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Alternator size

Discussion in 'Truck & Equipment Repair' started by Mark13, Dec 26, 2007.

  1. Mark13

    Mark13 PlowSite Fanatic
    Messages: 5,796

    I have a newer 105amp alternator and 2 800cca batteries and my lights still dim/blower fan slows down,etc when ever I move the plow up or angle it. I'm assuming my alternator just isn't up to the task of handing my radio, heat, lights, warning lights, and other electronics when plowing. What is a good size alternator to get that will keep up with all the power draw and still not be worked very hard? I'm thinking of getting a custom 250amp but is that overkill?
  2. Mark13

    Mark13 PlowSite Fanatic
    Messages: 5,796

    With 2 800cca batteries should a 150 or 200amp alternator be plenty to power the truck/plow lights, radio(sub/amp), heat, back up lights mini lightbar, and 4 corner strobes all at lower rpm levels?
  3. theplowmeister

    theplowmeister 2000 Club Member
    from MA
    Messages: 2,617

    You don't need that big of an alternator. unless you are going to constantly run the pump. the pump draws150-300 amps when running, thats why the batteries to make up the difference of what the pump draws and the alternator can produce. when the pump is not running the alt charges up the batteries. The pump uses so much power it will dim lights, its OK. what is not OK is if over time (an hour or two) while plowing the battery voltage dose not recover. You probably haven't noticed but if you have your parking lights on and then switch on your headlights your dash lights will dim. It's OK. At home your house lights will dim when your compressor or fridge comes on its OK.
  4. Mark13

    Mark13 PlowSite Fanatic
    Messages: 5,796

    Hmm, It gets pretty dang annoying though.

    If I freshen up/rebuild my plow pump should it draw less power to work? I am unsure if it has ever been rebuilt but it is about 12 yrs old but this is my first season with the plow.
  5. SnoFarmer

    SnoFarmer PlowSite Fanatic
    from N,E. MN
    Messages: 9,883

    Are you still using the stock wiring?
    If so up grade.
    The stock wiring on most trucks is inadequate to handle the load form plowing and the accessories that go along with it.

    Then clean all your connections from the alt to your plow.
  6. Mark13

    Mark13 PlowSite Fanatic
    Messages: 5,796

    I think it has like a 4 guage cable now should I go with 2 guage?
    I have 4 guage linking my batteries together also.
    The alternator and both batteries are new in the last 4 months.
  7. grandview

    grandview PlowSite Fanatic
    Messages: 14,609

    You could cut back on some of the lights!
  8. theplowmeister

    theplowmeister 2000 Club Member
    from MA
    Messages: 2,617

    Rebulding the pump motor may help. but you are still going to get a dimming of the other electrical stuff.
  9. SnoFarmer

    SnoFarmer PlowSite Fanatic
    from N,E. MN
    Messages: 9,883

    Have you up graded your grounds to your body and to the engine?.
    Ground the 2nd batt to your engine too.
    ( I used the same spot the alt is grounded at)

    Some ;)will double up on the +wire from the alt to the batt or fuse block.
    Or install an larger cable, if you do this get a good cable with the ends already crimped on..

    After I installed better grounds and wiring my lights no longer dimmed..

    Ohms law, it takes one amp to push one volt through one ohm of resistance... larger or more wires= less resistance
    Last edited: Dec 26, 2007
  10. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Are the plow cables connected directly to the battery posts (including the ground) like they should be?

    Did you upgrade the stock small gage charging wire from the alt? If not, get a 4 gage cable on it directly to the batteries.. make a real difference on the GM's. The stock charge wire is barely adequate for the job on a non plow equipped truck.

    I'd do an amp test on the motor before just replacing it..

    You can have the plow motor tested right on the truck if you take it to a local shop that has a starting/charging system analyzer. It's a very good way to test them, as your testing it in the actual scenario it's being used in.. Have them check the amp draw on the pump motor with the pump running in relief (full lift or angle and hold it there for a few seconds) Or you can use an amp clamp tester if you know someone that has one you could borrow.
  11. doh

    doh Senior Member
    Messages: 253

    Chebby makes a 105 AMP alt. @ lom RPM. it is what I run.
  12. apik1

    apik1 Senior Member
    Messages: 253

    I have a 98 k2500 with dual 800 amp batteries I had the same problem. I have 4 gauage from the alt to the batteries. But with the heat, wipers, radio, light bar with 4 rotors, 2 set of flashers, and 12 strobes the light dimmed BAD, when I used the plow with the stock alt. I ordered a 200 amp alt, from Discount Battery for $ 189.00 plus shipping, and it came with a under size pully. The differance is amazing, The lights hardley dim at all with it. I wish I would have done it sooner.
  13. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    I like to see a 150 amp minimum alt on a dedicated plow truck.

    And in the case of a plow truck, whether it's batteries, cables or alt amps, more is better. :nod:
  14. Mark13

    Mark13 PlowSite Fanatic
    Messages: 5,796

    Now what would the fun in that be?:D
    My 2nd battery is grounded to one of the bolts that holds my ac pump on.
    Iirc I have 4 guage between the batteries and my stock alt. wiring.
    My plow wiring is Not Directly connected to the battery.
    I can do the amp test at school, the autoshop has all that neat stuff.

    For a start:
    -Redo plow wiring directly to the battery
    -Upgrade alt charging wire
    -Check grounds
    -Anything else?

    Are 4 guage cables connecting the 2 batterys fine or should I get 2 guage cable?

    Then if all else fails get a bigger alternator?
    And getting rid of some of the lights is not an option :D
  15. bribrius

    bribrius PlowSite.com Addict
    Messages: 1,609

    i have the same alt i think. i have one battery which is the same the truck came with new and its eight years old. the lights dim.voltage gauge drops. but it comes up after. i ignore it. all i run for extras is a led rotator on the roof.
    i have a cassette player which i never use and is the extent of the sound system.
    a new alternator is on my list of things to get around to someday. chances are i will never get around to it though until the current alt dies, if it ever does. truck always starts first try. i dont care if the lights dim that much. not enough to go work on it anyway. maybe yours is worse because your running more things..
    Last edited: Dec 27, 2007
  16. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    It's good where it is BUT, run an additional 4 gage cable from the bolt on the compressor to the neg terminal on the 1st battery. This will tie BOTH the battery's, and the engine directly together and also take the load of the stock ground cable between the 1st batt and the engine (which right now is the only thing tying the 2 batt's together)

    4 gage is fine as your cables aren't long enough to need anything bigger.
  17. Mark13

    Mark13 PlowSite Fanatic
    Messages: 5,796

    Ok, I will try to redo my wiring stuff tomarrow and hopefully that fixes the problem for the most part.
    Is the charging wire for the alternator just a normal cable with crimed ends(battery cable) that I can get at any automotive store?
  18. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Even doing all this probably won't totally stop the light dimming issue.. It's just the nature of the beast. But it's worth it to try and diminish it as much as possible.

    Yes you can just buy a 4 gage cable with the ends you need pre-made at most any store. You can leave the stock cable on and just add the extra cable to it.
  19. Mark Witcher

    Mark Witcher Senior Member
    Messages: 605

    The only way to stop the lights from dimming on the truck is to separate the systems. Put the plow on its own battery by using an isolator between the truck battery and the plow battery.
  20. SnoFarmer

    SnoFarmer PlowSite Fanatic
    from N,E. MN
    Messages: 9,883

    An Isolator is for a separate system like a camper.
    It can charge a different kind and size of battery.

    An isolator will not charge the second battery should the primary battery need any power from the ALT.
    An isolator only charges the second battery after the primary battery is charged.

    This still limits you to the cca of the one battery that is running the plow.
    A plow may demand up to 100amps instantly.
    A battery needs to complete a chemical response/reaction to this demand.
    This takes time and can quickly drain a single battery that is not being charged by the isolator.

    The reason you want to double up on battery's for plowing is the high amp draw and the need for the power to be instant.
    Operating your plow with insufficient voltage can damage your electric motor also.

    Also up grading your wiring will let the power flow Better and
    up grading to a larger ALT will also help meet the need for instant amps/power that a loaded down plow can demand.