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Discussion Starter · #1 ·
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?
 

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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.
 

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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.
 

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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.
 

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

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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.
 

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Discussion Starter · #9 ·
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
 

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Windy...I have charts from a very well respected mfr. that show far less difference between 30% an 50% discharge for THREE different ranges of batteries....
Cycles 4200>>>3200
1707>>>1280
768>>>576

That is the difference in cycle life between 30 and 50% discharge on their good/better/Best batteries. The important thing to note is that in each case in terms of AMP HOURS delivered over the life of the battery...cycling to 50% gives you more than cycling to 30%.
This is NOT the case with your last graphic nor does it resemble anything else I have seen. Are you at liberty to share the source and type of battery that was being tested in your above post?
 

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Windy...I have charts from a very well respected mfr. that show far less difference between 30% an 50% discharge for THREE different ranges of batteries....
Cycles 4200>>>3200
1707>>>1280
768>>>576

That is the difference in cycle life between 30 and 50% discharge on their good/better/Best batteries. The important thing to note is that in each case in terms of AMP HOURS delivered over the life of the battery...cycling to 50% gives you more than cycling to 30%.
This is NOT the case with your last graphic nor does it resemble anything else I have seen. Are you at liberty to share the source and type of battery that was being tested in your above post?
Hey Cam, it came from here ...

Source: 12 Volt Electrics in A'van for Manins
 

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I would scrap the small starting battery and just go with a single deep cycle battery. With an outboard, you can start by pulling manually if the battery is low. I sailed for years on Pearson 26 with a 8hp Johnson that charged a group 24 deep cycle house battery. It kept the charge up with no problem on cruises as long as three weeks.
 

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Why don't you

Why dont you just do away with the little motorcycle battery, and run off the house bank entirely. That little outboard isn't going to take enough out of a deep cycle house battery to effect it much. Will eliminate a battery, some wiring and simplify things too.
 
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