Charging voltage from Merc 20 HP outboard.

[JDCAVE]

The charging voltage from my Merc 20 outboard on my skiff is 15.11 VDC. Does that sound too high? I am troubleshooting the display on my Hummingbird Depth sounder. The screen goes black when the engine is on. The sounder is connected to the start battery. This was a problem that started for the first time last summer. Googling the problem suggests that the voltage may be too high. It sounds like a solution is to remove the ES from the starter battery. That means a dedicated battery for the unit. The problem started last summer. I’ve confirmed that the voltage voltage going into the unit is the same as at the start battery.

How To Troubleshoot Depth Sounders And Fish Finders - BoatUS Magazine

The Merc 20 uses a stator for charging.

 

[john61ct]

Yes too high.

Workaround would be to put a 12V DC-DC buck converter that outputs a stabilized 13.8V between the engine+battery and the loads.

A proper DCDC charger to protect the battery would not be worth the cost.

Best of course to get the problem fixed at source if possible.

 

[DavidM]

You measure 15.11 V at the battery terminals? If so, it should be boiling electrolyte out fairly quickly from your battery.

My guess is that there isn't anything you can do to reduce the output from the O/B. It is often very poorly regulated.

David

 

[Ski in NC]

Little outboards often set the regulator voltage on the high side as they often do short runs and batts can get flat with a normal voltage.

Regulator might be faulty. Some don't even have regulators, just rectifiers.

If it is a regulator, one fix is to get an alternator diode and put it on regulator output before it goes to B+ cable terminal under the hood. It will drop your volts by 0.5-0.7Vdc and get your batt volts to a happy spot. This won't work if it is a rectifier.

 

[JDCAVE]

Thanks guys. I think I’ll call the local Merc distributor to see if a rectifier/regulator part be swapped out. Yes, DJ: 15.11 at the battery terminal and 15.11 out of the connection to the echo sounder.

This battery was fully charged, having come off of a 3 stage Promariner charger.

 

[motion30]

Many of the small outboard motors have no regulator at all just a simple diode unit to change the voltage to DC. An experience Merc Tech will know a regulator off another motor that will work

 

[Ski in NC]

Another fix is to go with a half charged batt.

Really.

 

[JDCAVE]

Yes too high.

Workaround would be to put a 12V DC-DC buck converter that outputs a stabilized 13.8V between the engine+battery and the loads.

A proper DCDC charger to protect the battery would not be worth the cost.

Best of course to get the problem fixed at source if possible.

I’m going to look at fixing it on the outboard end of things if I can. The buck converters I’ve seen don’t look like they could handle the outside marine environment.

Another fix is to go with a half charged batt.

Really.

Chuckle! Yes.

 

[Ka_sea_ta]

you could just add 3 appropriate amperage diodes in series to the positive feed of the DS

 

[JDCAVE]

you could just add 3 appropriate amperage diodes in series to the positive feed of the DS

Interesting, but would you please expand on this approach for this neophyte. Amperage or voltage?

Jim

 

[JDCAVE]

Further to this, the Hummingbird 160 manual indicates it automatically shuts down at >20 VDC, so seems 15.11 volts is within specs.

 

[Ka_sea_ta]

Interesting, but would you please expand on this approach for this neophyte. Amperage or voltage?

Jim

Look at the DS manual to find the amperage draw probably not more then a couple of amps. https://www.amazon.com/VNDEFUL-Mold...e=UTF8&qid=1522608994&sr=8-14&keywords=diodes These are overkill but would work. connect them in series with the white stripe end toward the DS. 3 in series will drop the voltage by a little 2 volts so the 15 volts goes to 13...

 

[kchace]

Look at the DS manual to find the amperage draw probably not more then a couple of amps. https://www.amazon.com/VNDEFUL-Mold...e=UTF8&qid=1522608994&sr=8-14&keywords=diodes These are overkill but would work. connect them in series with the white stripe end toward the DS. 3 in series will drop the voltage by a little 2 volts so the 15 volts goes to 13...

This absolutely will work. Just put 3, maybe 5 amp diodes in series between the battery and the DS.

Ken