nasty secret about solar use: Once you get 200W, you start thinking what else would you like to do with free energy and upgrading comes into play. That may impact how you install everything and whether you want to upsize wire or get a bigger controller, initially.

Almot wrote:

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Edit:
My bad. Voltage drop calculators are to be used with "one-way" distance. Yes, <2% drop with AWG 6.
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OK, that's a relief. Just checked the Rogue manual, and it also has a table that says you should be able to go 20' with 6ga at 12V and be under 2% voltage drop.

Yes, load cable is separate, and there is a voltage sense wire in Rogue, but you connect the loads wire in parallel to the controller wire. Usually - on the bus near controller. When controller is raising the voltage to compensate for drop, the load wire and all the appliances are getting this raised voltage - not the "correct" voltage that is on the battery terminals.

The only way to avoid mistreating your appliances while dealing with too high voltage drop is to connect the loads cable directly to the battery.

Edit:
My bad. Voltage drop calculators are to be used with "one-way" distance. Yes, <2% drop with AWG 6.

Now, with converter pumping 60A through the same cable - this is how I see it. Converter has no voltage sense, so there will be uncompensated drop and lower voltages on terminals. Your 12V devices are safe then, but charging will be under-volted. Though with converter it is always undervolted, with those long #8 wires from converter to battery. I wouldn't trust my WFCO with anything but floating charge.

Almot wrote:

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Rogue 3048 accepts max #4 wire, but in his case I would use #2. Or - a short run of #4 to the Pos bus near controller or to controller breaker, and then #2 to battery.

Rogue says to keep the voltage drop to less than 2%, but it also has voltage sense wires, that I intend to use.

Maybe I'm doing the calculations wrong. Rogue says #6 wire has a resistance of 0.00040 ohm/ft, so 20' (MAX) is 0.008 ohms. The MAX current I will get out of a 390W array via the Rogue is 27A at 14.4V, less if only 90% efficiency: say 25A. Then the Voltage drop is 25*0.008 = 0.20V, which is only 1.3% of 14.4V

Where am I going wrong on this?

Now the same cables will also be used for the PD9260 which can pump out up to 60A to a deeply discharged battery. So the voltage drop will be greater there, but I don't really care. We'll be on shore power then; there's no plans for a generator.

And these cables will not be used for any loads at all. Those are separate and remain what the trailer came with.

Almot wrote:
On-battery fuse by Bluesea is the easiest and closest to battery. Not cheap. Check Amazon, I think I paid $25 for a single block and $18 for a fuse. You don't need a double block if this is only for a battery fuse.

Yes, that's what I linked to in the first post. So guess everybody has had a good experience with it. A bit expensive though ... the wiring, cables, breakers, breaker box, and fuses are getting to be as expensive as the solar panels.

EDIT: westend's solution is a lot cheaper though. But I can't find a 60A version. The 60A equivalents come as MIDI fuse which are smaller and use a fuse holder, not bolt on.

150A is "undersized"? Must be some serious loads there. My guess - a microwave.

Rogue 3048 accepts max #4 wire, but in his case I would use #2. Or - a short run of #4 to the Pos bus near controller or to controller breaker, and then #2 to battery.

brulaz wrote:

westend wrote:
Best practices is to locate the fuse within 18" of the battery. I just bolted a fuse onto the (+) terminal of the battery and bolted the wire lug onto the fuse. I have the (+) battery wire supported so that there is no movement.

Curious: How far is the charge controller from the batteries?

Hmm, that sounds like a really good & cheap solution. What type of fuse can you bolt to the battery? Do you have a picture?

I'm estimating max 10' run there and 10' back, but I haven't placed the MPPT or run the cables yet, so could be less. With 6ga wire the Voltage drop should be <2% for the MPPT currents.

The PD9260 will use the same wires, and its current could be higher, up to 60A I guess; it will have more voltage drop then. Will want the fuse to be 60A for it.

I used this CB Mega fuse for my battery main fuse and have it somewhat undersized so that I'm sure it will interrupt should I have a short in the main wires. I have the converter, inverter, and charge controller fused separately in buss boxes.



Like others, I'd recommend the use of 4AWG instead of 6AWG. My take is that it makes no sense to give up power by trying to save a few bucks on wire. If the terminals on your charge controller only support the smaller 6 ga. terminals, there are aftermarket lugs that will mate to 4 ga. and have a smaller spade connector.

Right. Southwire calculator says drop <2% with wire #2 at 30A/20ft.

Yes, too high voltage of raised/compensated setpoints will affect other appliances unless the trailer load cable is connected directly to the battery.

brulaz wrote:

I'm estimating max 10' run there and 10' back, but I haven't placed the MPPT or run the cables yet, so could be less. With 6ga wire the Voltage drop should be <2% for the MPPT currents.

The PD9260 will use the same wires, and its current could be higher, up to 60A I guess; it will have more voltage drop then. Will want the fuse to be 60A for it.

IMO, You are selling yourself and your batts short if you are running 6 ga more than a foot or 2 from your controller. Same with the converter. You can't compensate too much with your voltage setpoints as you will impact other appliances so might as well conserve as much voltage as you can. Go big or go home as some would say and 6 ga ain't big. At least 4 ga would have advantages, 2 ga more so. YMMV.