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Help rigging up a 12/24 relay to boost voltage.

4K views 29 replies 7 participants last post by  toddalin 
#1 ·
Similar to the old school 12/24v starter setups I’d like to wire my fuel pump to have the ability to briefly zap it with 24 volts to get more out of it. How would you suggest doing something like this?

I was thinking of running a $17 mini motorcycle 12v batteries right next to my current battery. Tied into the system in parallel so it charges normally. Then need a way to apply voltage in series to the fuel pump only while isolating the rest of the system. What route would you take on something like this? How would you wire it?

I’m assuming some sort of DPDT relay? Just not sure what the best way to wire it up would be.

Doesn’t look like the pumps draw a ton of amps. I had planned on 60 base pressure and no more than 20lbs of boost. So 80psi max pressure. I’ve spoken with the company and they say the pump will easily handle this load for a 20 seconds or less.

 
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#2 · (Edited)
I'm not sure how long you can run double the voltage through that pump before all that wattage becomes a toaster oven but I would strongly recommend you rethink this action.

12v x 10 amps = 120 watts
24v x 20 amps = 480 watts

With the same resistance doubling your voltage will double the amperage which causes the watts to go up 4 times. In this case watts equal heat.
 
#3 ·
Appreciate the input!

I use a 18v “Boost-a-pump” on my other car and have for many years. Boosting the voltage is pretty common in drag racing. Pump health isn’t as much of a concern this application because it is done very briefly. (8 second intervals or less in my case) I'm basically attempting to build a voltage booster box with a $17 battery and a relay instead of spending the $400-700 for the voltage boosting electronics. I suppose I could put some sort of resistor inline to bring the voltage down to 18ish... again I'd need help with that, not which to use.

Would this wiring accomplish what I’m looking to do? Bottom 2 poles would be the dedicated 12/24v grounds.



Here is an example of a commonly used 22v pump booster with a healthy $700 price tag!

JMS P2029PPS11 | Buy JMS FuelMAX Fuel Pump Voltage Booster at JEGS
 
#4 ·
Appreciate the input!

I use a 18v “Boost-a-pump” on my other car and have for many years. Boosting the voltage is pretty common in drag racing. Pump health isn’t as much of a concern this application because it is done very briefly. (8 second intervals or less in my case) I'm basically attempting to build a voltage booster box with a $17 battery and a relay instead of spending the $400-700 for the voltage boosting electronics. I suppose I could put some sort of resistor inline to bring the voltage down to 18ish... again I'd need help with that, not which to use.

Would this wiring accomplish what I’m looking to do? Bottom 2 poles would be the dedicated 12/24v grounds.



Here is an example of a commonly used 22v pump booster with a healthy $700 price tag!

JMS P2029PPS11 | Buy JMS FuelMAX Fuel Pump Voltage Booster at JEGS

If you only had that wiring setup will that work as long as you didn't care about charging the battery. Typically there is a wire from the ignition switch going to the fuel pump. If you put 24 volts to THAT wire then you are putting 24 volts to your entire electrical system.
On a diesel truck the only wires that connect to it are the motor wires so no 24 volts is seen by the rest of the system.
Your fuel pump is a bit different as it has to run whenever the engine is running. You need to disconnect the parallel connection of the two batteries, reconnect them in serial to the fuel pump circuit only, and then disconnect the serial connection and reconnect the parallel connection to charge the battery. You will need more than a single DPDT switch.
 
#9 ·
3 Bosch/Tyco SPDT relays...A, B, & C. Terminal 86 of all relays connected together and to a +12 volt signal to activate system. Terminal 85 of all relays connected to ground. Relay A connections: Term 30, Aux battery negative.. Term 87, Main battery positive.. Term 87a, ground. Relay B connections: Term 30, to fuel pump positive.. Term 87, Aux battery positive.. Term 87a, ignition lead that was feeding fuel pump. Relay C connections: Term 30, Main battery positive.. Term 87, No connection.. Term 87a, Aux battery positive.
Info taken from Jacobs Technical Publications, Doctor's Guide to Automotive Ignition
 
#11 ·
Relay A switches the negative of the Aux battery isolating it from chassis ground allowing it to be connected in series with the Main battery. Relay B switches the positive of the Aux battery to the load. Relay C isolates the Aux battery positive, allows battery to charge in standby.
 
#12 ·
It seems like a bad idea to me to overdrive the pump rather than getting a pump that is rated for the pressure and volume you need.

If you don't mind charging the auxiliary battery manually, you could probably get by using only one SPDT relay and and a SPST toggle switch.

 
#15 ·
Thanks Joe G. That diagram seems sound to me.

I could use a 6v battery in series as well and dumb down the voltage a little if I wasn't wiring the battery into the charging system. :thumbup:

As long as we are just throwing ideas out there... What about eliminating the 12v car source all together? I'd think I could run something like a typical lithium 18v tool battery. (got about 6 of the laying around the shop anyway) They would be light weight, easy to charge and probably more than enough battery for many 8 second bursts?
 
#17 ·
You might want to take a look at the 2nd-to-last paragraph of this FAQ from Aeromotive, and maybe even give them a call to discuss your needs. FAQ – EFI Fuel Pumps – Aeromotive, Inc

If I understand their description correctly, you could get a significant increase in pressure (and horsepower potential) by running two electric pumps in series, and the electrical setup would only require a 12v source. Just power a the 1st pump most of the time, and use a relay to power the 2nd pump only when you need the extra pressure.

Bruce
 
#18 ·
Thanks for the heads up, I'm pretty familiar with that method. I've run 2-3 fuel pumps in parallel and run them in series as well on past projects.

The goal here is one pump and lots of power cheap. These 044 clones AEM put out are work horses. Blasting them with 18-24v for a few seconds really isn't going to hurt them and it pushes the output significantly. One pump on E85 held out to about 17lbs or around 600whp before pressure started dropping and DC went through the roof. I'm looking to run about the same boost on the same engine (5.3 LC9) I have a little larger cam and a more efficient twin turbo setup though so I believe I'll make more power at the same boost.

Using a surge tank and dead heading the rails with the return on the sump. Will be interesting to see how far I get with this setup. Using the OEM fuel tank and pump to fill the surge tank.





Engine shot.

 
#19 · (Edited)
Revisiting this without the relay that has to swap the 2 poles for a seamless transition.

Assuming I had 2 12v batteries. One main system battery and one booster battery. Booster battery is not tied into the charging system. Goal is to get 24v to a fuel pump that normally sees 12v from the main battery. Yet when 24v is supplied it is only seen by the pump and not the rest of the 12v bus.

I found some 12$ 100a diodes and ordered a few to play with. How many diodes would be required to do what I’m wanting in the diagram? Can I do it with one? Or do I need then on both sides? Or is this just wrong all together?
 

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#20 ·
Whole idea is to make it cheap and easy. We are talking under $50 here. Also 24v to the pump will help alot more than 16v. The pumps I use can handle it for short bursts no problem. With diodes in the correct spot it shouldn't back feed 24v to the whole system. Just the pump will see the added voltage.
 
#21 ·
To produce 24v from two 12v batteries, they need to be wired in series. In your last diagram, they are not.

If you would please post a wiring diagram of how your fuel pump is wired now, I would be glad to post a diagram showing precisely how to do what you want to do.

:thumbup:
 
#24 ·
I respectfully disagree. In the diagram in post #19, the batteries are not wired in series, and no point in that circuit would have 24v.

To connect the batteries in series, you wouldn't connect the booster battery to the ground side of the main battery at all, and definitely wouldn't connect the negative side of the booster battery to the pump.

For the batteries to be wired in series, the booster battery negative would be connected to the main battery positive, and the booster battery positive would be connected to the pump via the voltage selector switch.
 
#26 ·
OK I see what your saying now about how I had the batteries in series incorrectly, thanks for that! What about the attached now? Would I just need the lower diode and not the upper?

Appreciate the diagram, but that's very similar to the other ones posted earlier in the thread. I want to go away from using a SPDT relay because it interrupts the signal. I want to use diodes to prevent the bus from seeing 24 volts. Then supply a continuous 12v to the pump and use a switch to activate the second booster battery and 24v. This is also a standard 12v circuit with an alternator in the loop on the main battery. I'm not worried about charging the booster battery with the alternator though.

 
#30 ·
This is what I've done with the relay, except that yours doesn't charge the aux battery. You would need to put a ground on the top right terminal.

Mine can also be done with a dpdt switch, rather than a relay (ignore the coil), but the relay can be closer to the pump, rather than at the dashboard can can probably handle more current.
 
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