Odd circuit breaker arrangement at battery

[Dave Marchetti]

Hi everyone.
I'm stumped as to why the previous owner had this breaker arrangement at the battery for the roofs power lift. I haven't changed it yet and we've been using the camper for three years now. Any guesses out there? Thanks in advance!

2008 Forest River Flagstaff MAC / LTD 205

Dave

[Twinboat]

That's not odd, it's a cheap way to double the amp capacity of one of those breakers.

[Bob K4TAX]

Sure, it doubles the amp capacity of the circuit. However, from the picture, it is not optimally wired. One connection should be on the top left terminal in the picture and the other wire should be on the bottom right terminal in the picture. This will equally share the current through the breakers. As it is shown the breaker on the left will carry the majority of the current in something like a 60-40 ratio.

Bob

[Twinboat]

Originally Posted by Bob K4TAX

Sure, it doubles the amp capacity of the circuit. However, from the picture, it is not optimally wired. One connection should be on the top left terminal in the picture and the other wire should be on the bottom right terminal in the picture. This will equally share the current through the breakers. As it is shown the breaker on the left will carry the majority of the current in something like a 60-40 ratio.

Bob

Why would that be ? The voltage drop of the 2, 1 inch long copper bars would be un-measurable with standard equipment available. It's been that way since 2008 and it still may be working.

This is a recreational vehicle, not a vehicle built for long term space travel. It's fine as built.

[chrisski]

Perhaps my computer screen is not working, but that looks like rusty brown iron busbars, not corroded green of copper.

As for the current not going through balanced, this link explains why this happens in batteries with resistance.
http://www.smartgauge.co.uk/batt_con.html

[Dave Marchetti]

A few points..
1. Maybe calling something "odd" is a matter of opinion, but why not just use one breaker?
2. I am the third owner so who knows if that is the original arrangement.
3. The bus bars appear to be brass.

Thanks

[Twinboat]

Originally Posted by chrisski

Perhaps my computer screen is not working, but that looks like rusty brown iron busbars, not corroded green of copper.

As for the current not going through balanced, this link explains why this happens in batteries with resistance.
SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

The Smartgauge site is using maximum amps thru minimal size cables to make a point. In real world battery wiring, the cables will be much larger, and the test results very different.

It's something how everybody references this one site, but never looks for any other site, to back up what it shows. I have looked and there are no others.

Like I said, a voltage drop calculator in that situation will show un-measurable drop.
A prime example is your house circuit breaker panel. Do the circuits on the bottom supply lower voltage then the top ones, closer to the main breaker ?

[5picker]

They likely could not find a 40a DC circuit breaker so they used two 20's.
Not all that uncommon in the DC world.

And I agree, having the wires attached as they are, is perfectly fine and no measurable difference could be made in the real world.

The same with the above reference of connecting two 12v batteries in parallel and the folks that say one lead MUST on the POS of one battery and one lead MUST be on the NEG of the 2nd battery.
I want someone to show me the voltage drop and resistance in a 6" piece of 2 AWG or 1/0 battery cable that connects the two.

[Bob K4TAX]

Originally Posted by Twinboat

Why would that be ? The voltage drop of the 2, 1 inch long copper bars would be un-measurable with standard equipment available. It's been that way since 2008 and it still may be working.

This is a recreational vehicle, not a vehicle built for long term space travel. It's fine as built.

For the same reasons when connections are made to batteries in parallel, each shares an equal current.

Bob

[Larry-NC]

Originally Posted by 5picker

The same with the above reference of connecting two 12v batteries in parallel and the folks that say one lead MUST on the POS of one battery and one lead MUST be on the NEG of the 2nd battery.
I want someone to show me the voltage drop and resistance in a 6" piece of 2 AWG or 1/0 battery cable that connects the two.

The fallacy in the two-battery case is that the proponents of this false theory fail to consider that as the batteries reach full charge, the current tapers off.

Their oversimplified argument simply states that there's voltage drop in the jumpers to the second battery, so the second battery will always be at a lower state of charge.

This weak thinking fails to consider that the closer to full charge the batteries get, the lower the charge current. The lower the charge current, the lower the voltage drop. Finally, at full charge, the voltage drop is zero and both batteries see the same charge voltage.

The effect is that the second battery lags the first in charge state during the charge cycle, but catches up as they reach full charge.

[corn18]

Originally Posted by Larry-NC

The fallacy in the two-battery case is that the proponents of this false theory fail to consider that as the batteries reach full charge, the current tapers off.

Their oversimplified argument simply states that there's voltage drop in the jumpers to the second battery, so the second battery will always be at a lower state of charge.

This weak thinking fails to consider that the closer to full charge the batteries get, the lower the charge current. The lower the charge current, the lower the voltage drop. Finally, at full charge, the voltage drop is zero and both batteries see the same charge voltage.

The effect is that the second battery lags the first in charge state during the charge cycle, but catches up as they reach full charge.

For two batteries in parallel at typical RV amps, it really doesn't matter how you hook them up.
For the OP, I would replace that mess with a nice MRBF terminal fuse rated for the wire size. That would give my electrical OCD the heebie jeebies.