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Topic: Positive/Negative ground (not necessarily RV related) (Read 538 times) previous topic - next topic

Positive/Negative ground (not necessarily RV related)

Actually, probably not RV related except I have a system with a battery and a solar panel (not quite the capacity of your RV but then, its just a matter of scale).

Preface:
I am enjoying sailing in my Pearson Ensign on Lake Superior this summer. However, it does rain occasionally and I expect my electric bilge pump to take care of the water in the deep bilge.

I have a relatively small 12v battery which is connected to a small solar panel and it worked great until I rewired the connection to the pump. No,  that's not right.. it initially worked great.  Now it doesn't. The battery has a (+) stamped on one terminal and a (-) on the other.
I thought I had been cautious and rewired both the battery and the solar panel feeds as they had been.


Diagnostic process:
At some point, I think during the honeymoon period (when the system worked), I seem to remember using my DVM to check the battery voltage. I ignored the 15+ volt reading as incorrect.

* I measured disconnected battery's the state of charge. Red to red, Black to black. The DVM read - :o 12.22 (or there abouts).
I switched the meter leads - Red to negatively marked post, Common (black) to the post marked (+). Read positive 12.xx.

*Thinking I must be doing this wrong I popped the hood on the jeep and measured Black lead to negative post, Red lead to Positive and got what ??
A positive number just as I was expecting.

Theory:
My small battery (used in riding lawnmowers and motor cycles) has poles (stampings) different from automobile batteries ...
But I have never run across such.

Question(s):
The new bilge pump expects a fuse on the positive wire.
If I get a positive potential by measuring from the negative to the positive posts rather than the other way around which do I fuse?.
How do I connect the solar panel?
Am I over thinking this rather simple issue?

What is really happening?

thanks
Elliott & Mary Bray
ex. 1996 36' U295 - Build 4879
ex. 2018 Coachmen Leprechaun 319MB
 

Re: Positive/Negative ground (not necessarily RV related)

Reply #1 –
Check to make sure the black wire on the DVM is connected to the right "common". Sometimes there is a separate common for measuring current (amps) from the one used to measure volts and ohms.

I cannot imagine a battery labeled + being the negative contact. It's a recipe to let the smoke out. For instance, that bilge pump would destroy itself to protect the fues. :D

Craig
1993 U225 36' Unihome GV with PACBRAKE exhaust retarder, Banks Stinger and Solar Panels.
Toad: 1999 Jeep Wrangler 2-door soft-top.

"No one has ever had to evacuate a city because the solar panels broke."

Re: Positive/Negative ground (not necessarily RV related)

Reply #2 –
I just Googled the subject and it looks like it's possible to reverse charge a battery.  I can only guess you might have hooked up the solar charge with the leads reversed.  The battery discharged to 0 volts and then started charging with the reverse polarity:
Battery Myth | Can a Battery ?Reverse? its Polarity?

In so far as which line to fuse it really makes little difference assuming your boat is fiberglass and not metal.  Yes, normally it's the positive lead that gets fused.  The reason is that the positive lead could get pinched somewhere along it's path and get shorted to the hull; that only happens if you have a metal hull and the hull is connected to ground.
John Fitzgerald
1991 U300 (SAI) Side Aisle Island Bed 40'
Detroit 6V92 with Allison Retarder
Meridian (Boise), Idaho

Re: Positive/Negative ground (not necessarily RV related)

Reply #3 –
The other day I inadvertently connected my 33-watt solar panel to a battery in reversed polarity and it let all the smoke out of the diode in the panel.

Craig
1993 U225 36' Unihome GV with PACBRAKE exhaust retarder, Banks Stinger and Solar Panels.
Toad: 1999 Jeep Wrangler 2-door soft-top.

"No one has ever had to evacuate a city because the solar panels broke."

Re: Positive/Negative ground (not necessarily RV related)

Reply #4 –
Measure twice, cut once. :o  I do violate that on a regular basis. Bummer to hear about your panel.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Positive/Negative ground (not necessarily RV related)

Reply #5 –
Quote from: Pierce & Gaylie Stewart –
Measure twice, cut once. :o  I do violate that on a regular basis. Bummer to hear about your panel.

I have another one just like it. And I suspect I can replace the diode. If it fried an element in the array then I'm done with it. It was going to be the charger for the little battery on the fishing skiff. Just not paying close enough attention to a battery in a weird location. Lots fo excitement, though. :P

Craig
1993 U225 36' Unihome GV with PACBRAKE exhaust retarder, Banks Stinger and Solar Panels.
Toad: 1999 Jeep Wrangler 2-door soft-top.

"No one has ever had to evacuate a city because the solar panels broke."

Re: Positive/Negative ground (not necessarily RV related)

Reply #6 –
Quote from: JohnFitz –
I just Googled the subject and it looks like it's possible to reverse charge a battery.  I can only guess you might have hooked up the solar charge with the leads reversed.  The battery discharged to 0 volts and then started charging with the reverse polarity:

I've seen this happen before on small batteries like the one OP has (small motorcycle or lawnmower battery). It confused the heck out of me at the time as well!
1998 U270 34'

Re: Positive/Negative ground (not necessarily RV related)

Reply #7 –
When you stated that you went "Red to red black to black" was that to a red and black wire leading to the battery, or were you on the + and - on the battery?
If you tested on a wire that leads to the battery and not the battery itself, maybe the wires are reversed on the battery.
Just a thought.
Michael Baldacchino
'97 40' U320

Re: Positive/Negative ground (not necessarily RV related)

Reply #10 –
I appreciate the info re: Reversed Charging.

I'm sure that's what happened. At one point in the tale (not worth being a 'saga') I had jumpered across the wrong poles.

I took it back to Menards (Midwest super Lowes/HD) here in Marquette.
I didn't have the receipt but they still carried it and the manufactured date on the case was just over a year old.

They took it back and gave me a store credit slip. Since I didn't have the receipt the best they could do was the lowest price during the last year.

The replacement battery cost me $3.00 :dance:

Thanks for the help...


Elliott & Mary Bray
ex. 1996 36' U295 - Build 4879
ex. 2018 Coachmen Leprechaun 319MB