charging voltage

[cri_ag]

my old man has a fishing boat with a 25 hp motor, it has a alternator fitted and a deep cycle battery. the charging wires were disconected from the engine while the boat dident have a battery for a while, now it has a new battery but the old man cant remember which wire goes where! i think ive got it figured out but when i run the motor the voltage varies from ~10v at idle and ~24v at 3/4 throttle. what i want to know is ~24v is way to high to charge a battery right? it should be regulated down to max ~14v? or is that just for cars? or is the little outboard just not that advanced and just charges at whatever it likes?

[Cool1]

Depends what outboard it is and what kind of regulator it has.
Being only a small 25hp you will find that it will only charge at a max of 4amps anyway. So once you connect the battery it will pull that 24v down.

[cri_ag]

ok so i connect it up to the battery the way i think it goes and then measure it? to measure amps i need to put my multimeter in series with the charge wire, correct?

[Cool1]

Yep connect the wires to the battery the way you think they go and then measure the terminal voltage. It shouldnt be much higher than 14v.
If that is all good connect your multimeter in series with the positive wire and see what the current flow is. I wouldnt expect it to be much at all.

[cri_ag]

excelent thanks for that
+ve rep!

[Cool1]

So did it work, or have you not tried it yet?

[cri_ag]

doing it as i type this, il post when i start it up

[cri_ag]

ok i started it and checked the voltage coming out of the alternator at idle it was 8-10v, so then i connected the charge wires to the battery with my mutimeter connected to the battery so i could observe any diference in voltage but i got nothing? the battery just puts out 11.2v regardless of engine rpm?

[74ROLLA]

Most small engine alternators run a magneto type charging system. In that size engine, they can put out 30 Volts AC, before being regulated back to a DC current, which then should (once connected) give you around 13.3 to 14.4 volts at the battery.

The regulator must be connected to a 12V battery to work, and the battery must have at least 8V (if jump starting) for the regulator to work

[Cool1]

ok i started it and checked the voltage coming out of the alternator at idle it was 8-10v, so then i connected the charge wires to the battery with my mutimeter connected to the battery so i could observe any diference in voltage but i got nothing? the battery just puts out 11.2v regardless of engine rpm?

Whats the terminal voltage of the battery without anything connected?
When you did connect the wires did you measure the current?

[cri_ag]

the teminal voltage of the battery with nothing connected is 11.2v
it dident register any current (= amps right?)

Most small engine alternators run a magneto type charging system. In that size engine, they can put out 30 Volts AC, before being regulated back to a DC current, which then should (once connected) give you around 13.3 to 14.4 volts at the battery.

so maybe ive picked the wrong wire? i think it does have the magneto type, ill take a pic

[cri_ag]

in the pic i used the red wire with the black fuse holder as the positive charge wire. there was another loose wire (cant see it in the pic) that i had a vauge recolection of being the negative charging wire maybe this is where im wrong? would it work if i just wired it (negative) to an earth (like you would a car?)

http://users.tpg.com.au/haack6/IMG_0023.jpg

sorry about the massive pic.

[Cool1]

That little black square thing in the top right is the rectumfire!
The 2? green wires that connect to it will be the AC input and the red wire will be the DC output.
The red wire will connect to the positive terminal of the battery, and the negitive terminal of the battery you can connect to any decent ground on the engine.
In that picture down the bottom I see a black wire in a blue crimp connector, where does that lead to? Looks like a nice ground wire to me

[Cool1]

For interest sake, whats the rating of the fuse?

[74ROLLA]

in the pic i used the red wire with the black fuse holder as the positive charge wire. there was another loose wire (cant see it in the pic) that i had a vauge recolection of being the negative charging wire maybe this is where im wrong? would it work if i just wired it (negative) to an earth (like you would a car?)

Going by the picture, (yes it is big - especially on dial up! lol) Two green wires come from the alternator as AC power into the regulator. These are then rectified and regulated to produce one red output DC charging wire, and the black wire earths the regulator. There should only be the red wire from there that goes on to either:

1) Positive side of battery
2) Battery side terminal of starter solenoid

The earth runs through the block:
Charging circuits do not have a negative black wire. (the wire not shown in the picture)
My guess is this would possibly be an accessory wire for running either a gauge or a light?

NB: disclaimer: check if any current etc first with multimeter before doing anything with this extra black wire!