Wiring small alternator as supplied by Locost SA

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Wiring small alternator as supplied by Locost SA

Postby andredp on Wed Apr 09, 2008 8:21 am

Hi Everyone

Wanted to post this a while ago already(after a lot of guys asked me about it), but slipped my mind. Better late then never ;)

Red wire with fuse connector(in first pic) = battery sense wire - goes directly to the battery positive via a fuse, 500mA or smaller.
Grey/black wire = warning light/ignition light
Red wire = ignition switched power

Image

More focus...
Image

Hope this helps.
Andre'
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Re: Wiring small alternator as supplied by Locost SA

Postby johan13 on Sat Jan 02, 2010 4:02 pm

Hello Andre. Maybe I’m misunderstanding what you mean with “Red wire = ignition switched power” because I have zero power here?
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Re: Wiring small alternator as supplied by Locost SA

Postby BradW on Sat Jan 02, 2010 4:29 pm

johan13 wrote:Hello Andre. Maybe I’m misunderstanding what you mean with “Red wire = ignition switched power” because I have zero power here?


This means you must supply the alternator with +12v from an ignition switched supply, IE the wire i 12volts when the ignition is on, and 0 volts when the ignition is off.

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Re: Wiring small alternator as supplied by Locost SA

Postby johan13 on Mon Jan 04, 2010 7:43 am

Just checking that (1) the “Grey/black wire = warning light/ignition light” is positive when the alternator is functioning correctly and earth or negative when there’s a problem with the alternator or when it’s not turning AND the other side of your warning light is thus positive? (2) the screwed / nut connector also seen on Andre’s photo must be earthed?

Thanks for the help.
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Re: Wiring small alternator as supplied by Locost SA

Postby andredp on Mon Jan 04, 2010 8:14 am

Correct on warning light, other side must be positive but switched positive from ignition.

Screwed nut connector is for large charging current, ie BIG wire directly to battery. The alternator is earthed through it's body/casing.
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Re: Wiring small alternator as supplied by Locost SA

Postby muller on Mon Jan 04, 2010 9:39 am

If you prefer shortcut wiring you can wire both red wires to switched + (and not one of them directly to the battery). In cars like ours with very few electrical devises this works just fine.

If you want to use an LED for a warning light then have a look here for a wiring diagram http://www.locost.co.za/forum/viewtopic.php?f=6&t=1716
Anton

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Re: Wiring small alternator as supplied by Locost SA

Postby andredp on Mon Jan 04, 2010 11:00 am

muller wrote:If you prefer shortcut wiring you can wire both red wires to switched + (and not one of them directly to the battery). In cars like ours with very few electrical devises this works just fine.



I wouldn't advise this on a road car. The sense wire will "see" the loss in voltage on the sense wire(if wired through ignition) and up the voltage to compensate. This will hurt the battery, since it will be permanently overcharging. These small alternators is also fairly sensitive, so you don't want to put strain on it for nothing.
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Re: Wiring small alternator as supplied by Locost SA

Postby muller on Mon Jan 04, 2010 1:26 pm

andredp wrote:
muller wrote:If you prefer shortcut wiring you can wire both red wires to switched + (and not one of them directly to the battery). In cars like ours with very few electrical devises this works just fine.



I wouldn't advise this on a road car. The sense wire will "see" the loss in voltage on the sense wire(if wired through ignition) and up the voltage to compensate. This will hurt the battery, since it will be permanently overcharging. These small alternators is also fairly sensitive, so you don't want to put strain on it for nothing.

Stupid Q alert..... Is there really a significant drop in Voltage measure at the battery or at the ignition switch (or FIA cutout as in my case)? I know you get a drop in voltage over the length of a wire, but generally we use thick wires and the distances involved are very short.
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Re: Wiring small alternator as supplied by Locost SA

Postby andredp on Mon Jan 04, 2010 9:01 pm

Well on a racer the electronics is usually much simpler then on a road car, but if you use big wires they should have minimal drop in voltage. The thing is that with light weight cars like ours, you want to save weight and using smaller wires can help you achieve that. One has to just realise that smaller wires has a bigger drop in voltage and you need to be aware of that and compensate for it. I use very thin wires on my racecar, and on the management I "see" a drop of around 0.5V from what I measure on the battery. This is not too bad, but if you consider that you now run the alternator sense wire on the same path, the alternator will think it has a 0.5V drop on the connection to the battery, and will up the charge by 0.5V. This will be fine for your car electrics which should be rated to 16V for short periods, but if you continuously charge your battery with the extra 0.5V, it will definitely shorten it's lifespan. By how much I cannot say, but it does. The alternator is set up to charge the battery at the absolute ideal voltage to try and maximise it's life, which is why they started using sense wires, but improper connecting the sense wire can result in limited battery life span.

The other thing to keep in mind, is the kind of battery you use. Regular automotive batteries want ideal voltage and it gets that from the alternator. When you "cheat" and use "other" batteries like we do ;) it might not matter, since they will not be charging at optimal voltage anyway, so why bother with properly adding the sense wire :) Only on a racer though, where replacing a battery every two or 3 years may not be such a big deal in the bigger scheme (budget) of things. While on that, I must say I am impressed with these little buggers, mine is still going as strong as always after 2.5 years of use in the racer, and this is with doing night races, driving home recently in the rain at night with light on brights after our social, even forgetting the ignition on for a couple of days some time back. Thumbs up for using these batteries :D
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Re: Wiring small alternator as supplied by Locost SA

Postby johan13 on Tue Jan 05, 2010 6:20 am

Andre, what battery are you using? I've just got the big old standard Bantam one?
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Re: Wiring small alternator as supplied by Locost SA

Postby andredp on Tue Jan 05, 2010 7:09 am

Johan, I am using a small "UPS" type battery, 18AH rating. Some of the other guys are using fairly big bike batteries which also seems to be good. Most electronics guys will tell you 18-25AH batteries are way too small for a car, and they may be correct, yet these do seem to work well. I know Anton has had one or two fail on him, maybe he can give some input on his ones?
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Re: Wiring small alternator as supplied by Locost SA

Postby muller on Tue Jan 05, 2010 1:00 pm

andredp wrote:Johan, I am using a small "UPS" type battery, 18AH rating. Some of the other guys are using fairly big bike batteries which also seems to be good. Most electronics guys will tell you 18-25AH batteries are way too small for a car, and they may be correct, yet these do seem to work well. I know Anton has had one or two fail on him, maybe he can give some input on his ones?


I've had about 4 fail on me, no idea why (maybe its my shortcut wiring?) I've actually gone back to using a small car battery out of frustration. To compensate for the extra 5kg I've relocated the battery to the passenger compartment (in a battery box as per regs) to lower the COG.
Anton

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Re: Wiring small alternator as supplied by Locost SA

Postby andredp on Tue Jan 05, 2010 6:36 pm

I don't think it is wiring, if I must guess I will probably say it is due to the cranking you do to build oil pressure first before you start your car, but hard to say.
Andre'
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Re: Wiring small alternator as supplied by Locost SA

Postby ross on Tue Jan 05, 2010 7:40 pm

A normal lead acid battery is able to stand overvoltage as there is space in the individual cells that allow for a certain amount of expansion, also the plate/insulator cell assemblies are not forced into the battery box they just fall in there, under gravity. With a sealed battery the plate/insulator assemblies are forced into the boxes using a shoehorn technique, developed by chloride. The insulating material between the plates is similar to blotting paper so that it absorbs the acid and turns into a kind of paste, between the lead plates. If the battery is overcharged it overheats and eventually the lead plates buckle and push through the paste resulting in a short. The small sealed batteries are designed to be constantly trickle charged, with relatively deep draining when the power supply fails.
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