I picked up a few 6v Autopulse 500 pumps recently. In order to tie them into the 12-volt system on the car, I decided it would be a great idea to use one of those cheap ceramic resistors that are advertised for use in old Ford tractors, I think they are ignition coil related. Anyway, I tested the pump on 12 volts real quick and it sounds like a jackhammer, so I wired it up after the drop-down resistor and all is quiet. It looks like I'm getting like 2.3 volts after the resistor, which is obviously not going to work. I didn't have a lot of faith in that part, and it let me down anyway. Is there a cheap/good/easy way to ensure I can step the voltage down properly to avoid burning up the pump? At first I wanted to make sure things were period-correct-looking, but I ended up mounting the pump in between the cowl tank and the firewall on the inside of the car, so nobody will see whatever the solution for this ends up being. I realize the best solution would be to just buy a 12v pump, which I would have done if I knew how deep this pump was going to get buried in the car and if 12v Autopulses weren't so expensive.
When you use a dropping resistor, you have to match the resistor to the load. If they don't have the same resistance, it won't drop the voltage in half...it will be some other fraction. You might try an electronic voltage reducer, either a regulator or a "buck" DC-DC converter. But you need to know the current draw of the pump, to get the right type.
Thank you, I didn’t know any of this. Should the current draw measurement be taken when it’s operating at its intended 6 volts, or at 12? It looks like finding a correct buck converter shouldn’t be too hard once I know the amperage of the pump.
Must be measured at 6 Volts. It will be hard to take an accurate current measurement if this is a pulsed device (i.e. the internal electrical mechanism rapidly switches on and off). Side note: Digital voltmeters do not work well with pulsing voltages. The old fashioned analog (dial gauge) voltmeters will give you an average voltage. Russ
Thanks guys. Yes, this is a pulsed pump. I'll report back with what I find and what I do based on the readings.
it'll be really difficult to get a current measurement. See what kind of DC-DC converter you can find that's rated for perhaps 20 amps or so...it might be enough, it might not.
Here's a 20A converter that looks like the right specs. That's a lot of current, is that really how much one of those pumps might draw, or is that for the sake of not burning up the converter? https://www.amazon.com/uxcell-Conve...ref=sr_1_7?keywords=12v+dc+to+6v+dc+converter
the pump has an electromagnet in it, and it takes a lot of current to make one of those get going. And beware that an electronic power supply might be damaged by the back-current when the magnet shuts off (the magnet cycles on and off, which gives the pulsing effect that makes it pump fuel) It's really a good idea to use a pump that's the same voltage as the car's electrical system. You can try the converter and see if it works, but beware that it might not.
I have found those old 6V Walbro pumps to be very prone to failure as the rubber diaphragm gets dissolved by the fuel. They are not dependable and do not have a long life. They fail without warning and then leak gas like a sieve pumping out raw gas. Save yourself future headaches and go with a modern 12V pump. A 6V pump in a 12V system doesn't make sense.
A blocking diode could help, but in the end it is a "Mickey Mouse setup" to justify using what is already purchased @Tumblin' Dice Sell the Autopulse to the VW crowd and buy a correct 12v would be cheaper. I doubt whether these old pumps could handle modern ethanol "Jungle Juice" without leaking @Tumblin' Dice If that pump was drawing 5 amps it would require a 1 ohm resistor rated a 30w If that pump was drawing 4 amps it would require a 2 ohm resistor rated a 24w here is an online calculator https://elecurls.tripod.com/drop-res.htm
Thanks, everyone. I really appreciate all the expertise. For some reason I did not suspect this would be that big of an issue. Ignorance is bliss, right? I agree I don't want to be doing any weird electrical gymnastics (or throwing good money after bad) to get this to work correctly. That first resistor I tried was 5 ohms, so it makes sense to me that there wouldn't be enough voltage downstream from there, I guess. Long-term, a 12v pump is going to be the solution for sure. That said, these old Autopulses with the copper bellows are apparently pretty reliable once they've been sorted out. @Hitchhiker is the Autopulse guy, he might have something to say about all of this. Whatever I end up doing I'll report back.
About all I can add is that autopulse pumps were also available in 12 volt. And with the copper bellows there is really no concern with modern fuels. I'd say the biggest complaint is they are LOUD.
A "old walbro pump to be very prone to failure" really has no bearing, as when they were branded autopulse they were copper bellows. Which are impervious to fuel. There is some rumor that some of the later pumps had rubber bellows. But I have yet to see one in any of the Autopulse pumps I've had. Once they went Walbro. The rubber is a huge issue and I wouldn't bother with them either.
you might also measure the resistance of the coil in the pump, but note that it's really an inductive load, not a resistive load, so that may or may not help.
I’d just use a 12v pump. To measure current you need to be in series with the load, inductive DC current meters can get pricy. Also, the use of an analog meter is best to get an idea of what it draws when first tuned on. The cost of a 6v car battery would exceede the cost of a 12v pump.
Check fleabay these are 10a so you could put 2 parallel https://www.ebay.com/itm/3156553097...8mUtOCRc6j3QB9F0g==|tkp:Bk9SR_b545q7ZA&edge=0
A series resistor will drop voltage relative to current. See Ohm's law. For mine, I built an LM338 voltage regulator to get 6V. This style is rated to 5A and works fine for me. The car had the fuel pump when I got it, and I needed a way to keep it when I did the 12v conversion.
I really wish people would stop calling basic resistors voltage reducers, voltage regulators and such. Yes, if you run a current through them the voltage will drop, but the drop will be proportional to the current and you'll only get the "correct" voltage drop at one specific current - at less current you'll get too high voltage and vice versa. That may be plenty good for something that consumes a fairly stable current, such as a light bulb, but way, WAY off for something that can consume different current depending on load, such as anything with an electric motor. On top of that, in that ebay ad they neglect to mention that that type of resistor needs to be mounted to a big cooling metal surface to be able to handle anywhere near full load. Putting it inside a fan duct will help, but probably not enough for handling max load. Especially if the car belongs to someone who doesn't use the fan all the time.
This is the way to do it, you can adjust it for spot on 6v. You also have a bit of extra current capacity if you need to run any other 6volt stuff. Dropping resistors are all good, but you need to know what the current draw is at 6volts, then calculate the resistance and wattage rating from there, and the resistors will always run hot.
Let me preface this by saying use a 12 volt pump. But, this should work. I’d wire it through and ammeter and have the pump drawing fuel to get an idea of the current draw before installing in the vehicle. Also no idea of cooling requirements needed, etc. https://www.ebay.com/itm/2563735491...MImoKsi5e4iAMVbiKtBh0IOwckEAQYBCABEgIHOPD_BwE Edit: let me add, you’d want to find out if the above is okay for a continuous run. I’ve never used an add on electric pump, re-reading above, you may need one for 20 amp service.
Thanks everyone for all of the comments, I finally had some time to work on this again. I wired up a 12v-6v 20A linear regulator to see how it would go. Obviously, after the regulator I was reading 6v as intended and the pump seemed to be operating normally. Couple comments, though... You guys are right, it is impossible to get a current measurement with a digital meter on these pulsing pumps. I am not sure what it looked like while the pump was under load Also.... I was thinking the correct voltage would quiet this pump down. It still sounds like a jackhammer. How do you Autopulse people deal with that constantly??? That would not be of assistance on date nights driving back from dinner with the wife. So, I think I'll end up picking up a different pump just based on the noise alone. But that's a different thread...
Mount it near the tank on resilient mounts. (Great if you have a 19' Caddy, but in an A or 32 you might need earplugs).
Depends on what mood the "jackhammer" is trying to put her in. For any electric pump [including those noisy "facet" pumps] I've found that USED soft "almost perished" rubber anti--vibration mounts used on car A/C condensers are the quietest. I usually grab a few from the local "Pick-A-Part" New Anti Vibration mounts aren't as good as used
This would work. Just remember that there is no metal running through these, only rubber… I change these often on industrial controls that aren’t even on a moving part. For that reason I would run some kind of leash to the pump to make sure it can’t be overly liberated if the rubber mounts break.
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