1980 70HP low charging voltage

[djeady]

I have a 1980 70 HP Evinrude that is probably the best running 3 cylinder OMC I have ever had, however my battery keeps getting run down.

I've checked the stator and the rectifier, and they seem fine although there is a bit of resistance (200 ohms) one way on the rectifier (infinite the other way of course). I've cleaned all contacts from back to front.

When the boat starts, the voltage gradually climbs - for example if it starts out at 12.2 it will gradually at a rate of .1 volt every 3-5 minutes, but it never seems to get above 12.5. The voltage does not increase with motor RPMs.

I don't know if it's related or not, but this motor also regularly blows its main fuse - there are no accessories to speak of (lights and a bilge pump).

I'm scratching my head on this one - can anyone help?

 

[wilde1j]

Re: 1980 70HP low charging voltage

Measure voltage across battery terminals with a decent DVOM. You should get at least > 13 VDC. If not, you are not charging. Check all terminations for tight, bright and clean. If still no good, check AC voltage from stator, typically a yellow pair. Should get > 16 to 18 VAC, although I don't have a shop manual for your motor. If AC is there, rectifier is bad.

Also, you may have a bad battery. Have it load tested after a good charging.

If the motor 20 A fuse blows regularly, you have a short somewhere. You will need an electrical diagram, which is in a shop manual.

BTW, why do you think the stator and rectifier are good?

Welcome to iboats!

 

[djeady]

Re: 1980 70HP low charging voltage

Thanks for the response.

I tested the stator and rectifier per the manual - stator has low resistance across connectors and infinite to ground. Rectifier has infinite resistance one way and very low resistance (but not zero) the other way.

I will try testing the voltage across the stator leads.

As I send in my original post, all connections have been cleaned thoroughly.

 

[djeady]

Re: 1980 70HP low charging voltage

Ok, checked stator voltage - starts out at 35-36 VAC at idle and goes up to 50+ with the engine speed.

Must be the rectifier.

I would also explain why my tach stopped working - thought that was just a wiring issue.

I'll hunt down a rectifier and report back.

 

[wilde1j]

Re: 1980 70HP low charging voltage

If the tach isn't working it IS the rectifier.

 

[djeady]

Re: 1980 70HP low charging voltage

Hmm, replaced the rectifier and now I get about 13V at idle and it goes up to about 13.5 at speed - still seems low.

Tach is still not working, but that may not be related.

Should I be getting more voltage or is this acceptable.

 

[wilde1j]

Re: 1980 70HP low charging voltage

Did you charge the battery beforehand? BTW, what accessories were on. You probably have a 6 or 9A alternator, which isn't much. 13V is less than I would expect, but those low amp guys seem to take a while to increase voltage and 13.5 VDC is fine. The charging systems on old OB's are somewhat marginal, given most people's penchant for lots of electronic stuff. Since 12.7 VDC is a static, fully charged battery, your charging system is clearly working.

A word of caution, don't disconnect power stuff with a running motor, or reverse +/- leads, or you will be in for another rectifier.

The tach may be a bad tach, but I would make sure it's connected properly and pulse setting is correct for your motor.

 

[djeady]

Re: 1980 70HP low charging voltage

I did not charge the battery first and the battery is a bit weak - takes a charge but not enough to shut the charger off. Wanted to get the power problem resolved first.

So I'm guessing this is what I'll get - at least I'm seeing the voltage go up with RPMs now.

This is an old center console dusky - my only accessories are bow and stern lights and a bilge pump I added last year - boat was 30 years old and had never had a bilge pump!

I've check that there is not current draw when the motor is off and the ignition is on, so I don't think I'm losing anything.

I'll have a look at the tach - the wiring under the dash looks like it was done by a hungover spider, so may wind up redoing a lot of it.

Did you charge the battery beforehand? BTW, what accessories were on. You probably have a 6 or 9A alternator, which isn't much. 13V is less than I would expect, but those low amp guys seem to take a while to increase voltage and 13.5 VDC is fine. The charging systems on old OB's are somewhat marginal, given most people's penchant for lots of electronic stuff. Since 12.7 VDC is a static, fully charged battery, your charging system is clearly working.

A word of caution, don't disconnect power stuff with a running motor, or reverse +/- leads, or you will be in for another rectifier.

The tach may be a bad tach, but I would make sure it's connected properly and pulse setting is correct for your motor.

 

[djeady]

Re: 1980 70HP low charging voltage

I really appreciate all the help.

I'm cleaning up the wiring and I'm a wee bit confused by the tach wiring. There is a grey wire which is supposed to go to the alternator. Right now it's connected to a beige coloured wire which I can't find on my wiring diagram. I think it should go to the purple wire which goes to the ignition switch, then to the overheat buzzer - is this correct?

On the connector terminal on the motor, the bottom wire connector is labelled as purple although if it was purple it has faded to beige. This wire connects to the bottom terminal - there doesn't appear to be anything else connected to it which is also puzzling.

I think the main fuse problem was a result of most of the connectors on the ignition switch being lose, resulting in a short when I turned the key.

 

[wilde1j]

Re: 1980 70HP low charging voltage

The grey one rings a bell as the pulse lead, purple is a 12V + as I recall, tan is normally to/fr the hot horn and the overheat sensor on the motor.

You really need a wiring diagram for your motor, which I don't have. Perhaps someone here could scan one for you, if you're unable to get otherwise. The iboats website has shop manuals available as well. Maybe time to get one.

OK, I looked in my Etec book, and I think the color convention hasn't changed. It shows the following, which MAY be correct for you tach:

Black (grd) to tach GND terminal
Purple (+12V) to tach +12V terminal
Gray (pulse) to tach PUL terminal

Since many people may have messed with the boat's wiring, I would verify each all the from tach to the motor.

 

[djeady]

Re: 1980 70HP low charging voltage

I think I've got everything hooked up properly, but still no joy.

The one thing that bothers me is shouldn't there be something else connected to the bottom wire of the terminal strip other than just the grey wire - shouldn't it be jumpered to one of the inputs to the rectifier?

 

[wilde1j]

Re: 1980 70HP low charging voltage

If the grey is terminated to the correct place on the tach, and you've verified the +12V, which is switched, so the ig sw must be "on", and the ground at the tach, then I would verify the gray from the tach all the way back to the motor, and assuming the tach is good, it should work. If it doesn't then I would suspect the tach is, in fact, bad.

 

[djeady]

Re: 1980 70HP low charging voltage

Jim, I appreciate all your help.

I'm guessing the tach is toast - don't know how to test other than to use another tach. A tach on a single outboard boat really doesn't do a lot anyway, so I'm not concerned - thought I would try and fix it, but no big loss.

Definitely seems to be charging now and I cleaned up a lot of the wiring ang got familiar with most of it.

As far as the gray wire on the terminal strip on the motor, that one does not connect to anything, there is one further up that is bridged to the stator and I'm guessing that is the correct one.

I do have a wiring diagram - it just isn't the easiest thing to read.