Small outboard electrical output?

[massnspace]

I have a Tohatsu 9.8 outboard on a small sailboat. Electric start, and rectifier regulator to recharge battery.

When the motor is on full rpm., my digital volt meter in the boat jumps from the current battery voltage (say 12.3, for example) up to about 12.8. Yes, it charges the battery, but slowly.

But I saw a video recently of a guy running a Yamaha 8 hp and the voltage said 14.4 when he revved it.

So. Should I be getting over 14 volts when the motor is revving high? This is NOT an alternator, just a rectifier.

[Tin Tin]

Attach a multimeter directly to the battery terminals and test when engine is running or switch everything else off like depth sounder fridge etc

[Adelie]

The voltage probably corresponds to the battery bank’s state of charge. If the bank was clos to full it would probably be reading higher.

[rslifkin]

As mentioned, your batteries are likely not fully charged, so the output from the engine isn't enough to raise the voltage up to the regulator's target voltage.

[thinwater]

Small electric start outboards on small sailboats are notorious for not providing enough charging. Between starting and self-discharge, the 10 minutes they run at less than full rpm might provide 1/2 Ah of charging. Self-discharge of a starting battery might be 3.5 Ah per month. If you only take it our 1-2 times per month, the charge gradually goes down. On the other hand, if it is a power boat and you run it hard for an hour each time, then you have charged several Ah and the battery stays up.


You need to either charge the batter or add a small solar panel and controller. Without regular charging to full the battery will suffer from partial SOC and die young. This is why I have a small solar panel on my F-24 MKI. Just battery maintenance.

[massnspace]

Originally Posted by thinwater

Small electric start outboards on small sailboats are notorious for not providing enough charging. Between starting and self-discharge, the 10 minutes they run at less than full rpm might provide 1/2 Ah of charging. Self-discharge of a starting battery might be 3.5 Ah per month. If you only take it our 1-2 times per month, the charge gradually goes down. On the other hand, if it is a power boat and you run it hard for an hour each time, then you have charged several Ah and the battery stays up.


You need to either charge the batter or add a small solar panel and controller. Without regular charging to full the battery will suffer from partial SOC and die young. This is why I have a small solar panel on my F-24 MKI. Just battery maintenance.

We run out motor, on average, many hours a day. We travel far distances way off in the islands of the Salish Sea.

And yes, it does work. It charges.

But why does the voltage meter of the panel never go to 14.4 volts? That’s my question…..should it go right up there as soon as the motor is on full RPM?

[massnspace]

Originally Posted by rslifkin

As mentioned, your batteries are likely not fully charged, so the output from the engine isn't enough to raise the voltage up to the regulator's target voltage.

Even when the battery is fully charged (first hour of any trip after charging the battery fully at home), it doesn’t read anything near 14.4. Just something like 12.8.

Should it be 14.4?

[Jammer]

Originally Posted by massnspace

I have a Tohatsu 9.8 outboard on a small sailboat. Electric start, and rectifier regulator to recharge battery.

When the motor is on full rpm., my digital volt meter in the boat jumps from the current battery voltage (say 12.3, for example) up to about 12.8. Yes, it charges the battery, but slowly.

You have to measure the current (amperage) to answer the question. Small outboards should deliver 6-12 amps at cruise, depending on the specific make, model, and year.

If you do not have one, I would suggest purchasing a DC clamp-on ammeter. I have one and it's been an extraordinarily valuable tool for electrical troubleshooting. Shop carefully as most clamp-on ammeters are AC only for current but have a DC setting for voltage.

https://www.amazon.com/Fluke-301D-ES.../dp/B0DGY7GT82

If measurement shows a reasonable amount of current, then the outboard is doing its job, and the low voltage may be explained by a deeply discharged battery, a shorted cell in the battery, or a heavy DC load.

This is NOT an alternator, just a rectifier.

The terminology is confusing because these motors have a small alternator winding that provides power to the electronic ignition system. The rotor is formed by a permanent magnet on the flywheel, similar to a magneto. An adjoining winding is connected to a rectifier to provide modest battery charging ability from the same rotor.

[thinwater]

a. Put a clamp-on ammeter on it when the battery is low. That will tell you output.


b. Voltage depends on temperature, charging amps, and SOC. The Salish Sea is not a warm place. Many parts to the puzzle. In fact, for a small charging source in a cool climate, 14.4 V is pretty high. 13.something would be more normal with a small motor and group 24 battery.