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Old 11-03-2010, 04:15 PM
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12v/24v electrical stuff - wish Doc were here

This is sorta hotroddish since its for my hotrod boat

I have a 19' I/O boat that I occasionally use for fishing so I bought a 24v outdrive-mounted electric trolling motor. I can do it the old fashioned way that I know of... use three batteries- two in series for the electric motor and one separated for the rest of the boat, then disconnect them and use a charger. But that's a pain in the ***.

I found many 3-bank marine on-board chargers, but they are all 12v. Then I noticed today on our 24v car pusher at the shop, it has a Minn Kota 12v 3-bank charger on it. How does that work? How can a 12v charger charge two batteries that are wired in series for 24v?

I want it to be as plug-n-play as possible. Can I use two batteries and somehow source 12v from it to run the boat? Do I need three? Can I use an onboard 12v charger to charge them all? Can I recharge the 24v series batteries with the alternator?

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Old 11-03-2010, 05:16 PM
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For the sake of safety (as in not running the starting battery down with the trolling motor) I would never run only 2 batteries in your situation. But if you insist, here's how you can do it:



The multi-bank chargers are 12v per bank and get connected as illustrated above. One charger or bank per battery. A 3-bank can charge 3 batteries at once, which is typically used either for three batteries in a 36v series, or two in a 24v series plus one starting battery.

I see that MinnKota also sells 2-bank chargers which would be better suited to this application, or you could use two separate chargers.

There is no need to undo the series connections between the batteries when you charge them, just hook the charger(s) up as shown. The chargers don't 'care' if there is another battery upstream or downstream. The charger only charges the battery that is between it's + and - leads.

The main engine's alternator will only charge the first battery.

Hope this helps....
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Old 11-03-2010, 05:34 PM
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These chargers use diodes to isolate the batteries from one another.
The charger just directs power in one direction to the battery needing a charge.
Same with the alternator. You will also need a battery isolation device to charge the batteries with the alternator. See minn-kota mk-3-dc.

vicrod
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Old 11-03-2010, 06:01 PM
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An alternative would be to buy a series parallel switch. Years ago Kenworth semi trucks used a twenty four volt starter and the rest of the truck was wired for twelve volt including the alternator.

Like I said its been a while and even though I worked on plenty of them I would need to look at a diagram. I did a quick search and found this:
http://www.gonefcon.com/trucktcom/parallel_sw.htm
Maybe it will help. I think all you would have to do is put the trolling motor where the starter is in the diagram.
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Old 11-03-2010, 07:21 PM
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Im with JOE G that youd be "f"d if you only had 2 batts and drained both trolling and have nothing to start with. Sucks, but 3 is the most reliable. With relays you can have em all charge from the alternator when running the motor
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Old 11-04-2010, 02:27 PM
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Ok, its all making sense. The 12v charger works because you are hooking up three discreet 12v sources, but I can't just hook the alternator up to all of them because it would A) short the series to 12v, and B) not work

Not doubting you JoeG, but someone told me I can't get 12v the way you describe. Its not a big issue since I'll probably run three anyway for safety/starting, I was just concerned about weight.

Basically, what I want is a hands-off setup - I want to run the electric motor all I want, isolated from the 12v starting, have an onboard charger that I can plug in for situations where I don't get a full charge on the way back to the dock, and possibly allow the use of the series batteries to jump the 12v starting battery. Let me see if I can come up with my own diagram and you guys can complete it...

I had installed two batteries in a van for camping so I could drain the coach battery and still start it. I isolated them with a solenoid sorta like in this image. The solenoid was on a three way switch so it could be off all the time, only energized when the key was on, or on all the time for jumpstarts etc. This diagram is what I think would work, but it seems too easy. Seems like getting the common ground is necessary for jump starts, but also seems like it would short the series, or at least short the discreet charging circuits. If someone wants to edit/complete this image it would be great. I'm a visual kinda guy.

Ok, next step... how do I go about setting it up to charge all three batteries from the alternator?
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Old 11-04-2010, 08:02 PM
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Part of the deal w/trolling motors is they require deep cycle batteries to get the best performance and life from the batteries. A deep cycle trolling motor battery shouldn't be used as a starting battery and vice versa (obviously) so the two different types of batteries should be used for the best performance and life of the batteries anyway.

It would seem that by connecting the batteries in parallel while charging, the alternator would do the job, then you'd switch back to series for 24V use.

Last edited by cobalt327; 11-04-2010 at 08:09 PM.
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Old 11-04-2010, 08:09 PM
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Quote:
Originally Posted by Chris Kemp
An alternative would be to buy a series parallel switch. Years ago Kenworth semi trucks used a twenty four volt starter and the rest of the truck was wired for twelve volt including the alternator.

Like I said its been a while and even though I worked on plenty of them I would need to look at a diagram. I did a quick search and found this:
http://www.gonefcon.com/trucktcom/parallel_sw.htm
Maybe it will help. I think all you would have to do is put the trolling motor where the starter is in the diagram.
I'm not quite sure that the series/parallel switch on the Kenworth trucks is rated for constant duty . I honestly doubt that it has low draw hold in windings and would probably overheat . But that is just my opinion and I am always open to be corrected .
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Old 11-05-2010, 08:09 AM
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Quote:
Originally Posted by cobalt327
Part of the deal w/trolling motors is they require deep cycle batteries to get the best performance and life from the batteries. A deep cycle trolling motor battery shouldn't be used as a starting battery and vice versa (obviously) so the two different types of batteries should be used for the best performance and life of the batteries anyway.
Correct. I would use two deep cycles for the 24v and one marine starting for the rest. I don't need a full deep cycle for the boat, but there are many times when I anchor and fish for a few hours with the fish finder, marker lights, and running the electric anchor winch.

Quote:
It would seem that by connecting the batteries in parallel while charging, the alternator would do the job, then you'd switch back to series for 24V use.
I agree, but simplicity of operation is key. I don't mind complex wiring and a little extra money to get it how I want it.

The thing is, if I'm anchored, I will be using the 12v system alot... usually not enough to prevent starting after a few hours but if I'm in a good fishing hole the 12v accessories sometimes drains enough juice that the 9.5:1 350 is a little slow to crank. If I'm using the electric to troll, the 12v will be fine, but I would like to be able to at least partially recharge the 24v while I'm travelling up the lake to the next trolling spot. Getting to the batteries in this boat isn't easy. I can rig up a switch anywhere with some heavy wire and some elbow grease, but if I'm going to all that effort, might as well spend a little more cash and get the switches, relays, solenoids, etc, that I need to make it hands-off.

So, having a 24v source that can be charged with the alternator and jump the 12v when necessary is what I want... if it can be done without a lot of effort.
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Old 11-05-2010, 10:43 AM
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May Be Totally Screwed Up But .....

Here is quick drawing that I thought up. I may be totally screwed up in my thinking , but I thought I'd give it a shot .....Allan
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Old 11-05-2010, 11:07 AM
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adantessr... I like that. I can rig it up with two solenoids (one normally open, one normally closed... unless they make DPDT solenoids) so that its always 12v with the key on and always 24v with the key off. That should work. It removes the ability to do both at the same time... or at least the electric motor would operate slowly on 12v if the key is on.
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Old 11-05-2010, 11:32 AM
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I think I may have found a sorta solution...

Minn Kota charger

Minn Kota sells multi-bank chargers that either hook up to 120v OR 12v from the alternator. That link is for one that charges 3 banks from the alternator. So if I use that it will charge all three batteries while running. Then with a separate charger (either on board or separate) I should be able to hook it to the alternator wire and charge with a 120v charger letting the on-board charger box think the alternator is providing the juice. Then for the once or twice a year I need a jump start, I can disconnect the on-board box and throw a knife switch on the battery that connects ONE of the 24v bank batteries to the starter battery.

I was hoping to find an onboard charger that has inputs for both 120v and 12v but I haven't found that yet.

Here is my new diagram:
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Old 11-05-2010, 11:53 AM
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Quote:
Originally Posted by curtis73
I think I may have found a sorta solution...

Minn Kota charger

Minn Kota sells multi-bank chargers that either hook up to 120v OR 12v from the alternator. That link is for one that charges 3 banks from the alternator. So if I use that it will charge all three batteries while running. Then with a separate charger (either on board or separate) I should be able to hook it to the alternator wire and charge with a 120v charger letting the on-board charger box think the alternator is providing the juice. Then for the once or twice a year I need a jump start, I can disconnect the on-board box and throw a knife switch on the battery that connects ONE of the 24v bank batteries to the starter battery.

I was hoping to find an onboard charger that has inputs for both 120v and 12v but I haven't found that yet.

Here is my new diagram:
Hey Curtis , It looks like you've got it nailed there . I see no reason that won't work . I hope I helped stimulate your thinking a little bit . That's why we're all on here isn't it ? ...Allan .
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Old 11-05-2010, 12:01 PM
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adantessr
you may have it. kiss (keep it simple, stupid) works.
i'll study it some more, but i can't see an obvious flaw to your solution.

curtis
look for 12v golf cart solenoids, they are rated for continuous duty
vs a ford style solenoid that is rated intermittent duty

use a multi-position switch and a different position for charge, run and isolate
i add isolate because if you have dead deep cycle batteries you may want to isolate them
all 3 off would isolate; 2 on, 1 off for run 24v; 2 off, 1 on for charge


i use golf cart solenoids to run 12v winches
i pick them up on ebay for cheap

another thing you might want to look at is the effect of charging deep cycle betteries with an automotive alternator

Last edited by ogre; 11-05-2010 at 12:08 PM.
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Old 11-05-2010, 01:29 PM
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Quote:
Originally Posted by ogre
adantessr
curtis
look for 12v golf cart solenoids, they are rated for continuous duty
vs a ford style solenoid that is rated intermittent duty
What about diesel glow plug solenoids? I used one like that for my Van (see above) and it seemed to last.... but the golf cart solenoids sound like a beefy choice.

Quote:
use a multi-position switch and a different position for charge, run and isolate
i add isolate because if you have dead deep cycle batteries you may want to isolate them
all 3 off would isolate; 2 on, 1 off for run 24v; 2 off, 1 on for charge
not quite following you, but I'm not that good Are you suggesting a solution to my jumpstarting query, or is that just for help on charging isolation?

Quote:
another thing you might want to look at is the effect of charging deep cycle betteries with an automotive alternator
Typically its not an issue, especially with proper voltage regulation. I plan on digging a bit deeper with this one though. I'll probably use either a regular cranking battery or a marine starting battery for the 12v. If charging deep cycle batteries with an alternator is a potential problem, I'll just use marine starting batteries for the 24v bank since they are kinda half-way in between.
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