Low watt solar battery tender polarity

stmar

I have several battery tenders, solar and AC, that I use for my vehicles; trucks, ATV's, tractors, etc. The AC tenders detect and adjust the polarity. Does polarity make any difference with small, like 10 watt and 2 watt, solar panels? The reason I ask is that the alligator clips, red and black, are different for the different panels. I just got a 2 watt and using the alligator clips that came with it but my voltage reading is negative which tells me the polarity is backwards; black from the battery to black on my meter and red from the battery to red on my meter produce an negative reading. On my 10 watt it reads positive. Confused as to the difference in solar panels and if negative reading will damage the battery or if I should just switch clips to get a positive reading. Thanks and sorry to ramble but DC voltage is confusing.

mike95490

Connecting a solar panel backwards to a battery will discharge it,
  i can't see your PV. cables, meter settings or battery, so I have no idea what's happening,

stmar

mike95490 said:

Connecting a solar panel backwards to a battery will discharge it,
  i can't see your PV. cables, meter settings or battery, so I have no idea what's happening,

So bottom line is if my meter is reading negative it will discharge instead of charge the battery? Then I just need to switch clips to get a positive reading? It really is confusing that different products have the positive red and negative black going to different pins on the connector, they are similar to this type of cable only with alligator clips on one end and molded connector like the one with the exposed pin on the other:

BB.

And connecting a solar panel backwards will generally ruin it. Solar panels are very large "diodes"--And when connected backwards, very large current flow from the battery will cook the cells and electrical connections (large or small solar panels).

Some solar charge controllers are "polarity protected"--But they simply will not be damaged if connected backwards. They will not charge if connected backwards.

-Bill

PNjunction

This isn't an uncommon problem when changing one manufacturer's clamps for another.  For example, most Harbor Freight / Sunforce / Coleman panels and kits have their SAE connectors wired for a different polarity than most charger manufacturers.

Ie, swapping the clamp set from an HF panel kit with a slightly beefier set from a Battery Tender maintainer results in a reverse polarity.

So when dealing with SAE connectors in general, it is always good to verify polarity first - or at least ohm it out / compare the wiring to the original oem cable.

And, SAE connectors are just terrible in the first place.  Many are oxidized or poor fitting resulting in a high-resistance contact with an attendant slight voltage drop.  Both are bad.  If you can, use the Anderson connectors as shown above for much more reliability.  You can crimp your own, or just buy pre-made sets.  Connector quality, even at the dinky maintainer level, is crucial - you have no power to waste.

stmar

The interesting thing is I am using the cable that came with the panel. It is a 2 watt Colman maintainer. Can I assume they screwed up at the factory or is there another rationale?

BB.

Don't know--But try to verify the panel output polarity and current in full sun with your DVM (digital voltage meter). You should see > 13.5 volts and >~0.5 amps (for the 10 watt panel if full sun).

-Bill

stmar

Now I am really confused?? I just checked my lawn tractor battery, not connected to anything, and I am getting a negative reading when I go red to pos and black to neg on my meter. What would cause a battery to give such a reading? Looks like the panel may not be the culprit after all.

littleharbor2

What DMM are you using?  H have had cheap Harbor freight meters do this.

stmar

It is a Sperry DM-6400. It reads correct on my 10 watt that I have hooked up to my truck right now. I will check some other batteries to test the meter.

BB.

I have confirmed my readings on my car battery/electrical system if I have questions about the volt meter is readings.

It has been less true now--But in many decades past, positive ground for vehicles and equipment was not uncommon.

-Bill

stmar

I think I have solved the problem or at least on the road to it and sorry for the runaround but maybe someone will benefit. I discovered that I had in fact substituted the beefier clamps from another charger and have been "charging" my lawn tractor battery with a reverse polarity from my 10 watt panel and this reversed the polarity of my battery. I had been using the 10 watt panel to charge my trolling motor battery and everything was correct, I have a Minncota battery box and used the lighter outlet and cable. So when I started charging my tractor battery I used beefier clips from a tender instead of the ones that came with the panel. I hooked the same setup to my truck yesterday and wondered why I was not getting a charge in full sun. Today I changed out the clips for the ones that came with the panel and it started charging my truck battery right away.
I guess the moral of the story is to not mix and match different manufacturer or types of chargers and cables and always check voltage readings before you ruin a battery or charger. I know the tractor battery is probably toast and I hope I did not damage my 10 watt panel, it seems to be working now. Thanks for all the input, it helped me.

westbranch

maybe it would elimiate some confusion if you use different coloured Power pole connectors for each charger...?  then no mix up...

stmar

Definitely a good idea to id cables that go with correct charger. One thing I have found is that "heavier/beefier" is not always better, stay with the original. Thanks.