whidbey1

My Feedback: (9)

Hello
I just got a large starter for starting Giant Scale engines, the diagram that comes with the starter shows a jumper between the battery banana plugs to run 24 volts. I saw someone had a toggle switch so he could select 12 or 24 volt.

Does anyone know how to set the switch up and what type of switch to use?


Thanks in advance

Bill

Rodney

These switches need to handle very high currents so choose a switch accordingly. It should be capable of handling well in excess of 20 amperes. Just check the specifications on any switch you plan to use. If they do not publish the specifications, beware. Note that there are two switch current ratings, continuous and switching. Switching current is alway the lower one as there can be lots of sparking and pitting just as the contacts are closing on a high current demand load. One with wiping contacts is better than one with just pressure contacts as they are somewhat self cleaning as the wipe tends to get rid of any pitting and corrosion.

piper_chuck

My Feedback: (12)

The box Ihave for boats doesn't have any switches. Instead it has four banana plug jacks. With these four Ican charge either battery, get 12V from either battery, or get 24v using both batteries in series. It also has a power panel for the glow driver. I'll gry to draw up the wiring and post it...

piper_chuck

My Feedback: (12)

Here's the wiring diagram for the starters. If you include a power panel, connect it to either battery.

bob62

My Feedback: (28)

Please do, I would to view it

whidbey1

My Feedback: (9)

thank you guys

Roary m

My Feedback: (67)

I run a Dynatron with a couple of 12v gel cells wired in series. I wouldn't bother with 12v with anything over a 40.

RCVFR

My Feedback: (7)

Greater voltage gives greater speed on the starter. Greater Amps give more "grunt" (torque). Bigger engines need more grunt.

Rodney

The size of the wire (gauge) is very important. You will be surprised at the difference is between a 16 gauge wire and a 10 gauge wire between the battery and starter motor. Very often, just increasing the gauge of the wire will let you get by with 12 volts where you formerly needed 24 volts. Also, keep that wire between the battery and starter as short as you possibly can and make very good connections at all junctions; i.e. no alligator clips, lots of contact area and high pressure or solder.

piper_chuck

My Feedback: (12)

While this might be true, it's important to note that total power is a function of both current and voltage. The total power available at 12V is not as high as it is at 24V. In addition, the wiring within the motor limits the amount of current that motor can handle. Exceed the capacity of the motor windings and you'll burn it out. Increasing the voltage reduces the current requirements as well as increasing the total power.

In more practical terms, no matter how big a battery Iuse, Ican use my hand to stall my starter when it's on 12V. When I try the same with 24V, Iget a friction burn.

Roary m

My Feedback: (67)

Before I had read the above post, I had the same response. The trouble with some of the starters out there is that you can have a 900 amp battery hooked up to the 12v starter and due to the quality of some, they just will not turn over with more authority. I don't disagree with electrical theory but I have hooked up some of the knockoff brands to car batteries with heavy gauge wire and I can stop the starter by holding it. I dont know if the windings are wound to a minimum length or what. I went to the Dynatron to get the omph. Unfortunately, it's running at around 100$ now.

Jazzy

This is interesting. Consider the following:

2, 12v batteries capable of delivering 10A each.
In series you have 24V and 10A. This gives 240W of power.
In parallel you have 12V and 20A. This gives 240W of power.
Looks like the power is the same - all things being equal and the current being unlimited.

Torque however is a result of RPM coupled with HP.

I can tell you that running a motor designed to run at 12V WILL burn out faster at 24V than at 12V. It WILL spin faster at a cost - there is no such thing as a free lunch. (But I'll probably end up doing it to start my gas engine.)

The windings and field magnets are chosen to handle a certain amount of current at a narrow voltage range - simple design parameters. The windings do not limit the current. They are simply bare conductors with a varnish coating. Too much current and the wires either burn through creating an "open" or they short together. Either way = dead motor.

Too much voltage (even if the current is limited) will produce too much electromagnetic field resulting in an undue amount of heat build up. The motor cooks.

At short bursts there shouldn't be a problem with running a starter at 24V. Whatever works for you.
As mentioned above by Rodney, use the appropriate size wire and connections. It DOES make a difference.

There are a variety of starter motors for ATVs, motorcycles, riding lawn mowers, etc. that may provide the torque at the voltage you are looking for. It's been done before so I thought I'd share that little tid-bit. You might be surprised at what you find along side the road, in a junkyard, repair shop, etc. DIYs love doing this kind of stuff!

I use to use two 1500mAh, 7.2V, sub-C packs on my Tower starter. It would start up to 1.08 2-strokes and 1.20 4-strokes. Compression had a lot to do with whether or not the engine would turn over.

Best of luck and Happy New Year!
Jeff

jester_s1

The 12v and 24v comparisons so far haven't taken into account the draw down that happens in a real world application. The more load there is on the starter, the lower the voltage gets as the amp draw goes up. So with a typical 12v gel cell, you may only have 10v when starting an engine. If you're stalling the starter, you may be as low as 8 volts because you're trying to pull more amps than the battery can give you. But going to more voltage gives you more room to drop down and makes it possible to draw more amps, so in a 24v setup you might have the same amount of draw down, but in that high load scenario you'll still have 16v which is enough to shove the thing on over.

piper_chuck

My Feedback: (12)

You can't assume the current is unlimited, the windings and brushes in the motor can only handle a finite amount of current.

The torque at 12V will not be as high as the torque at 24V. For example, the Dynatron specs say it has 340 in-ounces at 12V and 680 at 24V.

And Ican tell you that several starters, Sullivan Dynatron for example, are designed for 12 OR 24 volts.

Exactly my point, try to push too much current through the motor and it'll burn out.

Jazzy

Piper et al,

I only clarified some things that were misleading to help others learn AND offer suggestions for alternate possibilities.

My initial paragraph starting with, "Consider the following:", indicates that the following material is theoretical - for thought. The end of the same paragraph clearly states, "...all things being equal..." which also implies an ideal situation.

It was only to show that the power is the same. What I should have said was that "all things being equal and voltage and current being constant" - my bad. Again, in an ideal situation. This is the theory to support my statements and to show the readers that Power=Voltage * Current.

I didn't have time to go into the voltage drop which occurs when drawing current from a finite source - thanks for clarifying that Jester. This is exactly why the two small packs I use work well. They have a nominal voltage of 14.4V (but charge to around 16.X floating voltage) so that when I begin to draw current the voltage drop is not as far below the voltage rating of the motor as it would be with only a 12V source. Note the current rating of the supply hasn't changed but more power is consumed.

Never once did I mention a starter rated for 24V yet it appears you think I did. I clearly define my statements as being related to a 12V rated starter. So when you reference my statements and apply them to 24V rated starters you are comparing apples to oranges. I am referring to this:


Unfortunately, I got caught up in the 12V aspect when Bill's starter IS rated for 24V use.

I firmly stand behind every statement I made in the context it was made. It is important for our fellow modelers to understand that exceeding a motors ratings has consequences.

If you feel I slammed you then I am sorry - that was not my intent. We should all get along and help each other.

Best Regards,
Jeff

Jazzy

Whidbey1 (Bill),

I noticed that you asked for a switch diagram for 12 or 24V capability.
The following is a diagram for wiring up two 12V batteries to get either 12 or 24V. It is simple and sound.
The switch shown is Double Pole-Double Throw (DPDT) and is usually available at most auto parts stores for under ten bucks.
I would recommend a three position switch (ON/OFF/ON) so that there is no voltage at the terminals in the center position.
There is a jumper between two of the terminals (shown in blue if you can see it).
Choose a switch that has a current rating of 20A or more and use 12 AWG wire at a minimum.
You can use "banana jacks" as shown or whatever you choose.
Depending on the switch you choose you can either use crimp-on ring terminals or female Sta-Kons to attach to the switch terminals.
Use caution and wire the switch before connecting the wires to the batteries. Double check your connections and put heat-shrink over the exposed connections to help prevent accidental shorting or worse.

Let me know if there are any questions.

OliverJacob

My Feedback: (12)

I am looking for a starter capable to turn a 50 cc gas engine.
This should be running on 12 Volts, I use a 50 Ah car battery which provides plenty of current.
Since I am not sure if the Dynatron has enough torque, I thought about getting a motorcycle or lawn mower starter.
Has anybody tried this yet?