Do I need a new rectifier/regulator?

[LagunaJay]

My Yamaha 8HP outboard has a stock rectifier/regulator installed downstream of the lighting coil that produces 12.9V DC at idle power and 14.6V at mid-range RPM and higher. Don Casey (who I respect a lot) says anything above 14.4V indicates a defective regulator that is damaging the batteries, but I am hesitant to remove & replace because:

1) I don’t know the tolerance of the the installed voltmeter and maybe actual system voltage is less than 14.6V

2) The outboard‘s coil/rectifier only produces 6 amps max, and that’s at 5000 RPM, which I never run the engine at.

3) My battery bank consists of three large AGM batteries wired in parallel, so that’s a lot of capacity to absorb any excess voltage/current

4) I can’t actually find specs for Yamaha’s rectifier/regulator so maybe it’s actually operating correctly.

Any advice is appreciated.

P.S. Why isn’t the wire running to the starter motor protected with a fuse, fusible link, or some kind of current limiting device? My starter motor is wired through the #2 position of my battery switch, so I can de-power it if needed, but it seems the wiring on such a high draw circuit should be protected.

 

[dlochner]

1) I don’t know the tolerance of the the installed voltmeter and maybe actual system voltage is less than 14.6V

Use a digital multimeter to measure the voltage at the battery, not the installed voltmeter.

3) My battery bank consists of three large AGM batteries wired in parallel, so that’s a lot of capacity to absorb any excess voltage/current

Do you have a battery charger too, or are you relying on the outboard to charge the AGM batteries. AGMs do not fare well with partial state of charge.

P.S. Why isn’t the wire running to the starter motor protected with a fuse, fusible link, or some kind of current limiting device? My starter motor is wired through the #2 position of my battery switch, so I can de-power it if needed, but it seems the wiring on such a high draw circuit should be protected.

ABYC doesn't require it. A fuse can be added it just needs to be large enough to both protect the wire and provide enough current to start the motor. Starters have a large inrush of current which will blow some fuses, however it only lasts for a few milliseconds, once the motor is spinning the current draw drops and then it only lasts a few seconds until the motor starts.

 

[Whatfiero1]

I would start by cleaning all connections and getting a second meter with DC amp clamp especially check ground connections retest including amps output

 

[jviss]

I assume the Yamaha regulator isn't a smart, 3-stage charging regulator. If that's the case, then an output voltage of 14.6V is something of a mixed blessing, since if your bank is fully charged it's too much, but if it's not, it could be just right; chances are your batteries' recommended Acceptance stage voltage is pretty close to 14.6V.

You should check the battery data sheet to find the recommended acceptance stage voltage.

You should also verify that the regulator isn't a smart regulator.

 

[jssailem]

My battery bank consists of three large AGM batteries wired in parallel, so that’s a lot of capacity to absorb any excess voltage/current

This is not enough info to begin to answer the question.

Identifying the complete battery/charging system is the first step.

Starting at the "8HP outboard" producing "6 AMPs at 5000 RPM which I never run".

Assuming you have just 1 AGM Group 31 battery (a large AGM battery) with 100 amp hour capacity. You have run the radio, the lights, and maybe some other appliances enjoying your night on the boat. The battery is now at a 50% STATE OF CHARGE. You consumed 50 AMP hours and you need to replace them. At 6 amps which you "never run" you would need to run the outboard for 8.33 hours at full throttle producing 6 amps an hour, to begin to replace the energy you consumed.

I do not think it much matters whether the outboard regulator is producing 14.6 volts or not. You'll never run the outboard long enough or at a high enough RPM to do much more than tickle 1 battery let alone 3.

Here is the data sheet on Trojan Group 1 Batteries. It shows the info you need to identify your battery charging requirements.

https://www.trojanbattery.com/pdf/datasheets/31AGM_Trojan_Data_Sheets.pdf

 

[LagunaJay]

Use a digital multimeter to measure the voltage at the battery, not the installed voltmeter.



Do you have a battery charger too, or are you relying on the outboard to charge the AGM batteries. AGMs do not fare well with partial state of charge.



ABYC doesn't require it. A fuse can be added it just needs to be large enough to both protect the wire and provide enough current to start the motor. Starters have a large inrush of current which will blow some fuses, however it only lasts for a few milliseconds, once the motor is spinning the current draw drops and then it only lasts a few seconds until the motor starts.

Thanks for the reply DL. Yes, I also have a battery charger that keeps the batteries fully charged when hooked to shore power. Good idea to use my multimeter to double check the installed voltmeter; I will do that next time I run the engine.

 

[LagunaJay]

NOTE: I found an article on WestMarine’s website that says 14.7V is the recommended charging voltage for AGM batteries, so I am not nearly as worried now that the outboard’s alternator/rectifier is going to cook my batteries on an extended day of motor cruising.

Choosing a Battery Charger for your Boat | West Marine

 

[LagunaJay]

Use a digital multimeter to measure the voltage at the battery, not the installed voltmeter.

Thanks Dave. I checked voltage at the battery with a multimeter while the engine was running and the voltmeter matches battery voltage exactly, so that was a good cross check and a good suggestion on your part. I ran the engine for 10 minutes at mid-RPM and the voltage gradually increased to 14.7V and stayed there, so I think the motor’s regulator has a generic bulk charging profile; 14.7 volts is recommended absorption voltage for AGM batteries (according to WestMarine) so I’m comfortable now that the batteries are being charged correctly. The shorepower battery charger will be doing most of the charging work, but it’s nice to know if I’m out motoring extensively that the batteries won’t be damaged. Thanks for your help.

Do you have a battery charger too, or are you relying on the outboard to charge the AGM batteries. AGMs do not fare well with partial state of charge.



ABYC doesn't require it. A fuse can be added it just needs to be large enough to both protect the wire and provide enough current to start the motor. Starters have a large inrush of current which will blow some fuses, however it only lasts for a few milliseconds, once the motor is spinning the current draw drops and then it only lasts a few seconds until the motor starts.