Voltage Regulation: 1980 115 Tower of Power:

[Old Merc Man]

Completing a full restoration of an aluminum Smoker Craft Magnum 162. All plywood replaced, floor, transom (two layers) and gunwales with 3/4"marine plywood. My concern now is my 115 Mercury with CDI ignition probably has unregulated charging to the battery. The boat has two Interstate 31MHD batteries, one is specifically a house battery servicing only the engine and ignition. I called Interstate to determine if that battery was vented to the atmosphere and the employee said it was. I'm not absolutely convinced. There are no visible caps, one long plate with an oval opening on the edge in the middle. Perhaps a location for a cap removal tool, he said it serves as a vent also. Yesterday I installed a Voltage Gauge to monitor the charging. I don't want to blow up the battery or reduce it's working life and am wondering if it's feasible to install a voltage regulator (CDI markets them) or just hook up something else to the battery to draw off excessive electrical charge. The CDI unit looks like it would alleviate my worries but installation is probably above my pay grade. Your advice is greatly appreciated.

[luv2gofast]

Completing a full restoration of an aluminum Smoker Craft Magnum 162. All plywood replaced, floor, transom (two layers) and gunwales with 3/4"marine plywood. My concern now is my 115 Mercury with CDI ignition probably has unregulated charging to the battery. The boat has two Interstate 31MHD batteries, one is specifically a house battery servicing only the engine and ignition. I called Interstate to determine if that battery was vented to the atmosphere and the employee said it was. I'm not absolutely convinced. There are no visible caps, one long plate with an oval opening on the edge in the middle. Perhaps a location for a cap removal tool, he said it serves as a vent also. Yesterday I installed a Voltage Gauge to monitor the charging. I don't want to blow up the battery or reduce it's working life and am wondering if it's feasible to install a voltage regulator (CDI markets them) or just hook up something else to the battery to draw off excessive electrical charge. The CDI unit looks like it would alleviate my worries but installation is probably above my pay grade. Your advice is greatly appreciated.

A regulator should not be necessary. Mercury only used them on fuel injected motors to protect the ECU. The charging system doesn't put out enough current to hurt the battery and it sounds like those are wet batteries and the oval opening is a vent. If you check voltage across the battery while running I doubt you will see > 14.5v. Any 12v automotive/marine equipment should be fine with 14.5v.

[rgsauger]

X2. Double check voltage with a multimeter at 2000 rpm. If under 14.7 or so, you're fine

[Old Merc Man]

I successfully water tested the old 1980 115 Mercury. She topped out at 41 mph @ 5600 rpm. I glanced down at the Voltage gauge while under full power and the gauge was showing an amazing (to me) 18 Volts. I didn't notice the voltage under reduced throttle. I won't be frequently pushing the old girl at maximum throttle, it ran well at 4500 rpm and still pushed the boat at a respectable clip. So apparently the charging system is in good working order. Just following up on my thread.

[rgsauger]

18V is WAY too much! That will kill electronics and such, too.

For me, I used something like this when I replaced my burned up water cooled regulator. So far, has worked great. 14.2V at 6000 RPM

https://www.ebay.com/itm/New-Voltage...AAAOSwNw1d0mP-

$20 and 5 yr warranty

[rgsauger]

Your boat looks great, by the way. Outstanding job on your resto

[Old Merc Man]

Thank you rgsauer. The motor's battery is independent from all the other circuitry. Over charging a battery never produces good results. I'll research retro fitting something.

[Old Merc Man]

One more photo. The only remaining bit of work though not essential is replacing the carpet on the top of the gunwales. I don't want to remove the rub rail, way too many rivets to rattle around inside the gunwale trapped by the foam . Perhaps a good surface prep, aluminum primer and a nice top coat of paint or non skid application.

[Flatlander]

Thank you rgsauer. The motor's battery is independent from all the other circuitry. Over charging a battery never produces good results. I'll research retro fitting something.

I used to run an mid 80's 115 (newer version with switch boxes) on my Switzer. I ran it hard and it would boil the battery until I added a voltage regulator. I believe I just used a regulator off a V6....

[Dave Strong]

I successfully water tested the old 1980 115 Mercury. She topped out at 41 mph @ 5600 rpm. I glanced down at the Voltage gauge while under full power and the gauge was showing an amazing (to me) 18 Volts. I didn't notice the voltage under reduced throttle. I won't be frequently pushing the old girl at maximum throttle, it ran well at 4500 rpm and still pushed the boat at a respectable clip. So apparently the charging system is in good working order. Just following up on my thread.

AGM battery?

Dave

[Old Merc Man]

No Dave, not recommended, need wet cell for the old inlines. The boat is set up with two Interstate 31MHD batteries. One is for the motor and it's power tilt & trim motor exclusively. I need to figure out the proper installation for a voltage regulator, they weren't equipped with them back in the day. Wiring one up is beyond my pay scale. I'll give CDI a call when the budget allows it. Their units aren't cheap by any means. rgsauger chimed in with an inexpensive alternative in his post above. I appreciate the help. 41mph @ 5600rpm seems to be the correct numbers for that motor and a 17 pitch prop. Thank you, Bruce

[Dave Strong]

No Dave, not recommended, need wet cell for the old inlines. The boat is set up with two Interstate 31MHD batteries. One is for the motor and it's power tilt & trim motor exclusively. I need to figure out the proper installation for a voltage regulator, they weren't equipped with them back in the day. Wiring one up is beyond my pay scale. I'll give CDI a call when the budget allows it. Their units aren't cheap by any means. rgsauger chimed in with an inexpensive alternative in his post above. I appreciate the help. 41mph @ 5600rpm seems to be the correct numbers for that motor and a 17 pitch prop. Thank you, Bruce

You don't need 2 batteries, just run one 24 series and bet its fine. Thats all they were designed yo run.

Dave

[luv2gofast]

You don't need 2 batteries, just run one 24 series and bet its fine. Thats all they were designed yo run.

Dave

I agree with Dave, they have been running that way for many, many years. Your batteries are "wet" cells and the oval thing is a vent for sure. Wet batteries can tolerate a much higher voltage than the more modern AGM or for gel. It is possible that some electronics may not be rated for > 14.5 volts but if it is designed for automotive use (marine use) it should be protected against the 18 volts you are seeing, especially for short periods of time. As I said before, Mercury didn't put voltage regulators on engines until they switched to electronic fuel injection. You could easily add the regulator that was on the 220 laser motors as it was just a shunt regulator that grounded any voltage over about 14.5. It only has two terminals and goes between the + and ground but it's not necessary for the battery.