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Yamaha charging alternatives

svamelia

New member
"Here's one for the more m

"Here's one for the more mathematically/electrically inclined.

I have a Yamaha 9.9hp 4-stroke electric start as our main engine. I want to be able to continue to charge the starter battery as needed and then via an A/B switch, trickle charge the house batteries.

The Yamaha ignition system is AC with a rectifier, not an alternator. There is no regulator. The battery leads from then engine outputs 13 amps DC at a minimum 13.5 volts, thus producing 175 watts. This being the case, I want to make sure I don't over-cook the house battery bank with 13a when only a 2a float charge is required.

As silly as it may sound, I'm toying with the idea of simply connecting a 150 watt, 240v inverter to the 13 amp 13.5v engine output to run my 240v shore-power battery trickle charger. In essence, I would be using the 240v inverter as a regulator between the engine and the batteries.

My shore power charger 240v mains supply specs:
Charging at:
2a draws 0.16a off the mains,
4a draws 0.26a
8a draws 0.51a
16a draws 1.04a

As long as I set it to only a 2a charge, a 150w inverter should be more than enough. Indeed, an 8a charge would only require 122 watts.

My question is; while motoring, would I be able to do a 2a trickle charge from the 240v mains charger (which requires 38.4 watts) using a 150w 12v inverter which supplies the 240v?

I'm sure I'm missing something obvious here, or my math is wrong, but if it works, it would enable a more stable charging environment for the house batteries.

The 240v mains (shore power) charger automatically and constantly adjusts its output to maintain the proper charge and gives a nice digital readout of amps, volts and percentage of overall charge status. Also it would be nice to leave everything connected when we simply want to re-plug into shore power again.

You might ask why I would NEED to use this method rather than charging directly off the motor. Well...

The "alternator" on the Yamaha 9.9 is actually just made up of a couple of coils under the flywheel that generate AC into a rectifier assembly when a magnet in the flywheel passes by. A pretty blunt instrument indeed. You would have to get into the motor's guts to find a way to reduce the charge voltage.

The problem is that I can't merely reduce the maximum output voltage, as that will also cut output at lower RPM's. What happens is that when the batteries are getting near full charge, the voltage starts creeping upwards, and can reach 16 or 17 volts, which is hard on the house battery.

I have to constantly monitor charging voltage and when it gets above 14.7 volts, I have to turn on the cabin lights, etc. to get the voltage lower. That's really not satisfactory. The owners manual recommends buying an optional regulator from my Yamaha dealer for just this situation, but no dealer globally seems to be aware of its existence.

The cables from the engine to the battery are used for both supplying power to the starter, and then to provide charging to the batteries. I need to limit the charge voltage to 14.7 volts, and whatever rectifier/regulator is built into the motor doesn't do that.

I tried asking Yamaha, since they vaguely mention the existence of such an animal in the literature that came with the motor. After going in circles between the company, and the numerous dealers they referred me to, nobody has a clue. I've come to the conclusion that Yamaha had the intention of producing such an option but never got around to actually releasing one.

I have found some regulators designed for solar panels, but they don't take into account supplying heavy (100 amps!) current back to the starter motor.

Thus is my predicament when it comes to safely charging the house (other than using a separate on-deck generator, or going totally solar)."
 
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