12 volt automotive circuit regulator

[LVZO6]

I have a 2-12 volt motor circuit with a max amperage load of 24 amps. The cars charging system can fluctuate between 12.2 and 14.7 volts. This causes the speed of the motors to fluctuate too much. The problem I am having is I would like to limit the voltage on the power supply line to these motors to a steady 11 volts. If I could even just limit it to steady 12 volts it would be ok.
Thanks for your input in advance.

 

[sophiecentaur]

If you want the supply volts not to vary then you will need a further voltage regulator to feed your motors through, in addition to the charging regulator. If you try to keep the alternator volts constant, the battery will not charge optimally.

 

[LVZO6]

I guess my thread wasn't clear. I'm asking for help/suggestions on how to accomplish this. I am not real knowledgeable on electronics but I have done a little research and I can only find ways to do this at a 5 amp or less load.

 

[sophiecentaur]

It seems that you need to buy a purpose built regulator. They are available in many different voltage and current ratings. For automotive applications, the requirement is a bit special in that you don't want to lose more than a fraction of a volt when the battery is at its minimum charging voltage and the current is high -ish but not escessive.

What is the motor to be used for? How clean does your 12V need to be? I haven't needed a more beefy regulator for any application for years so I don't know what is available but 5A seems a very modest amount for modern devices to handle. 25A has got to be easy to achieve. I was thinking that you might get some more specific information from a group more specialised in your particular project. There may well be something off the shelf and someone could, maybe, point you straight to it rather than talk in general terms. I gather that you may not be in a position to develop it for yourself, with or without helpful tips from seasoned constructors on this forum.
Could be expensive, though.

 

[LVZO6]

The circuit powers 2 fuel pumps and the items you buy of the shelf will give you a steady voltage above the target voltage I need (because that is what in normaly needed). The fuel system I built is a little more efficient than I anticipated and I need to slow the pumps down through a decrease in voltage. Could I not use 3 of these and the required heat sink and circuitry? One version of these is rated at 7.5 amps and 3 would get the job done with a variable resistor to fine tune the output. No?http://www.westfloridacomponents.com/mm5/graphics/ds5/LT1083-1085-LinearTech.pdf"

 

[sophiecentaur]

How about looking into using a pressure regulator / circulating system for the pumps? It's how it's done in most vehicles these days, I believe and you could surely get an appropriate pressure regulator for that job.

 

[LVZO6]

I have a very nice regulator on it already but the problem is how the factory system was built and it dealing with the amount of fuel I am trying to return to the tank at idle and part throttle. I had the whole system out of the car and went over every area to try and find a mechanical change I could do to get the results I need. At this point it would defiantly be easier to slow the pumps down a little than trying to reengineer the rest of a very complicated fuel system to begin with. I see many versions of regulator kits that would do what I need but I would have to stack the PCB and mount the regulator chips on a heat sink to get the current I need. They are 6 to 7 dollars each and the upgrade 7.5 amp (from 5 amp) adjustable regulators are 3 dollars each. So it looks like 60 bucks and a few hours labor and I can get what I need. I was posting on this forum to see if anybody had a "no that won't work" or "you could try this" to get the current and voltage to the target.

 

[sophiecentaur]

You clearly ahead of my thinking - always worth stating the obvious though!
As long as each pump has its own voltage regulator (two regulators in parallel could well be fighting each other) then the system should work fine.
You seem to be using a lot of fuel - what's the project?

Would it be daft just to suggest a huge return pipe to the tank? Or, if you can measure (or already know) the flow rate, you could possibly turn one pump off when the return rate gets too high (when the engine is idling). It does rather offend my sensibilities to be wasting all that electrical power in 'steaming regulators', which is what I imagine would be happening when the engine is running at normal speed.

 

[LVZO6]

Well sophiecentaur I can go into any detail level you would like in the fuel system. I just didn't want to get that "detailed" with that info on a forum that I would think has no interest in that info. You do bring up very valid points and ideas. The fuel system in on a 750+HP(haven't dynoed it yet) 04 Corvette. The factory fuel system with a single pump and an aftermarket device called a boost a pump installed (which increases voltage to 17.3V to the pump) will support max 650 HP. Even with that original system I had to do some tricky stuff in the tune to keep the air fuel ratio correct because of fuel pressure drop. A steady psi fuel pressure makes tuning easier and the engine runs smoother. So I decided to build a twin pump hanger for the left fuel tank. This is where I over did it. I should have used lower output pumps. This is where my explanation might get confusing without a diagram but I will try. The Corvette has a "return less" fuel system where the pressure is regulated in the tank and one supply line to the front of the car and that’s it. It also has 2 fuel tanks mounted in the frame behind each seat. The pump in mounted in the left tank. Off that pump you have one output line to the front, another output to the in tank regulator and one more that feeds a siphon pump in the right tank. The siphon pump in the right tank (has no mechanical moving parts) has fuel pumped through it at a certain rate which always pulls the fuel from the right tank to keep the left tank full, of course till the right tank is empty but even then the siphon pump it being supplied pressurized fuel. This is a point you could mess the system up and cause the siphon pump not to work correctly and cause yourself to run out of fuel in the left tank. The new fuel system runs one line to a regulator mounted in the engine compartment and a return line of the same size back to the left tank. This return line does not dump to the left tank though. It actually feeds the siphon pump in the right tank (through some factory lines, which are small ID and would be a huge hassle to change) and that is the source of my problem at this point. So when I did some testing I ended up with 100psi of fuel with the new twin pump system and no regulator at the front of the car, I need it to 60psi. I then removed the left side twin hanger and install a 58 psi regulator in the left tank mounted in the line that feeds the siphon pump. This still feed the siphon pump the required fuel and dumps some of the excess fuel into the left tank. I now have 68psi at the front of the car still a hair too much and with the fluctuation of the charging system it could go higher at times. This is where I would like to regulate the voltage to 11v all the time, I get the fuel flow and pressure I need with no fluctuation do to the charging system. I hope that is explained well enough and you can see why I'm going for the voltage regulation fix. If you would like pictures I can post those also.

 

[sophiecentaur]

Thanks for that info - I think I get the picture now.
It struck me that you already have some fairly sophisticated pressure regulation in your fuel supply and that a simple relay control could introduce a couple of resistors, progressively, into the supplies to the two pumps. Both would be operating at once but the voltages to the two pumps could have three states - both low, one low-one high, two high. That would keep your supply pressure within reasonable limits and the regulator could smooth out the variations as the pumps change state.
A couple of relays to switch in and out some fat resistors would be cheap enough and the control would be easy to achieve with a couple of op amps and drivers.

 

[LVZO6]

Now were talkin! I really don't need any progressive change in voltage though do to the fact I put to large of pump into begin with. If I could keep them at 11v all the time even at high boost/RPM conditions they would supply enough fuel. The fuel regulator is boost referenced so when the boost goes up so does the fuel pressure at a 1 to 1 ratio. 10 lbs of boost adds 10 lbs of fuel pressure to the base fuel pressure setting. These pumps can handle that at 11v without even working hard. I hate to keep going back to the electronic voltage regulators (cause it seems you don't think they will work) but with one of those and the correct transistor could I run the current needed. The schematic below does not have the correct values but I guess the way it's built could handle the current. ?

http://members.cox.net/jmfnd/Image15.jpg

 

[sophiecentaur]

That regulator will work fine as long as you can get hold of the right transistor and heat sink it. It will need to be dissipating nearly 100W at times (15V-11V) at 24A. It seems to me that is very much over the top for such a simple requirement.