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Just finished dual alternators

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Blue85, Oct 29, 2002.

  1. Blue85

    Blue85 Troll Premium Member

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    Instead of breaking my piggy bank for a 140Amp or more alternator, I just went down to the local parts counter and paid $30 for a stock replacement alternator. I left my existing one alone. The A.I.R. pump didn't work anyway, so I took it out and mounted the second alternator there. It runs from the pulley that the air pump used to run on, I just needed a shorter belt. Now if either one fails, I still have a working one. Plus, I can collect the lifetime warranty on either one, since they are the same.

    To mount it, I had to space the mounting bracket out 1/2" to make the pulleys line up. I removed the bracket from the block and put two nuts behind it as spacers, using bolts that are 1/2" longer. Then I had to hack off the bottom of the flat bracket that mounts to the bottom of the alternator and to the water pump housing. This is because the alt is about 2" bigger in diameter than the air pump. I cut off the bolt hole that used to hold the air pump in adjustment and drilled out the Battery ground cable hole to hold the adjustment bolt. I reused the stock slotted adjustment bracket from the AIR pump. It had an offset bend in to to recess it, so I bent it out to straight to get the needed 1/2".

    For wiring, I put heavy ring terminals on some 10gauge cable and ran it about 2.5 feet from the output terminal to the starter motor. I would have used bigger cable, but this is actually bigger than what is currently running to the 1st alternator (maybe I should upgrade that sometime soon?) Then I used a new alternator connector and spliced into the existing alternator's two wires so that they are both wired the same.

    Granted, they will never share the load evenly, but as long as there is enough demand to get one up to it's max output (for that engine speed), the voltage will dip enough for the other one to charge. With a really heavy load, the voltage will be low enough for both to give max output.

    The only bad thing so far is that the pulley for the 2nd alternator is smaller then the other two pulleys on the water pump, so the 2nd alt spins slower. This is counter-productive to my goal of getting more current at idle, but it does still charge some at idle with the 1st alternator disconnected. If I ever find a cheap water pump pulley that has 3 of the larger size grooves, I will swap that on.

    So I put about $50 into the whole thing. I'll get $15 back if I ever come up with a core to return.
     
  2. Rolled

    Rolled 1/2 ton status

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    How much was the 140 amp? I too am going to go with dual batteries and a high amp alternator. I never thought of putting in two. Is it electricly safe to do that?
     
  3. Blue85

    Blue85 Troll Premium Member

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    </font><blockquote><font class="small">In reply to:</font><hr />
    How much was the 140 amp?

    [/ QUOTE ] Summit sells them for $200 and up. I don't know if better deals are available. One problem I do know of is that generally the higher output units do it at high rpm and sometimes the idle outputs are lower than stock units. There is a "big case" GM alternator that pumps it out down low, but they are pricey new and hard to find used. I think they are from ambulances, medium dutys and stuff like that.

    Electrically safe? Obviously I think so. One alternator will not hurt the other. It's just that one will always carry most of the load until the demand is really high because the regulators will never be matched exactly. If your battery voltage is really low you know that they will both be full on because you are well below the desired voltage of both regulators.

    I too am planning on adding a second battery. I want a spiral cell, but don't really want to pay for one. It will power things when the engine isn't running, so I can drain it with the stereo, dome lights, etc and still have a full battery for starting. When the engine is running, both will be in parallel. I will build a custom controller and solid-state switch to do this since solenoids wear out and solid state relays of the necessary rating are over $100. Diodes drop too much voltage for both batteries to charge optimally. Putting one alt on each battery doesn't allow you to have the full potential power while running because there will still be diodes or a solenoid inbetween.

    My plan is to physically put the stereo, dome lights and hazard lights all on the second battery. Both alternators charge the primary battery. When the engine is running, a solid state switch will tie the two circuits together. The oil pressure switch is a great signal to use for this. Then I will have a toggle switch to manually engage the solid-state switch to allow starting with parallel batteries. This switch I am talking about will be made from 6 IRL3803 MOSFETS in Super-220 packs, which should be good for about 300 Amps continuous and surges big enough for the starter motor. We will see. This is important since a really low auxilliary battery will charge at hundreds of amps from the primary battery and alternators after the engine starts.

    Let me know if you have any better ideas as I am still thinking this through.
     
  4. TopOff

    TopOff 1/2 ton status

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    FYI: Here locally Kragen (Chuck's or Checker's auto) has their Spiral Cell battery on sale for $99.-
     
  5. Blue85

    Blue85 Troll Premium Member

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    Thanks for the info. We don't have Kragen, Chuck's or Checkers here. I think NAPA has their own spiral cell, so maybe I should keep my eyes open for that. I think Optima redtops are about $160 and yellow tops $180. Don't know the difference in quality between Optima and the knockoffs.
     
  6. mattyblazer

    mattyblazer 1/2 ton status

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    I believe that the batterys are all manufactured by exide or whoever owns them now. The local dealer (chevy) told me that a 140 amp alternator can harm the harness.
    A boat switch works well for managing the batterys if you dont mind manual switching.

    just my 2 cents
    Matt
     
  7. Rolled

    Rolled 1/2 ton status

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    Blue85 - Sounds like you get along with electricity /forums/images/graemlins/grin.gif

    I am about a month away from adding the extra batery. Please post your progress as I am very interested in your circuitry. I was just going to add switch or two but your way seems much slicker.
     
  8. TopOff

    TopOff 1/2 ton status

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    RedTops are all over the 'Net for $124. But shipping usually sucks.

    I would get this battery for you except when you want to use the 8 year warranty (first two yr is replacement)... you will be POOH out of luck. /forums/images/graemlins/deal.gif

    Neat setup on the alternators. Seems simple, clean and best of all it uses OEM parts (reliability).

    I would feel better if each alternator went to it's own battery. Use a starter solenoid and connect the two batteries when you need them. I guess it really depends on your demands of the electrical. I would run one battery dedicated with an alternator to the winch, the other battery and alternator to the rest of the truck. Then if needed I can connect the two batteries for winching or startiing duties.

    I wonder how the military dual alternators work/wired? Anyone?
     
  9. DieselDan

    DieselDan 1/2 ton status

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    I've been told two altenators will tend to "fight" one-another for the load, as when you jump start one vehicle with another. I don't really know if this is fact or lore. Anyone care to verify or disprove this?

    I do know that the CUCV used isolated ground altenators, but this may had more to do with the 12V/24V series wiring. I've heard some Fxrd Super Dutys run a two altenator system, 'wonder how that works /forums/images/graemlins/ears.gif
     
  10. Highlander

    Highlander 1/2 ton status

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    For a 140 Amp Alternator you could go and look at Summit Racing they have one for 169.00 and if you around their web site or get the Catalog you could find a better deal. I got my 140 at Four Wheel parts for about 140.00 they gave me a discount for being a member of CK5. As for batterys just about everyone has a Gel battery now, so look for the best deal.

    Eric
     
  11. imiceman44

    imiceman44 1 ton status

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    If you put two alternators, they will naturally be grounded so they basically share the load, they will not fight for it just feed into it, like 2 batteries in parallel. In case you need a seperate circuit then you need to have an isolated mount, I think that is the case with the hummers.
    In AC currents, you can't link 2 phases together, but in DC current you can with no problem.
    As for the load being on only one alternator, I have to see it with an amp meter, the ones I have seen shared equally.
    I will be doing exactly that in the next few weeks and I will let you know if I find it different.
     
  12. FRIZZLEFRY

    FRIZZLEFRY 1/2 ton status

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    I did almost the same thing but for my onboard welder.The way I did mine I reused the same belt.

    [​IMG]


    Got any pics?
     
  13. BARRAZA

    BARRAZA 1/2 ton status

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    One of the CUCV alternators puts out 12v and the other 24v. When you convert a CUCV to 12v, one is removed. I do not see the use in having two alternators feeding one battery, unless they are regulated by one regulator. My understanding is that one of the alternators (the one with the higher turn on regulator voltage)will supply all the load unless the voltage remains below the threshold voltage of the second alternator even after the first alternator is putting out its max. A two battery system with a primary an secondary battery might benefit from a second alternator, but its overkill unless you are using very large amounts of power. I think you will easily spend more than the high output alternator would have cost in the first place.
     
  14. Dirty Dave

    Dirty Dave 1/2 ton status

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    Actually both alt's on a CUCV are 12volt. They combine to make 24volts. See this link.....

    web page
     
  15. BARRAZA

    BARRAZA 1/2 ton status

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    Didn't say they weren't 12v, just that one puts out 12v and 24v out of the other - 12v input to the second one provides 24v out. Guess I could have been clearer. Thats why there are two, and why they are floating ground. They can actually be interchanged.
     
  16. fr8train

    fr8train 1/2 ton status

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    Hey Dan. The Turds may run them, not for long though. They tend to last about 6mos. to a year then get a really big spike and take out one another. My dads company had a F450 with one that took out two laptops and a OBA compressor. /forums/images/graemlins/angryfire.gif Yet again, one of the many reasons, why my dads company doesnt do anything but GM/Top Kick. Also there is a dead and burnt F550 that the govt. has left at our other location that has yet to be delt with. Talk about a waste of our tax money, thats 3 Turds and 4 Dumpdges that our welders have gone thru. And the govt. charges it to you and me, and the other "big 2" get away laughing /forums/images/graemlins/angryfire.gif /forums/images/graemlins/angryfire.gif /forums/images/graemlins/angryfire.gif
     
  17. Blue85

    Blue85 Troll Premium Member

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    </font><blockquote><font class="small">In reply to:</font><hr />
    I would feel better if each alternator went to it's own battery. Use a starter solenoid and connect the two batteries when you need them

    [/ QUOTE ]
    I considered this and I may actually switch over to this once I get the second battery. You can't use a starter solenoid, though, as they are only for intermittent use and pull like 10Amps themselves. A continous duty solenoid is OK, but they wear out after a while and do take some current to keep pulled in. If I go this route, I will use the solid state switch (once I build it).

    I have considered, too, just keeping both circuits seperate all the time, but if I ever add a winch [/dreaming mode on] I will need all of the power I can get [/end dream].
     
  18. TopOff

    TopOff 1/2 ton status

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    "If I go this route, I will use the solid state switch (once I build it)." - Blue85

    Tell me more about this! /forums/images/graemlins/ears.gif

    right now I have a simple 90 amp battery isolator on my setup. Then a Starter solenoid to connect the two batteries when I need it. Apparently my wiring job isn't too good, as when one battery was COMPLETELY dead, the solenoid and wiring weren't enough to kick the engine over. I guess the dead battery had too much of a load on the good battery. I might have to look into one of those battery isolator / switchs. And/or find something from an RV shop.

    Keep us posted on your project!
     
  19. Executioner

    Executioner 1/2 ton status

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    Ya I am interested in this Mosfet Switch Idea too !
    Please tell us more.
     
  20. Blue85

    Blue85 Troll Premium Member

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    It's simple. I use a bank of 6 MOSFETs in parallel, each with .006 Ohm "on" resistance, rated for 80A, all mounted to a decent sized heatsink. Obviously, MOSFETs like this are n-channel, so I need more than 12V to drive the gates. For this, I will use a solid-state DC-DC converter to get a 24V supply. I have all of the parts on hand, but have not constructed it yet since I don't have a second battery yet. All of the parts were free to me: let's just say I have access to some good scrap bins. /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
     

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