Tapping 12 volts from two 12 volt batteries wired in series for 24 volts.

[Blackstack]

I am going to run a 12 volt starter on an old mechanical diesel farm tractor I have with 24 volts. The positive on the front battery goes directly to the starter solenoid + terminal. The front battery is not grounded. The rear battery is grounded. There is a mechanical solenoid between the two batteries that when engaged will send 24 volts to the starter. My question is can I run 12 volts to the solenoid with a momentary switch to engage the gears and at the same time connect the front battery positive to the starter through the same solenoid? Well I guess I already know the answer to that is yes. But what happens when the mechanical solenoid is then activated? To start the tractor I would be holding in the momentary switch and then activating the mechanical solenoid. After the tractor is started the front battery would be grounded and the batteries would be wired in parallel through a DPDT switch or two solenoids that are activated. There would be a run and a start circuit. The tractor has just a 12 volt charging system and lights. Is there a better way to do this? Any other ideas/questions?

 

[Rand]

Sounds like a hackjob? not throwing rocks. just trying to understand how you arrived at this point
with a 24volt tractor that has 12volts all over it.

 

[jhellwig]

Why?

 

[Blackstack]

Sounds like a hackjob? not throwing rocks. just trying to understand how you arrived at this point
with a 24volt tractor that has 12volts all over it.

Mechanical Diesel should give you some idea of the timeframe of this tractor. Are you aware that early cars and most tractors into the 50's had mechanical solenoids from the factory? So what is the hackjob? I'm rewiring the whole tractor. I am using a different starter with an external conventional solenoid.

"just trying to understand how you arrived at this point
with a 24volt tractor that has 12volts all over it."

I'm just trying to understand what this even means?

 

[eljefino]

So you think your 12 volt starter motor will handle 24 volts but its solenoid won't.

An external solenoid will require a "bendix" style starter that flings its own gear in.

You can remove the very short braided output wire from the traditional on-starter solenoid that goes into the motor part, but be careful insulating it and connecting it to 24 volts in.

I suspect you'll get nearly the cranking speed using two twelve volt batteries in parallel and getting double the amps.

 

[danez_yoda]

Very confusing how you wrote it.

1) you have a 12V starter in a tractor that was designed to take a 24 V starter? Does the 12V started have its chassis grounded to the - terminal?

2) I'm guessing the thing that looks like backwards F is the mechanical solenoid? When you press it, the + of the grounded battery is connected to the - of the top battery to make the top battery + terminal 24V above ground.

3) if this is true you don't need a second button.

Connect the started - to the bottom battery + terminal (as shown). The top battery + terminal is already connected to the solenoid + terminal. When the "F" button is not pressed and keeping the two batteries separated, the solenoid - and + terminal will float at 12V relative to chassis but no current will flow. When the "F" button is pressed, the + terminal on the bottom battery is connected to the - terminal on the top battery and complete the current loop through the starter and top battery.


No the extra thing you want is for the two batteries to be in parallel when the "F" button is not engaged. That will take more work.

Question is do you need 24V for anything else besides the original starter? If not just put the two batteries in parallel and connect the starter to the terminal on the F switch that connects the two batteries together? Batteries will always be in parallel for easier charging and deliver plenty of current to the starter.

 

[Blackstack]

Why?

Why not?

I need to get the fastest cranking speed I can get. The engine is a 2-71 Detroit Diesel. Using 12 volts and a mechanical Bendix Drive after 5-10 seconds when the engine first starts to fire it kicks the Bendix drive out of engagement and you have to start all over. Using a positive starter engagement drive will solve that but I still want more RPM so want to go 24 volt. I want to keep the lighting and charging system 12 volt for obvious reasons $$$.

 

[Blackstack]

So you think your 12 volt starter motor will handle 24 volts but its solenoid won't.

An external solenoid will require a "bendix" style starter that flings its own gear in.

You can remove the very short braided output wire from the traditional on-starter solenoid that goes into the motor part, but be careful insulating it and connecting it to 24 volts in.

I suspect you'll get nearly the cranking speed using two twelve volt batteries in parallel and getting double the

"So you think your 12 volt starter motor will handle 24 volts but its solenoid won't. "

I don't know. I know the starter will take 24 volts. There are thousands of 6 volt starters being cranked by 12 volt systems for decades.

"An external solenoid will require a "bendix" style starter that flings its own gear in."

See my other post.

 

[Blackstack]

Very confusing how you wrote it.

1) you have a 12V starter in a tractor that was designed to take a 24 V starter? Does the 12V started have its chassis grounded to the - terminal?

2) I'm guessing the thing that looks like backwards F is the mechanical solenoid? When you press it, the + of the grounded battery is connected to the - of the top battery to make the top battery + terminal 24V above ground.

3) if this is true you don't need a second button.

Connect the started - to the bottom battery + terminal (as shown). The top battery + terminal is already connected to the solenoid + terminal. When the "F" button is not pressed and keeping the two batteries separated, the solenoid - and + terminal will float at 12V relative to chassis but no current will flow. When the "F" button is pressed, the + terminal on the bottom battery is connected to the - terminal on the top battery and complete the current loop through the starter and top battery.


No the extra thing you want is for the two batteries to be in parallel when the "F" button is not engaged. That will take more work.

Question is do you need 24V for anything else besides the original starter? If not just put the two batteries in parallel and connect the starter to the terminal on the F switch that connects the two batteries together? Batteries will always be in parallel for easier charging and deliver plenty of current to the starter.

I have a 12 volt starter and the starter is grounded to the bellhousing for a chassis ground. Yes, that's the mechanical solenoid. I don't know what you mean by "above ground"?

So does the small wire to the solenoid still only see 12 volts when the "F" mechanical solenoid is activated sending 24 volts to the starter? You keep spelling "started" and I don't know if you mean starter?

 

[jhellwig]

I am with you now.

I know those 1 and 2 cylinder 71 series were a little different than the bigger ones but they do make 12 volt solenoid shift starters for the 3 cylinder and up.

One way some tractors used 24 volt for starting was to connect the jumper between the 2 batteries to the frame so you could use 12 volt lights and stuff. You would have to have a starter with two terminals though.

What tractor do you have that has a 2-71? I can't think of one other that John Deere that use a 2 cylinder detroit and I think that was a 53 series.

 

[jhellwig]

Just set up your one battery that you connect the negative to the frame on to run everything other than the starter then make a jumper from the positive to the negative of the second battery then go to your starter. The only issue is charging the second battery unless you can find an alternator that doesn't connect to the frame internally. I think that is what the cucv's did.

Edit: I see what you are wanting to do after I read it again. I think there was some equipment that did exactly what you are talking about with the parallel to charge but series for starting. I can't remember what it was though.

 

[Blackstack]

 

[Blackstack]

I am with you now.

I know those 1 and 2 cylinder 71 series were a little different than the bigger ones but they do make 12 volt solenoid shift starters for the 3 cylinder and up.

One way some tractors used 24 volt for starting was to connect the jumper between the 2 batteries to the frame so you could use 12 volt lights and stuff. You would have to have a starter with two terminals though.

What tractor do you have that has a 2-71? I can't think of one other that John Deere that use a 2 cylinder detroit and I think that was a 53 series.

It's in a Super M Farmall. Detroit Diesel (before they were Detroit Diesel) had a kit to do this conversion back in the 50's but I did my own.

It uses the Farmall flywheel so my gear ratio is what keeps me from being able to spin it fast enough to start it when it's colder out.

 

[jhellwig]

It's in a Super M Farmall. Detroit Diesel (before they were Detroit Diesel) had a kit to do this conversion back in the 50's but I did my own.

It uses the Farmall flywheel so my gear ratio is what keeps me from being able to spin it fast enough to start it when it's colder out.

Are you still using the detroit flywheel in addition to the farmal one?

Starters for Detroit Diesel 2-71 Engines

We distribute new heavy duty starter motors for Detroit Diesel 2-71 engines at distributor price. We ship worldwide parts for Detroit 2-71 engines. All orders are shipped within 24hrs of confirmation.

dieselpro.com

Here is a 12 volt solenoid shift starter for a 2-71. Don't know if that helps.

New Imi Performance Ccw Starter Motor International Tractor Farmall H Hv M Mta

IMI302-005, IMI-302-005*1, Starter, 10461696, 63608D, 1107427, 1107448, 104219A2, 997870R91

www.rareelectrical.com

Here is a solenoid shift starter for an M if that helps.

 

[Blackstack]

Are you still using the detroit flywheel in addition to the farmal one?

Starters for Detroit Diesel 2-71 Engines

We distribute new heavy duty starter motors for Detroit Diesel 2-71 engines at distributor price. We ship worldwide parts for Detroit 2-71 engines. All orders are shipped within 24hrs of confirmation.

dieselpro.com

Here is a 12 volt solenoid shift starter for a 2-71. Don't know if that helps.

New Imi Performance Ccw Starter Motor International Tractor Farmall H Hv M Mta

IMI302-005, IMI-302-005*1, Starter, 10461696, 63608D, 1107427, 1107448, 104219A2, 997870R91

www.rareelectrical.com

Here is a solenoid shift starter for an M if that helps.

I am using the Farmall flywheel which is quite a bit larger in diameter that the one that came off the 2-71 motor. That's part of why I can't spin it as fast as I'd like to. That's why I want to throw 24 volts at it.

I already have the starter shown up above installed so I've already eliminated the bendix style starter.

 

[Cruzer4326]

I am going to run a 12 volt starter on an old mechanical diesel farm tractor I have with 24 volts. The positive on the front battery goes directly to the starter solenoid + terminal. The front battery is not grounded. The rear battery is grounded. There is a mechanical solenoid between the two batteries that when engaged will send 24 volts to the starter. My question is can I run 12 volts to the solenoid with a momentary switch to engage the gears and at the same time connect the front battery positive to the starter through the same solenoid? Well I guess I already know the answer to that is yes. But what happens when the mechanical solenoid is then activated? To start the tractor I would be holding in the momentary switch and then activating the mechanical solenoid. After the tractor is started the front battery would be grounded and the batteries would be wired in parallel through a DPDT switch or two solenoids that are activated. There would be a run and a start circuit. The tractor has just a 12 volt charging system and lights. Is there a better way to do this? Any other ideas/questions?
View attachment 116993

May I ask what is the make/model of the machine?

 

[Cruzer4326]

At a glance, it looks like what you're asking for is called a series/parallel switch. But, what is the problem that you're trying to solve?

 

[Cruzer4326]

Mechanical Diesel should give you some idea of the timeframe of this tractor. Are you aware that early cars and most tractors into the 50's had mechanical solenoids from the factory? So what is the hackjob? I'm rewiring the whole tractor. I am using a different starter with an external conventional solenoid.

"just trying to understand how you arrived at this point
with a 24volt tractor that has 12volts all over it."

I'm just trying to understand what this even means?

View attachment 117005


View attachment 117004

In The photo of the starter above, the starter is a Delco, early version model they identified as a 30MT. (100 series, I think...)
If you were to use a Delco 35MT series starter you could keep everything 12 volt and not modify any of the mechanicals of the engine.
It is slightly longer (about 2-3").
This is what JD did when the re-designed the 24v diesels to 12v in the early '70's.

 

[Cruzer4326]

Just set up your one battery that you connect the negative to the frame on to run everything other than the starter then make a jumper from the positive to the negative of the second battery then go to your starter. The only issue is charging the second battery unless you can find an alternator that doesn't connect to the frame internally. I think that is what the cucv's did.

Edit: I see what you are wanting to do after I read it again. I think there was some equipment that did exactly what you are talking about with the parallel to charge but series for starting. I can't remember what it was though.

It's called a series/parallel switch.

 

[ragtoplvr]

I can not speak to your specific combo., but in the old 6 v to 12 days the starter hit so hard the drive was damaged and sometimes the starter got damaged.