How to make a cheap isolated dual-battery setup for $50

[dlichterman]

Can you please post some details/pics on both of these?
I would really like a time-delay on the solenoid so it doesn't start charging the 2nd battery until the engine has warmed up.

Thanks,
-Dan

Dan - I added a time delay to my setup. The part I found is "821TD10H-UNI" and can be found here: http://www.zorotools.com/g/00062834/k-821TD10H-UNI/

There were other (chinese cheap knockoff) options but I went with a well tested part as I don't want my truck to burn down. The timer is adjustable - you can find the datasheet here with all the options: http://www.alliedelec.com/images/products/datasheets/bm/MAGNECRAFT/70185027.pdf

-Another Dan

 

[Kevin.Hutch]

Solar Panel Fuses

Is there supposed to be a fuse in that solar stuff somewhere?

You have been drinking too much, the wires connecting your solar panel should be large enough to stand the maximum current of the solar panel so no fuse is required.

Kevin H

 

[crismateski]

You have been drinking too much, the wires connecting your solar panel should be large enough to stand the maximum current of the solar panel so no fuse is required.

Kevin H

wire size does nothing to protect the system in a dead short. fuses are inexpensive insurance.

 

[4RunAmok]

wire size does nothing to protect the system in a dead short. fuses are inexpensive insurance.

Wise words, Cris.

Pinch a wire between your battery and solar controller/panels, and see what happens. Have a fire extinguisher handy.

 

[Kevin.Hutch]

PV Fuses !!!

wire size does nothing to protect the system in a dead short. fuses are inexpensive insurance.

It is not a question of cost, just what are you protecting. Fuses are to protect the wiring.

The unique thing about PV panels is that they accept their maximum load without failing.


If I have a solar panel and I place a dead short via a fuse, the fuse will only blow if it is lower than the maximum capacity of the panel.


Now if the wire does not carry the maximum current the panel is capable of, then it is too small so what am I insuring against.


If I have a panel capable of 10 amps and I want to install a fuse, just what size fuse would you suggest is required a 10 amp will never blow.


Kevin H.

 

[86tuning]

But what if the wire is pinched to short- circuit? Wouldn't the battery feed power back up and create a fire hazard? Or am I missing something here?

 

[4RunAmok]

But what if the wire is pinched to short- circuit? Wouldn't the battery feed power back up and create a fire hazard? Or am I missing something here?

Yup, and THIS is what Kevin Hutch is not understanding.

If you leave fusing out of the line from the battery to the solar system, and something happens on that line, there is nothing to stop the battery from shorting out the line.

I have witnessed this first hand. The Engel solar panel system does not provide fusing at the clips that hook up to the battery, and when the wire shorted, it almost lit an entire flippac and contents ablaze.


But hey, by all means, take whatever risks you want, regardless of warnings you receive.

 

[graynomad]

Not sure if this has been mentioned, but as mentioned the fuse is to protect against the battery not the panel, as such it should be mounted at the battery end of the wires.

 

[4RunAmok]

Not sure if this has been mentioned, but as mentioned the fuse is to protect against the battery not the panel, as such it should be mounted at the battery end of the wires.

Did I not mention that? Forgive me if not.

Generally you want to fuse ANYTHING you hook up to a battery within 18 inches of the battery.

Or in my case, a 75 amp breaker at the battery, a 4 gauge wire from that breaker to a Blue Sea fuse block (rated at 75 amp max capacity). My solar controller outputs are connected to the Blue Sea fuse block with a 10 amp fuse in that slot.

 

[Seeker]

Ignorant question... Is there any potential for damage if you were to short the wire, blow the fuse, but the panel were still grounded due to the short? At that point you're pumping the panels full output direct to ground... I can't imagine that would be good for the battery over time.

 

[graynomad]

I don't think that would matter, the current from the panel will have a return path back to the panel, the battery would be none the wiser.

 

[4RunAmok]

Solar panels aren't affected by shorting, they are capable of handling the amount of current they produce.

 

[4RunAmok]

That looks more like a fuseable link. Meant for going from the battery post w/fuseable link, directly to a full size fuse block, from there you would distribute power to your electronics/accessories.

I just use a 75 Amp breaker directly off the battery leading to a Blue Sea fuse block, since the typical Blue Sea fuse block is rated to 75 Amps. If I have two fuse blocks, then I end up with two breakers and a line running to each fuse block, there is no need for a fuse between the breaker and the battery if the breaker is close enough to the battery that I would never worry about the wire in between shorting out.

 

[Kevin.Hutch]

Solar panel fuses

You have been drinking too much, the wires connecting your solar panel should be large enough to stand the maximum current of the solar panel so no fuse is required.

Kevin H

The statement related directly to solar panel fusing and I in now way dispute that as a matter of course every power "source cable" should be appropriately protected.


The key with a PV panel is that the cable should be capable of carrying the maximum current of the panel, hence it is protected from overloads from that source by the cables size.


The battery on the other hand will be capable of very high currents and unless high current loads are expected the cable can be down sized to better suit the load and as such needs protecting from the power available from the battery.


Thus large starter (100s of amps) cables are protected with high current fusible links or sometimes if the run is minimal and isolated,no protection at all, everything else should be fuse protected.

Kevin H

 

[Kevin.Hutch]

It is not a question of cost, just what are you protecting. Fuses are to protect the wiring.

The unique thing about PV panels is that they accept their maximum load without failing.


If I have a solar panel and I place a dead short via a fuse, the fuse will only blow if it is lower than the maximum capacity of the panel.


Now if the wire does not carry the maximum current the panel is capable of, then it is too small so what am I insuring against.


If I have a panel capable of 10 amps and I want to install a fuse, just what size fuse would you suggest is required a 10 amp will never blow.


Kevin H.

I don't see how I could be more specific, the wiring from a power source needs protection if one is to protect against an electrical fire.

There are two ways of Providing that protection,

1. Create a weak point in a known location ie fuse or circuit breaker of a value just below the wires current capacity or a location that a burnt wire will not be a major issue (as in the case of a starter cable).

2. Provide a circuit capable of handling the maximum the power source is capable of supplying.

Protect the wires to the generator/alternator/battery with a fuse/circuit breaker as close as practical to the source, but make solar panel the wires capable of handling the maximum short circuit load capacity of the solar panel/array.

Ie no fuse although an isolation switch would be wise.

Kevin h