24 volts and the 700r4

[Gunfreak25]

Anyone know how the 700r4 would work on 24 volts? I know things like switches work on either 12v or 24v and many are sold labeled as such. However the 700r4 is full of hydraulic solenoids which I am sure need to see the voltage they are wired for (12v).

I guess the proper question is how do solenoids designed for 12v work on 24v? If they function twice as vast due to the doubled voltage I could see where this would cause concerns in a transmission.

 

[SouthernSteel]

When the 700r4 came out it was based on a 12v platform why would u want to use 24 volts for that tranny the only thing that is 12 volts is the kick down the rest of the trans is mechanical

 

[Gunfreak25]

I installed a 700r4 K case into my 6.2L M211 which is 24v. I opted to stay with 24v because for the additional $90 it costs for an extra battery I get to keep all of my original gauges, IP solenoid and light bulbs. Plus I feel 24V is more advantageous over 12v, just my op.

I thought the 700r4 had some other internal solenoids aside from the lockup solenoid? In any case it's not a huge deals since I have a 720 watt 30 amp converter and the lockup hardly uses any power.

Just thought if I could avoid having to wire my tranny through a converter I would do so, for redundancy's sake. But, it's all good.

 

[jwaller]

there is only 1 solinoid in a 700R4 and it's for the TCC clutch. Its about $15 to replace and is easily done with a fluid change. Go for it and if it fails your not out much.

 

[patracy]

I would add a resistor inline for the TCC solenoid. Just need to know how much current it pulls to calculate the resistor that would lower the voltage seen by the solenoid.

 

[SouthernSteel]

Ok first thanks for not jumpin me though it was wide open gun freak i respect u for that i wasnt tryin to be a smart alec i guess i just didnt see the point my bad for what ever reasons do what ya gotta do

 

[Gunfreak25]

Thanks for the clarification. I looked it up and the solenoid only draws .5 amps. If the solenoid saw 24v it would in theory cause the torque converter to lockup twice as fast correct? I don't think this is a bad thing since i'll only be using lockup under a few conditions. 1 being anytime I see 50+mph which will be rarely. 2 i'll only use lockup under no load conditions. So from a friction standpoint a faster lockup would be beneficial to clutch life, less slippage right?

It is a cheap easy to replace part. I guess the question is will the solenoid work on 24v without frying? It hardly uses any power.

 

[Carl_in_NH]

The coil will overheat and burn out - it will just take time. How much time? Depends on how well built it is - but it will fail. Use a dropping resistor.

 

[patracy]

Ok, if the solenoid draws .5 amps, then that means it uses 6 watts.

24v - 12v = 12v / .5 = 6 ohms to reduce it.

Something like this speaker resistor should do the trick.
Amazon.com: Dayton Audio DNR-6.0 6 Ohm 10W Precision Audio Grade Resistor: Electronics

It won't regulate current as load increases, so it will see a little higher voltage than 12v when the engine is running. But then again, that solenoid is used to 13.5-14V to start with.

 

[Gunfreak25]

Nice, thanks V. So this resistor, does it reduce the voltage from 24 down to 12 or do I still leave the trans hooked up to the voltage converter I have on the firewall. Electronics were never my strong point.

 

[patracy]

Installing the resistor inline would allow it to be wired to 24V. The load would be reduced to ~12V at the solenoid.

 

[papakb]

Back to school patracy,

You were on the right track, just got the formulas swapped.


R = V / I

R = 12 / .5 so R = 24 ohms

P = I x E

P = .5 x 12 so P = 6 watts



So a 10 watt, 24 ohm resistor wired in series with the +24 volt supply will drop the voltage to 12 volts and keep the solenoid from frying.


Kurt

 

[Gunfreak25]

Thanks guys! Do you think will be more reliable than the step down converter?

 

[armytruck63]

The resistor would be much more reliable since it is only one part. Make sure you mount it in a location where air can circulate around it to prevent over heating.

 

[Carl_in_NH]

There's no need for the added complexity of the step-down converter - the resistor is the simplest solution. Simple == better, in my book.

As stated in the formula, this resistor will dissapate 6 Watts and will therefore get quite warm; mount it in an place where air can flow around it and nothing that will get damaged by the heat (like wire insulation) is touching it.

EDIT: Looks like Armytruck63 and I were typing at the same time

 

[Gunfreak25]

It's so simple. Why don't more people use these resistors? Are resistors usually used for small low power items?

 

[Carl_in_NH]

Many times, yes - when the power to be delivered to the load is fairly low and voltage regulation at the load isn't critical a resistor is the simple and robust solution. In this case both points are true. Other loads (like a radio) would warrent a different solution, like the DC-DC converter.

A DC-DC converter would be more efficent in terms of not generating 6 Watts of waste heat (more likely a few tenths of a Watt with a modern converter) compaired to the resistor, but in a vehicle application like this I tend to favor the simple solution at these power levels.