Discussion in 'The Projects Forum' started by Projectxaccord, Mar 5, 2008.

Mar 5, 2008
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Hello, i am new here and i am in need of some help. I am trying to figure out how to limit DC voltage to a electric pump that has a maximum voltage rating of 12vdc @ 7.5A.

I am trying to install this pump in a custom project on my car, but the output voltage of my cars alternator is 14.4V@ 90A. i already have had one of these pumps installed running at 14.4 volts and after about 30 mins of running time it melted.

Electric pump specs:

Input: 6V-12V
Output: 15L/m
Current: 3.5A@6V Minimum
7.2A@12V Maximum

car electrical specs:

14.4V @ 90 amps

The manufacturer suggested that i run the pump at 9 VDC. I am looking for the easiest way to limit the voltage to the pump without building a complicated circuit or expensive circuit. I am trying to keep the cost very low as that is the nature off all DIY projects.

thanks

2. mik3 Senior Member

Feb 4, 2008
4,846
63
you can use a voltage regulator 7809

its outputs a fixed regulated voltage at 9 volts but it can supply maximum 1 ampere. You can boost its output capability by using a power transistor.

or if you can find this regulator (LT1038) in the market it would be very nice check the website

you can vary its output voltage and it can supply 10 amps

Also search for LM196 or LM396

3. John Luciani Active Member

Apr 3, 2007
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I would use the LM317. The National Semiconductor website will have schematics
for increasing the output current (and adjusting the voltage).

(* jcl *)

4. arthur92710 Active Member

Jun 25, 2007
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*EDIT*Also you could use a few 78xx in parallel. *EDIT* That wont work sorry.

The LM338 has 5-7A

Mar 5, 2008
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thanks guys,

Only problem with that is i am not very skilled in circuits like that. I googled it earlier, but it looks kinda like a complex circuit and the PDF data sheets on them dont show how to adjust the out put voltages when using the LM-??? chips in a circuit.

i was looking for something a little simpler. those types of circuits require about 3 LM-??? chips in a series type confriguration and the cost for each chip is about 12-15\$. if i were to construct a circuit using those chips the cost of the circuit would be more the the cost of the electric pump itself.

I got stuck with this pump due to the distributor of it stating false information on the pump. So i have to try to make something work but trying to be VERY cost effective also.

thanks

6. thingmaker3 Retired Moderator

May 16, 2005
5,072
6
I don't know where you are shopping for parts, but don't go back there.

http://www.goldmine-elec-products.com/prodinfo.asp?number=A10662

7. S_lannan Active Member

Jun 20, 2007
247
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a cheap and dirty way to solve this problem is to put a few big diodes before the motor. eg 4 diodes would drop 2.8ish volts. leaving 11.6v to feed the motor.

cheap and dirty.

old trucks used to use a big diode pack to drop 24v to 12v in order to run 12v car appliances.

8. SgtWookie Expert

Jul 17, 2007
22,183
1,728
Attached is a schematic for a simple and inexpensive 9.2V 10A regulator.
5 components:
1) TIP141 NPN Darlington 10A transistor
2) 1N758 10V Zener diode
3) 1k Ohm 1/4 Watt resistor
4) 330uF electrolytic capacitor

One vital component not shown in the schematic is a heat sink. You will need one. A good source for a "freebie" would be an old CPU heat sink. Take the fan off, drill a hole and use a self-tapping or sheet metal screw to mount the TIP141.

If you want the voltage lowered, you will need to replace the 1N758 with a lower voltage Zener. A 1N757 is 9.1V, which will give you about 8.4V output.

There is no protection for overcurrent. Should the output become shorted, the TIP141 will self-destruct unless you protect it with a 10A fuse.

Electronics Goldmine is carrying TIP146 Darlingtons you can use instead of the TIP141. They're selling three for a buck.
[eta] Oops - no, you can't use the TIP146 as they are PNP. You need NPN in this circuit. TIP142 will work fine, they're a buck each:
http://www.goldmine-elec-products.com/prodinfo.asp?number=A10573 (URL changed to point to the TIP142 instead)
E.G. doesn't have the 1N757 or 1N758, but they DO have a bundle of 15 1N755A's for a buck:
http://www.goldmine-elec-products.com/prodinfo.asp?number=A10075
You could use the 1N755 in series with some standard rectifier diodes like 1N4001's etc to increase the voltage. Four 1N4001's in series will drop roughly 2.5V. That in series with a 1N755A will give you about 10V at the base of the TIP141, which will give you about 9.2V out.

Zener diodes are used in reverse bias; eg: cathode (the end with the ring, or where the triangle is pointing) towards the positive supply.
If you used additional standard diodes in series to increase the voltage of the Zener, the cathode goes towards ground.

• 9.2VRegulator.PNG
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Mar 5, 2008
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wow this is great! what voltage will this circuit yeild if i use the TIP146 instead of the TIP141? Or is it the same? I also have 1 more question, what is the component at the begining of the circuit labled as V1 it is a square with a squggle in the middlle of it and has 1 kHz by it.

When using the 1N4001 in series do they go before the zener diode or after?

10. SgtWookie Expert

Jul 17, 2007
22,183
1,728
Please re-read that section of my post; I later corrected it after I suddenly realized that the TIP146 is a PNP-type Darlington, and it would not work in this circuit; instead you would wind up with about 13V out and a fried Zener diode.
I changed the link to point to a TIP142, which is NPN and it WILL work; unfortunately they are \$1/each instead of three for a buck. Basically, in the TIP1nn series, the ones that end in 5,6,7 are PNPs, and the ones that end in 0,1,2 are NPNs. TIP14n's are all rated for 10A continuous current. The basic difference between them is the maximum emitter-collector voltage rating, which you don't have to worry about in your application.

The thing at the beginning labeled V1 is a "signal generator" used in Spice simulations. I have it set to simulate a sine wave that varies between 11.6V and 14.4V, which is a reasonable voltage range to expect from your electrical system (battery + alternator).

On the right, M1 represents your fuel pump motor.

They CAN go either on top (next to the TIP141's base) or underneath (near ground) - however, you may wish to put four of them in series on the ground side; that way you can either short a portion of that series circuit to ground to lower the voltage, or jumper across a diode (or two or three) - it just gives you more options.

The voltage out of the emitter of the TIP141/142 will be about 0.8V less than the voltage on the base.
So, with just a 1N755A Zener diode in reverse-bias with the 1k resistor, you would have 7.5V at the base of the TIP141/142, resulting in about 6.7V output.
An 1N400n (where N=1 to 7) rectifier diode drops roughly 0.63 volts across itself when it is forward biased (conducting) at low current levels. So, for every forward-biased (band nearest the ground) 1N400n diode you add to the ground path of the 1N755A Zener, you boost the voltage on the base of the TIP141/142 by 0.63V, and as a result, the output of the emitter increases by 0.63V as well.

Some more notes:
The TIP142 has it's collector both on a pin, and connected to the the tab used to fasten it to a heat sink. This means that battery power will be connected to the heat sink, so you must make sure that the heat sink doesn't touch ground anywhere unless you like bright sparks, blown fuses and walking.

The electrolytic capacitor: "rule of thumb" for electrolytic capacitors is to select one with a working voltage that is twice what you expect to see in the circuit. Since your alternator puts out 14.4v, you're looking for a working voltage of 28.8 or more. It doesn't matter if it's a LOT higher, just so long as it's higher. If you were desperate, you could use one rated 25v. Going lower than that is begging for disaster. When electrolytic caps fail due to overvoltage, they go out with a loud "Bang".

Also, 330uF is not a "hard and fast" number. You could use a fairly wide range; about anything from 100uF to 470uF would work fine. If you wanted to use something larger, you would have to increase the wattage of the 1k resistor, as it will see a large spike in current when the cap is first charging.

Mar 5, 2008
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I just made a sketch of the schematics. does this look about right? using the components listed above. the 1n4001 in series with the Zener 1n755a diodes. Please correct me if i am wrong.

Mar 5, 2008
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thanks you very much for the explaination Sgt. Wookie! If that schematics i made up is correct i will construct this circuit and post up the results.

13. SgtWookie Expert

Jul 17, 2007
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The transistor is a TIP142 (you left off the "I") - otherwise, you have it

You should download a datasheet for the TIP14x series before you attempt to connect it up.

I think there was a link to it on the E.G. website. If not, I suggest you go to the Manufacturer's website; or failing that, try a datasheet search side such as:
http://www.alldatasheet.com
Use the "starts with" option, and for the search string use "TIP14" (without quotes)
Note that Motorola's semiconductor divison has been detached and renamed; some components are now made by "ON Semiconductor" and some by "Freescale", exactly which makes what I have no clue.

I'm not familiar with the fuel system on Accords, but be aware that fuel pressure and fuel flow are related but not the same things, just as voltage and current are related but not the same!

Your challenge is going to be maintaining sufficient fuel pressure at the maximum fuel flow that your injectors require, otherwise fuel starvation will occur. This situation may not become apparent until your engine is operating under open throttle near the top of the RPM range. Fuel starvation will rapidly lead to detonation and severe engine damage (broken/burned pistons, ring lands, hammered bearings, etc.)

Excessive fuel pressure should be vented back to the tank via a pressure regulator already plumbed in the circuit, but if you're pumping far more fuel than necessary, you will be heating up your fuel, which can also result in fuel starvation due to the fuel boiling.

Make certain that your fuel pickup screen in the tank is clean, your fuel filter is not clogged, and that your fuel pressure regulator and return circuit/plumbing is working and in good condition. Electric fuel pumps will rapidly self-destruct if they do not get a constant flow of fuel; as that is how they get rid of heat generated by the motor.

14. Ron H AAC Fanatic!

Apr 14, 2005
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That is gonna take one mozam heatsink, especially if it is mounted under the hood. How come no one mentioned PWM? I thought that PWM was a good way to power a DC motor. Is this not a motor-driven pump?

15. SgtWookie Expert

Jul 17, 2007
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1,728
Yep! However, it's likely going to be passing in the neighborhood of 5A - and the heat sink deal has already been mentioned. In a car that's moving, that should help keep the temps under control.

Good point!

Well, I actually DO have a simple PWM control circuit posted in the projects collection that would likely take care of the situation, were the MOSFET upgraded. However, it seems that some folks just starting out have had problems getting things like that working with the minimal amount of test equipment they have on hand. I certainly don't like to leave people high and dry, but OTOH, I don't have all day to sit on the forum in case they hit a brick wall on a project.

This is a good (and functional) beginner's experiment that is not hard to understand or connect up, and can be very easily troubleshot with just a few voltage readings using the cheapest meter on the planet. PWM isn't quite that easy to understand for many newbies, I'm afraid.

Mar 5, 2008
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I actually modify engine management computers, i am a intermediate at soldering and troubleshooting. but circuits like these i lack schooling on it but i can follow a schematic pretty well.

as far as this voltage regulator circuit i can remount mount the board inside the car somewhere and add a small cooling fan to it.

Ron H,

What do you mean by a motor driven pump? Its a external small 15L/ min dc pump. I am using it to as a pump for a custom liquid to air intercooler setup i designed for my turbo car. I acutally purchased it and it turned out to be not what i needed. So i got stuck with this pump and had to figure out a way to make it work.

SGT. Wookie,

I am slightly familar with Pulse width modulation, i am sure if there was a schematic for it, i could probably build it with no problems. I have designed and build my own electronic boost controller using a 12vdc solenoid valve and pressure switches.

But like anyone of my stature, I like learning so trying to build that PWM circuit would be pretty fun.

Ill look into it.

Mar 5, 2008
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I just took a look that the simple pwm circuit in the projects collection forum. What is the average cost to build that pwm circuit?

18. Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
I thought we were talking about a fuel pump. I'm not sure if all fuel pumps have DC motors in them. Some may have what amounts to a solenoid - I don't know. It sounds like what you have is not a fuel pump - or are you adapting a fuel pump for use in your intercooler?
Can you post the datasheet, or a link to it?

19. SgtWookie Expert

Jul 17, 2007
22,183
1,728
CMOS circuits are plentiful and inexpensive. I can get the 4093's at a local supplier for 2/\$1. 40106 hex Schmitt-input inverters would work, too - or any other CMOS gate that has a Schmitt input and an inverting output.

The most expensive parts in that "simple PWM circuit" are the potentiometer and perhaps the power MOSFET. You could use something like an IRFZ24, IRF520, IRF640, etc.

You would also need a cap and diode across the motor, or the reverse EMF spike will zap the MOSFET. The cap could be a 470pF to 2200pF ceramic. It's purpose is to absorb the reverse EMF spike until the diode has time to conduct. The diode's cathode goes towards the power supply.

You would probably want to use a higher frequency than 1kHz, as the pump motor would tend to "telegraph" the 1kHz tone through the fuel lines, and you'd hear it. However, since this circuit will be used to drive a moderate power load, it would perhaps be a better idea to use a 555 timer, as the output can source/sink 200mA compared to a 4093B @ 10mA; the MOSFET would spend less time in the linear region thus generating less heat.

Unfortunately, I have to get going at the moment - busy morning ahead.

Mar 5, 2008
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No is not a fuel pump, a fuel pump wont last that long when using it to pump water, If i were to use a fuel pump i would have to buy high pressure lines and fittings. Also I would have to add something to the water that will lubricate the inside of the pump . All i required was a pump that could accept 1/2 low pressure lines and flow enough water to transfer it through the system.

here is a link to the exact same pump, i couldnt return it because i purchased it on ebay.

http://cgi.ebay.com/15L-Mini-DC-Wat...ryZ46547QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

This was the only pump that i could find that matched the inputs and outputs that i needed. Similar ones were in the \$100-250.00 range and thats just to expensive for a pump that only runs when you are at 80% throttle position, and just for a few minutes at a time.

The way that i have it all set up is, the trigger for the pump is wired to a Throttle switch, then there is a master override switch to be able to turn the pump on at anytime regardless of throttle position. Eventually i am going to install a thermostatic switch in place of the throttle switch so that the pump will turn on when the air intake temps are above 90 degrees F.