Starting battery and deep cycle - charging

[ChesapeakeCal29]

i have a 9hp outboard that has electric start and a alternator. it has a motorcycle battery that is dedicated for starting. it is not hooked up to the main panel. it's a nissan 9.8 and i do not believe the output voltage is regulated.

What i would like to do is charge my deep cycle battery while the motor is running.

what is the best way to accomplish this?

could i just wire them together in parallel?

is there a regulator device that completes the circuit when a charging voltage is present?

[wind_magic]

Originally Posted by ChesapeakeCal29

i have a 9hp outboard that has electric start and a alternator. it has a motorcycle battery that is dedicated for starting. it is not hooked up to the main panel. it's a nissan 9.8 and i do not believe the output voltage is regulated.

What i would like to do is charge my deep cycle battery while the motor is running.

what is the best way to accomplish this?

could i just wire them together in parallel?

is there a regulator device that completes the circuit when a charging voltage is present?

Take a look at the "Combiner question" thread on this same sub-forum, it talks about the devices you would want to do what you want to do. Basically a device that keeps your start battery charged and charges your deep cycle battery with whatever is left over.

[ChesapeakeCal29]

thanks, looking for something cheaper than $215. could i get some FET switch than open at 13.5 volts or something at radio shack?

[wind_magic]

Originally Posted by ChesapeakeCal29

thanks, looking for something cheaper than $215. could i get some FET switch than open at 13.5 volts or something at radio shack?

Hmm, well, sure, I could build something out of a 0.30$us PIC processor, a resistor, a transistor, a 5vdc voltage regulator, a diode, and a relay that would allow you set your "trip points" and connect the two battery banks via a diode when they are hit, so yes it can be done inexpensively - but I suspect you wouldn't be asking if you knew how. Edit - and more importantly, the tools to do it would cost more than just buying the device if you didn't have a PIC programmer.

[wind_magic]

Looks like someone made something similar into a kit for automobile sensors - AutoSpeed - The Simple Voltage Switch, except theirs has a pot in it so you can adjust the trip trigger without reprogramming the processor.

[wind_magic]

ChesapeakeCal29,

You could probably get a 14v zener diode and use that to switch a relay with a simple circuit. Actually here I just found someone who is going in the right direction, maybe you could use this as a starting point - An Amplified Zener, they are using the zener to create the trip and then switching a transistor.

[sailingdog]

The Blue Sea ACR 7160 is only about $82 or so. Marinized and well worth it.

[camaraderie]

Umm...the alternator is 6 amp. MAX...less at less than full throttle. Let's say you had 100% output...unlikely...and a 100amp house battery that was 50% discharged. If you ran the engine at full throttle for 8 hours you would nearly be fully charged. The reality is that you do NOT have six amps, that some of what you do have will be lost in conversion, and you will probably have to motor for 12 hours to fully charge a 1/2 discharged battery.
This is a poor idea from the get go. Get a honda1000 to charge the battery or something similar.

[ChesapeakeCal29]

Thanks for all the comments!

i think i will just get a switch and throw it on during motoring if the house battery drops below 11 volts or so. i have a solar thats always on too, and sail about 15 times a year, thanks for the advice! cheers

[wind_magic]

Originally Posted by ChesapeakeCal29

Thanks for all the comments!

i think i will just get a switch and throw it on during motoring if the house battery drops below 11 volts or so. i have a solar thats always on too, and sail about 15 times a year, thanks for the advice! cheers

Nice solution, I like it.