Low watt solar battery tender polarity

stmar
stmar Solar Expert Posts: 373 ✭✭✭
in General Solar Power Topics #1
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.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    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,
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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    gen: http://tinyurl.com/LMR-Lister ,

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  • stmar
    stmar Solar Expert Posts: 373 ✭✭✭
    #3
    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:
    Picture of BulletSAE Connector to Powerpole Connector - 1 ft long

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    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
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #5
    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. :)

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  • stmar
    stmar Solar Expert Posts: 373 ✭✭✭
    #6
    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?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #7
    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
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • stmar
    stmar Solar Expert Posts: 373 ✭✭✭
    #8
    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.
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,102 ✭✭✭✭✭
    #9
    What DMM are you using?  H have had cheap Harbor freight meters do this.

    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,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • stmar
    stmar Solar Expert Posts: 373 ✭✭✭
    #10
    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.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #11
    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
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • stmar
    stmar Solar Expert Posts: 373 ✭✭✭
    #12
    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.
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #13
    maybe it would elimiate some confusion if you use different coloured Power pole connectors for each charger...?  then no mix up...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • stmar
    stmar Solar Expert Posts: 373 ✭✭✭
    #14
    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.
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