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No voltage

Discussion in 'Daihatsu Hi jet' started by Hegels, Nov 27, 2020.

  1. Hegels

    Hegels New Member

    1991 Hijet Jumbo

    Hello all, I've been troubleshooting an odd electrical issue i experienced recently.

    The gist of my problem is this. I came out from running an errand to the store and found that the truck had no electrical power whatsoever. I got home and today I began to troubleshoot.

    1)I found that the negative terminal was pretty badly corroded so the cable was replaced & I added an additional ground to the transmission.

    2) 12v was found from the starter lug to chassis ground.
    3) 12v was not found at the alternator charging lug.
    4) when I jumpered between the main charging lug and the battery terminal the truck started functioning again.

    Does the alternator charge go through a main fuse or should it essentially just go right back to the battery.

    I can make a new cable up if it goes back to the battery as a straight shot but I don't want to bypass any fuses if its meant to have one.

    thanks,
    Steve
     
  2. Jigs-n-fixtures

    Jigs-n-fixtures Well-Known Member

    On my S110P, there was a wire which ran from the alternator main lug through the starter terminal and from there to the battery.

    There wasn’t a fuse in it. Might have been a fuseable link I missed.
     
  3. Roadster

    Roadster Active Member

    Some alternators require the field to be "excited" momentarily before it will output any power. It sounds like this is the case with this one... you have a heavier gauge main wire going between the alternator + terminal to the battery - usually no fuse. You have a heavier gauge ground cable from the alternator case to the engine block (or similar). There is a wire to the charge light on the dash from a two post terminal block on the alternator, and an "exciter terminal" (usually marked "2"). This wire only needs power momentarily and so connecting it to the main starter solenoid supplies power only when the starter is activated. Once the engine starts and the alternator is running, there is no need to activate the "excite" wire - the alternator will put out power as long as the engine is running. The alternator needs to be excited again on the next start-up, however. Usually there is no fuse on this line. Hope this helps!

    Roadster
     
    Limestone likes this.
  4. Hegels

    Hegels New Member

    That does help me to understand how they work, and also lets me know that I can essentially run a new wire from the alternator to the battery and all should be well. I just wanted to clarify that without power jumpered from the main charging lug to the battery I essentially get no power to the truck whatsoever. I'm going to do a bit more tracing and see if i can sort out where the break is before committing to running a new wire.

    Thanks,
    Steve.
     
  5. Roadster

    Roadster Active Member

    Steve;

    The 4 or 6 gauge wire from the alternator to the battery is the way the alternator gets the power to the battery; the small gauge wire from the alternator field terminal (not the main power + terminal) to the starter positive is what tells the alternator to start charging - this is just momentary, and could be connected to the ignition switch start position instead. In our case, from what both yourself and Jigs said, it sounds like the alternator field is excited by a wire from the starter. But energizing the alternator at the main terminal from the battery seems strange. As there is already 12 volts at the alternator terminal from the battery, a 12 volt + wire from a momentary source (starter solenoid) doesn't really accomplish anything except activate the starter continuously...which isn't good...

    The other issue is, if you activate the field continuously, when field will draw current even when the alternator (and engine) are not running and the ignition is off, draining the battery. That is why the excitement is only momentary.

    On the other hand, if this is a true "one wire" alternator, it would probably be "self exciting" and not need a field wire to the starter or switch...and the field is deactivated on shut-down. I haven't checked if there is a terminal block ("1" and "2") on the back of my alternator; because there is an alternator charge light on the dash, I suspect there is... (usually, "1" is the charge light; "2" is the field)

    Roadster
     
  6. Roadster

    Roadster Active Member

    Hmm.. The alternator main wire might go to the starter solenoid "hot" side and from there to the battery ("4 gauge") using that post on the solenoid as a through connection point instead of the battery being directly connected to the alternator. The field exciter wire would be connected to the "starter" side of the solenoid for momentary operation... Adding a wire from the battery directly to the alternator as well would not be necessary...it's already connected together.

    Roadster
     
  7. Jigs-n-fixtures

    Jigs-n-fixtures Well-Known Member

    I did a post on the Mini-Denso alternators used in the Hijets a while back: https://minitrucktalk.com/threads/better-alternators.18319/

    I think that the stock unit on your S80-series is a “three” wire system.

    One is the large charging wire which takes the output to teh battery. On your Hijet, it goes down to the solenoid at the starter and then back up to the battery.

    One small wire is wired to the ignition switch controlled side of the fuse panel, and the alternator will charge when this gets current from the ignition switch. I think this wire shares the fuse marked engine, and also feeds the hot side of the coil.

    The second small wire goes to the warning light on the dash.

    If your alternator is bad, you can get them rebuilt fairly easily, because this model is used on a plethora of small equipment from generators to mini-excavators. And, with a little looking you can find everything to rebuild them on eBay. If you have to replace/rebuild you alternator you might want to look into a higher amperage one. I increased the output on mine up to 90-amps from the stock 35-amps because I have enough lights on the truck for when I’m plowing to have low battery issues if I keep them all on and run the electro-hydraulic plow. And, I used the “four wire” version, because I want the alternator to sense the voltage at the battery and charge the battery fully, as opposed to sensing at the alternator.

    Your symptoms could be caused by just a fuse that is intermittently closed. Alternator could be just fine. The wiring is getting old, and gremlins will appear from time to time.
     
  8. Roadster

    Roadster Active Member

    Ah ha! Thanks Jigs - your truck has a lot of loads to consider compared to my simple truck... I do find turning on the heater fan does drag the idle RPM down about 75 RPM... I took a cursory look at the back of the alternator as best as I could, and could only see the output terminal. However, there could be something I can't see well back there. It is a small two bolt Denso unit; I can't see the amps (yet). I'll have to check some more - there has to be a connector somewhere - perhaps I need to look from the bed panel instead of just under the driver's seat.

    Roadster
     

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