View Full Version : Help with 12V transfer pump.

Bob Quale
10-17-2003, 07:52 PM
I have a 12V Diesel transfer pump. I have been using It to transfer vegtable oil, and after about 3 gallons, It blows the fuse. The oil is too heavy. I have since hard wired the fuse and keep watching the pump to make sure it doesn't get too hot. I can pump about 30 gals before I have to shut down. Is there a way I can modify the pump to pump slower and not over heat? Or something like that?


10-17-2003, 08:45 PM
You could put a high wattage resistor in series, maybe a few ohms. That would limit the current. Whatcha doing, servicing elevators?

10-17-2003, 10:34 PM
We cut down the impeller on a 480 volt pump to pumped a higher viscosity chemical than designed.

What should you do? restrict the input, cavitate it slightly it should reduce the current, put a current meter in series with it and play till you get it right.. If it is a gear type pump, that might not work. Not sure.. it might still overload with restriction in the input.


Bob Quale
10-17-2003, 10:51 PM
The pump is a Diesel transer pump from Northern Tool, It's a rotory pump, little rotor with blades that ride in opening. I was thinking of maybe extending the cables to build a little resistance? I do need them longer. The thing draws about 30A so a resistor would have to be BIG, if I could even find one.

What I'm doing is this. I have a diesel truck, and I'm running it on waist vegetable oil. Now that it's getting colder the wvo is thicker and doesn't pump too well.


10-17-2003, 11:39 PM
Bob, no experience with this, but why not create a mixture of diesel and the vegge oil, maybe that would keep the viscosity within useable (and pumpable) range.

Bob Quale
10-17-2003, 11:46 PM

I forgot to mension, I'm pumping it out of the oil dumpster.


10-18-2003, 01:18 AM
Try using various lengths of 1/4" steel bar stock as a resistor.

10-18-2003, 04:33 AM
Or a strip of stainless sheet, about 020, 1/2 inch wide, maybe a foot or two length.
Another approach is to use a timer, run it for say, five minutes, let it cool five.

[This message has been edited by darryl (edited 10-18-2003).]

10-18-2003, 04:33 AM
Try making a resistor using about twenty feet of #18 wire spliced in between two pieces of # 12. Insulate the splices with shrink tubing.

Put the "resistor" in the dumpster of oil, which will serve as a heat sink. Be sure to have all of the smaller wire and the splices covered with oil. This will heat the oil a little, as well as slow down the motor.

I use a similar arrangement on my RC sailplane winches. I'm using automobile starter motors which draw a LOT of current. When I spool up the line at the end of a flying session, I need to slow the motor way down. I made a water-cooled resistor using twenty feet of #16 between two pieces of #10, in a 20 ounce bottle of water. This works well for the run time of about one minute.

10-18-2003, 05:41 AM
Using a resistor in line with power will actually hurt the motor in the long run.

Cutting down the impeller is the way I would go, or a variable bypass between the discharge and input.

These pumps were not very good as I remember, so you have to deal with that as a factor too.

WE used 3 of them pumping some light oil in one night.. Perhaps a older piston type air pump for transfer? I am looking around my storage..

Bob Quale
10-18-2003, 10:44 AM
The rotor has three blades on it, I wounder if pulling one blade out will do it? or would it off set the balance and vibrate it to death?

I'm sure I will wind up killig this pump, any ideas on what to get next time? It has to be 12V and hopefully not too expensive.


10-18-2003, 11:09 AM

My diesel has air brakes, I put a valve and quick connect on it to air up the tires. You come off the accumulator tank.. You know where I am supposed to bleed the moisture off the tank..

My neighbor uses a impact wrench with his, I am not that sure the smallish compressor can pump enough on mine.

I idled the diesel for 3 hours trying to burn up the old diesel. It is I KNOW 2 years old, motor does not have the power it used to and smokes black. I think the fuel has gelled. Diesels don't use hardly any fuel idling I found out. Under load they use very little too..

Any clue on how to boost the fuel back up instead of drain it? I hate to siphon it all out. Someone suggested I add a gallon of kerosene?

I was just trying to give you a second ideal with the pneumatic pump.

I would not remove one blade, possible machine the plastic impeller on shaft with a file a lil.. trial and error, with no return to what you had. stainless pump clearances are measured in thousandth's

Two one ways, a old cylinder and you got a pump. You'd need to fix solonoids-limit switches and a relay for the automatic operation thou. About a half gallon a stroke would be cool.. I got plenty of solonoids laying around, but they are smallish. I had one of the rotary hand pumps like went in a 55 gallon drum, it'd do a gallon or more per rotation. (gear driven)

[This message has been edited by ibewgypsie (edited 10-18-2003).]

Bob Quale
10-18-2003, 11:29 AM
I found a gear pump someone on another fourm recomended so I ordered it. 30 min duty cycle and 3 gals per min, hope I have better luck with this one.

About the diesel, kero will do the trick, you can also add some nappa diesel conditioner to stop any possible coking of the injectors. In the cold weather I use straight kero so things will start. Kero has no lubricant so you don't want to use it all the time or your injuctor pump will wear early. Nappa diesel conditioner also has the lubricant in it so I use them together to ward off trouble. Also, no road tax on kero so you can't use it over the road.


Paul Alciatore
10-18-2003, 02:49 PM
I love the idea of using a wire resistor and putting it in the oil to heat it. Kind of an overall approach. Waste not, want not. I wonder if a commercial heating element could not be found that would work. Some trial and error I guess but it might be easier to mount in the oil tank.

A disadvantage of reducing the speed of a DC motor with a series resistor is the voltage and hence the current is reduced. This causes a large drop in torque. Another approach would be to use a chopping type variable DC speed control. This sends full voltage and current on a chopped basis and therefore provides maximum torque. The motor will heat up less due to the no current phase of the chopped waveform. The variable control should allow you to find the best operating point. Unfortunately, this kind of control does not produce the heat that a resistor would so it can't be used to heat the oil.

10-18-2003, 11:02 PM
A pass transistor could work equally well for a chopper type system. Current control..

I love pass transistors, you can stack as many as it take to carry the load.


10-18-2003, 11:58 PM
I am assuming that the pump is a vane pump, in which case it is a "positive displacement" pump and not a centrifugal.

If so, messing with the vanes will not help much, it will just really reduce the efficiency. So would plumbing in a bypass and cracking it open enough to unload the pump a bit as it "short circuits". That'll also heat the oil a little.

Many of those pumps are direct-coupled, the pump is on the motor shaft. it then runs at motor speed.

Heavy oil needs more power to pump per gallon. But it slows the motor, which reduces the total power the little motor can put out, it is meant to go faster.

You really need to gear it down in that case.

If it were centrifugal, turning down the impeller could help a bit.