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  1. #1
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    Default Alternator Issues

    I'm adding electric start to a 6.5hp stationary engine. Being lazy I'd prefer not to have fourth SLA battery to look after, so I thought instead of using a 12V 7Ah battery, I'd wire it to an Anderson plug so I can start if off a 4WD. What I'm wondering is what the alternator* is going to think of being open circuit? any issues there?
    I could leave it off but that would mean if I change my mind I have to take the flywheel off again(see above about being lazy). It also might be nice to be able to use either battery.
    I've been known to over think things.

    *its a pretty simple alternator with one coil and two magnets 180degs apart on the flywheel. A single diode and no regulation.

  2. #2
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    Default

    I don't think it would mind...
    Maybe a resistor across the output, to replace the missing battery. Say 2k ohm, just to eliminate the possibility of a high voltage spike going somewhere it's not wanted.

  3. #3
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    Default

    Could always chuck a dud battery in that doesn't hold charge, and just tee the anderson plug into the lines. Should be able to grab one from a motorbike or rideon mower workshop for nothing if you don't have one... Would probably pick up enough charge that if you run out of fuel, it'll restart without needing to hook the 4wd back up, which might be convenient.

    On a side note, if you're having trouble with this size battery going flat (reading between the lines with the 'look after' comment), the lithium batteries available for motorbikes are pretty awesome. I've got an SSB brand one in my 2 stroke KTM, and it just doesn't seem to go flat. Bike hasn't run since March last year, and I just whipped the seat off to check the voltage before making this post - 12.97V still after 14 months. Bit more expensive than the regular ones, but the convenience of not having to keep them charged might outweigh that for you. There are a few other brands around these days that are supposed to be pretty good, and a bit cheaper than SSB.

  4. #4
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    Quote Originally Posted by Stustoys View Post
    What I'm wondering is what the alternator* is going to think of being open circuit?
    It shouldn't be a problem for the basic alternator you described.
    Chris

  5. #5
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    Thank you gentlemen. I got called away last night.
    It occurred to me at about 4am, given that this is only halfway rectified the peak V on the other side of the waveform isn't doing any harm so as you say, should be fine.

    I haven't had trouble with them going flat yet, but that's because I go around them every month or so and charge them. But then I never actually check the battery V, perhaps I should have done that before reinventing the wheel?

    Given that it looks like the alternator will be fine I'll wire it to an Anderson plug and then I get to choose between a little battery or use the 4WD. I like to have options lol

    Thanks again

  6. #6
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    Quote Originally Posted by Stustoys View Post
    Given that it looks like the alternator will be fine I'll wire it to an Anderson plug and then I get to choose between a little battery or use the 4WD.
    Hang on, I thought you were going to wire the starter motor to the Anderson plug and leave the alternator disconnected (open circuit)?
    Chris

  7. #7
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    Quote Originally Posted by jack620 View Post
    Hang on, I thought you were going to wire the starter motor to the Anderson plug and leave the alternator disconnected (open circuit)?
    As I'm thinking currently, the alternator will be open circuit if I use the 4WD to start and then unplug it. That way if I do use a small battery it will still get charged.

  8. #8
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    Will its finished, for a simple little job it fought me every single step of the way lol
    Amongst other things I had to move the motor in the frame so it "ignition" box didn't hang out the side.
    It started fine in the first test so I prettied the wiring up and the damn thing wouldn't start off the 4WD, popped and banged, then it would start but shut itself off. So I took it back inside onto the bench, grabbed a Anderson plug to battery clip lead I bought a while back for just such an occasion and even that didn't work(that blob of solder on the black lead is doing nothing)! Went back to basics and looks like a bad plug. Put a new plug in and it now starts and runs fine. Now is it a staggering coincidence that the plug went bad the day I fitted the starter or perhaps the ignition coil shouldn't be that far off center of the magnet?

    Anyway its working now and as predicted by you guys the alternator doesn't seem to care if its connected or not
    The starter draws 40amps which is getting up there for 56/.3 cable I believe.(the extension between the 4WD and pump if needed is 93/.32)
    Took awhile but I found out what the thing in the last picture is for, its called a low oil alert, its just some sort of latching transistor(?) the kills the engine even if the oil level switch only closes momentarily.
    Attached Images Attached Images

  9. #9
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    Hi Stuart,

    Alternator Issues-pc-jpg

    Really bad soldered joints ! You need flux and a lot more heat. The solder should become a puddle before it sets.
    Best Regards:
    Baron J.

  10. #10
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    Hi Baron J,

    Just to be clear, that soldering wasn't my work. I purchased the lead to save me making one.
    This is my joint.(ok it looks like I missed one strand )
    I promise to fix the red lead one day lol
    Attached Images Attached Images

  11. #11
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    Hi Stuart,

    Its a bugger when you have to correct someone else’s bodge !

    Though I can't say I'm surprised at what I see there. I've seen a lot of joints like that, particularly in automotive applications, they simply go open circuit or in worst case get hot enough to cause other damage.

    Some people advocate tinning the wire before crimping, which is fine if it isn't going to be subject to vibration or flexing. I like the connectors that are/have a hollow spill or tube to feed the wire into and are crimped to crush the spill onto the wire bundle.
    Best Regards:
    Baron J.

  12. #12
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    Quote Originally Posted by Stustoys View Post
    or perhaps the ignition coil shouldn't be that far off center of the magnet?
    Stu the coil air gap should be .008" - .012", so .010"

  13. #13
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    Quote Originally Posted by BaronJ View Post
    Some people advocate tinning the wire before crimping, which is fine if it isn't going to be subject to vibration or flexing.
    I fall in another camp still lol.
    Given the choice I will sometimes tin after crimping, but only if
    1. there is stain relief
    2. the stain relief can be crimped after soldering
    3. I can be sure that the solder wont wick up past the stain relief.
    Normally I'm not that worried

    Quote Originally Posted by BaronJ View Post
    I like the connectors that are/have a hollow spill or tube to feed the wire into and are crimped to crush the spill onto the wire bundle.
    I bought one of those 8.5ton hydraulic crimpers for this job, pretty happy with it. Its a little fiddly but that's likely because my wire sizes don't match the crimps



    Quote Originally Posted by shedhappens View Post
    Stu the coil air gap should be .008" - .012", so .010"
    I meant the side to side alignment
    I set it at .35mm. After your post I went looking again I found site https://www.engine-specs.net/honda/gx200t2.html Which lists the gap as 0.4mm with... wait for it... +/- 0.2mm tol. So it seems the "business card" really would be close enough. And to think I went to the trouble to find a sheet of cardboard .35mm as 3 pieces of paper were to thin at 0.3mm and 4 pieces to thick at 0.4mm

    I found this interesting, from a B&S FAQ I'm told.
    "An armature air gap that is too wide will prevent spark. Not true. Well, sort of not true. Briggs & Stratton air gaps cannot be made too wide to prevent spark providing the coil is healthy and the engine is spun over fast enough. A wide air gap, say .030" will ever so slightly retard the ignition timing as the magnetic field takes longer to build within the coil windings."

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