I need a little DC voltage help......

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Nov 12, 2010
I need a continuous stirring motor on my home made pesticide spray tank.... It will be stirring the chemicals for several hours at a time.....

I am thinking of using a DC drill motor... the batteries are dead and won't charge..... I have a 9.8 DCV Dewalt and a 18 DCV Bosch ...... I have 12 DCV supply...... both motors have 2 speed chucks for low or high speed operation.... I'm stirring a 15 gallon tank and I'm using a paint stirring paddle....

the ends of the blades have been trimmed down to about 2 1/4" diameter so it will fit through the bung.... I'm thinking of installing a bracket to clamp the drill motor to the tank.... using the chuck to hold the stir paddle....

Which motor should I use..... will the 12 V supply be "harder" on the 9V or 18V motor... do I need to add an electrical device in the DCV supply....

Both drills have variable triggers but my intent was to use the 2 speed chuck and clamp the trigger down tight.... one of the 2 speeds should get me a decent mixing speed......

From everything I have read.... some say 12V will overheat the 9V motor and others say 12V will overheat the 18V motor...

Which motor would you use and teach me something about DC motors...

OR what should I do to make this stirrer right..... "BOT MOTOR" maybe....
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Let me think about this. 

My first concern is the drill motor running for 30 minutes at a pop.  I don't know what the duty cycle of those is as when used as a drill, it generally is used in short periods of time with resting between screws.  You may have an overheating problem no matter what voltage you run them at.

Second concern is cutting paddle blades down means you need to increase the rpm's to keep the circulation up as you are moving less surface area.

I'm thinking if you take a rod and put a slit in the end, you can then insert a flexible rubber like flat paddle that will fold/curl to fit through the bung and then open up inside.  Since we are talking about chemicals being mixed, you need to make sure the rod and paddle material is non-reactive with what you are mixing.  If metal is out, try delrin rods.  You don't need real high rpm's as that could cause cavitation and foaming.  You want just enough surface area to stir the mixture at lower rpm's

You can buy 12v high torque and low rpm motors for under $20 that might be better suited for this project than a drill conversion.  Something like this 25rpm model.


Perhaps the simplest option is a 12v BBQ grill rotisserie motor.  There are a lot of them that run on D batteries or have a 120v ac to 12v dc step down circuit inside the housing.  Just find one that runs on D batteries and you are good to go and only have to mount the stirring rod to it.  With a thick delrin rod, just drill one end so the shaft of the motor fits inside. Then cross drill and pin the rod through the shaft to lock them together.  Use a small cotter pin and you can disassemble it as needed.  Plus the grill motor will already have a mounting bracket with screw holes on it making it easy to mount.

If you want to "frank-en-mod" it, you could.....

Buy replacement batteries and then McGyver the drill by taking out the trigger and rigging a DC timing circuit that will run on the drill battery voltage.  Have it "stir" the mixture for 10 seconds every 30 or 45 seconds and it might do the job without worries of overheating the drill.  It would also be possible to simulate the variable speed feature by using an appropriate value resistor in line to mimic the voltage through a partially pulled trigger.  If you really want the full McGyver, use a tie wrap to partially "squeeze" the trigger to the desired rpm range and then use the timer circuit to open and break one side of the wiring to the switch.  Hell, duct tape the timer to the side of the drill and you are about as McGyvered as it can be
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Dave and Stan..... good ideas.....

well, the drill motor is out........ I like the gear motor....... The high volume pump is a good idea also....

I think 2,4 D eats some plastics and rubbers.... I know it eats a garden hose when I repeatedly spray over it when it's laying on the ground....

I think for now, the gear motor is a front runner...

Now I have to work on a coupler.... maybe a compression to compression fitting if they will fit the shaft..... or drilling and pinning some sort of tube....... They make continuous stirrers for several hundred bucks but that ain't happening.....

Soooo, I need to test the stir speed, using the drill motor, to find the right RPM for the stirring paddle I want to use....

I'm thinking 200 - 600 RPM or something like that..... don't know for sure...... some of the chemicals have a fairly high viscosity and don't mix all that well.... then there are wettable powders that will settle out of solution, if the mix speed isn't high enough...

Wish I had a strobe light to measure the mixer blade speed....
A DC motor can run on many voltages, up or down.

A Drill motor is way over powered for what you need.

Over heating a motor is voltage as well as actually load dependent. If you don't overload, it can be on higher voltage without overheating.

The higher the voltage, the higher RPM.

A DC magnetic motor is reversible.

A DC universal motor can be rewired to be reversible.


Make yourself a magnetic stirrer. Great for mixing chemicals.

You can get two powerful rare earth magnets from an old hard drive, or buy on eBay.


2,4-Dichlorophenoxyacetic acid is some strong stuff.  What are you trying to kill, Kudzu?

At times I need to kill stuff and not kill the grass next to it... or it's added to glyphosate to do in a host of unwanted veggies.....
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A DC motor can run on many voltages, up or down.

A Drill motor is way over powered for what you need.

Over heating a motor is voltage as well as actually load dependent. If you don't overload, it can be on higher voltage without overheating.

The higher the voltage, the higher RPM.

A DC magnetic motor is reversible.

A DC universal motor can be rewired to be reversible.


So now I will try the 9.8V and do a test..... check for RPM in both chuck speeds... check temp using IR gun... maybe even check for ampere draw.... if my DC amp meter will go that low....
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You can get a 12v to 9v  3 amp step down converter on amazon for $1.58 free shipping. What is the amp draw for the drill? You can make a step down converter there are lots of DIY plans on line or just buy one. You can make or buy an adjustable converter too.

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