Low watt solar battery tender polarity

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.
Comments
i can't see your PV. cables, meter settings or battery, so I have no idea what's happening,
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,
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:
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
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.
-Bill
2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.
It has been less true now--But in many decades past, positive ground for vehicles and equipment was not uncommon.
-Bill
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.
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