24V and 12V

[wallguy31]

This is going to seem like a very stupid question to most of you guys, but I recently bought a small jon boat for river fishing with a new yamaha 60 jet. I own a 24V bow mount trolling motor that I would like to use on it, but instead of wiring in two batteries separately for the trolling motor, I was wondering how I could set the auxilliary circuit (trolling motor) up for 24V using the starting battery and one other battery without compromising the main 12V circuit that goes to the fuse board, the switch and the motor? Can I do this with isolators or is there a better option?

[JPC]

Hmmm...

This is my Physics response, rather than my sailboat response, which means it's much less reliable but will hopefully prompt corrective posts from other members:

- what is the amperage requirement of your trolling motor?

- I'd go with a step-up transformer (two concentric coils) between your 12-volt system and the 24-volt motor.

JPC

[Tim B]

a step-up transformer with DC.... interesting idea. transformers change AC voltages (and even if you could, the weight might sink the boat).

The solution is to use 2 x 12 volt batteries wired in SERIES then have a seperate battery for any 12 volt services. Most DC motors can use PWM speed controllers, and there are plenty of circuits/examples on the web if speed control is an issue. Also, use an on/off switch or relay that will handle the current is a necessary safety feature.

Tim B.

[longliner45]

will the cost of conversion be less than buying a 12 trolling motor?

[wallguy31]

The problem with three batteries, 2 in series for 24V and one for 12V is that there is no space for three batteries. That's why I was wondering if it was possible to have two circuits one with 12V and one with 24V from two batteries. It seems to me that if you used battery isolators to isolate the second batteries ground it should be possible unless I don't understand how battery isolators work. I guess my understanding is they are a large scale diode or one way valve. So why can't an isolator be used to isolate the two circuits? Conversion to a 12 V trolling motor would cost less than ordering a custom gas tank to accomodate a third battery in storage.

[Tim B]

You could take a 12 volt feed off the more negative of the two cells, though that would induce a difference in voltage between the two cells which would reduce the ultimate lifetime.
Another solution would be to regulate the 24volt supply down to 12 volts using several LM2585T-12 available from Farnell electronics.

Tim B.

[JPC]

TimB-

Maybe you've corrected my error, or maybe I just communicated poorly (or both!), so I wanted to check.

What I had meant by my prior post was the form of "transformer" that uses an induced coil: two concentric coils (sometimes with a ferrite rod in the very center). The ratio of winds in one coil versus the other determines the ratio of change in voltage from the charged to the induced coil.

Amperage requirements might make this totally unfeasible (heavy wire guage), but I'm not sure.

Sounds like you know, but I'm not sure you were correcting the set-up I meant.

-JPC

[Tim B]

There must be a description of how transformers work, somewhere on the web, and I'll let you search for the full answer. In breif, a transformer converts voltage by means of a fluctuating magnetic field moving through a coil. This magnetic field is generated by a "primary" coil. Assuming the coils are still relative to each other (likely) and do not gain and lose turns (also pretty likely) and the magnetic resistance of the material in between doesn't change (it doesn't), then the CURRENT flowing through the "primary" coil must change.

Therefore, in the case of batteries, you can't use a transformer directly because the resistance of the coil is constant, the voltage is constant, and hence the current in the circuit is constant, so you'll see no power at the other end of the transformer.

If you really want to use a transformer, you would need to build an inverter (NE 555 Astable circuit) with the transformer on the end, then rectify the voltage afterwards. This might be a little expensive. It will also not give you huge amounts of power.

My preferred way (if you only want 2 batteries) would be to use the voltage regulator (or several in parallel) I mentioned above.

Tim B.

[Andina]

We are just now in testing of our Trollbridge Combiner that allows you to charge a 24 volt battery from a 12 volt alternator using either the starting or an existing house battery for the bottom end of the 24 volt supply. It is fully automatic.

Production is expected about the end of May and cost is under $100.

There is a draft of the owner's manual at http:www.yandina.com/acrobats/Trollbridge.pdf

If you want to be notified when it is available, send your email address to sales@yandina.com and we will put you on the notification list.

Any technical inquiries welcome at tech@yandina.com

[george allard]

Save yourself a lot of headaches and go to a 12 volt trolling motor.

[longliner45]

some of the guys at work say almost all trolling motors are 24volt.but they run them on 12? I asked if that would burn up the motors? they say that they have had no problems,,,been doing it for years ,the motor just runs slower.
,,,,,I will investigate this further.

[Tim B]

running a 24 volt motor on 12 volts will run it at (roughly) half speed there are no problems.

Do NOT run a 12 volt motor on 24 volts. It will burn out, and you'll look very silly (and out of pocket).

I think the easiest way is to solder up some voltage regulators and put them in a box as I suggested earlier. Your 12 volt supply then comes from the regulators (and is exactly 12 volts).

Tim B.

[george allard]

12 volt electric motors are available with up to 45 # of thrust.

[StianM]

If you want to transform DC curent you nead to do something I think is called ripeling. This is DC curent that is cut in so quicly that it apears to be normal DC.

I think this is in use in airplanes so a flight mecanic or flight electrician should know about it. The higher the Hz or ripling is the smaler transformator you can have.

I would also sugest using two batterys 24V and take out 12V ocer the poles on one off them. I'm not familiar with the disadvantages this will have on the battery

[Andina]

You are referring to DC-DC converters that can convert 12 volts to 24. And you are correct, the higher the frequency the smaller the transformer. However for a trolling motor current the cost would be prohibitive and more than the trolling motor itself.