DC powered tire pump blows lighter jack fuse (20A), works fine w/ another vehicle

[Ichinisan]

My mid-2000s Buick has a 20-amp fuse for the cigarette lighter jack / DC socket. I needed to help someone put air into a tire a while ago and used a pump that is powered by the lighter jack. It blew the fuse for the socket. I had reason to believe the pump was faulty. Apparently it had been disassembled and wasn't fully re-assembled, so something could have shorted inside.

I replaced the fuse with a 20-amp fuse from Auto Zone. For some reason, they didn't have any small packs of 20-amp fuses except the kind that light-up when blown, and it took like 20 minutes to find those.

So yesterday I needed to help the same person put air in the tire (sheesh!). I stopped by AutoZone and bought a pump for $20, then met the person. After 20 or 30 seconds of pumping, my fuse blew again. This person's vehicle doesn't have a lighter jack (it was removed along with a lot of stuff). I still had a couple more 20A fuses from the pack, so I replaced it. After 20 or 30 seconds of pumping, it blew again.

Then my brother shows up with his 5 or 6 year old Toyota and we use the same pump to inflate the tire to 35 PSI.

So the pump is fine. My lighter jack works fine for charging my phone. Why can't it handle a tire pump? I glanced all over the packaging and paperwork and didn't see warning about how many amps it draws.

Is there an issue with these silly light-up fuses?

 

[deadlyapp]

Your phone charger takes at most 10W (roughly 2A at 5V, or something less than 1A at ~12V).

I took a look at the compressor I have : https://www.acehardware.com/departm...oC8JQ1vS96b9OM2srNymbQLhQaGfiVEMaApDwEALw_wcB
But I can find no current draw ratings on it - it only says fused 15A on it - which would be about 180W. There's not a lot of electrical components in these, it's basically just a mechanical device with perhaps some voltage regulation and automatic shutoff on temperature.


I suspect that if you're having this problem with different fuses and with different pumps, your electrical is faulty, or that fuse is having other current drawn from it other than just the cigarette lighter.

 

[C1]

The Occam's Razor explanation is that the problematic tire has a valve stem with restricted air flow. The air pump motor is thus having to work too hard when attempting to inflate the associated tire.

Remember that the current draw of electric motors under load increases. In fact, if the motor armature stops, the motor in effect becomes a dead short due to no current canceling back emf.

Run your air pump from the cigar lighter socket without air volume restriction to ensure it sustains. If so, then while it is still running, take a tool with rag and force stop the air flow to see if the fuse sustains. If not, then you have your answer.

 

[mindless1]

You can either measure what the pump is drawing or test your vehicle electrical circuit with a known 15A load, which is what Autozone's page specs for the only $20 pump I see on their site, made by Slime. It is rated for 15A and "12V" and you didn't mention if you had the engine on so it was at 14.4V-ish instead, but the should have taken that common scenario into account when sizing the motor so it still stayed within 15A as 15A is a VERY common limit imposed on cigarette light powered gear.

I did see an autozone review that mentioned it blew fuses a few times (or was that your review?), maybe the quality control is bad and it is pushing the limits but the other vehicle that had success, has the wrong fuse in the lighter outlet or some generic brand fuse that is not failing at its rated current (which is very common, almost ALL generic fuses are grossly under-spec'd and will pass double or even more current than rated for).

Another possibility is as deadlyapp mentioned, if your engine was on or vehicle in accessory mode, the lighter circuit might be powering other things simultaneously.

The last possibility I can think of is the fuse holder may have corrosion or gunk (hardened electrical grease, etc) on its contacts and the result is resistance there, heating the fuse blade, so it takes less heat originating from the inside to blow it.

If the "silly light up fuses" are not a major brand (like Buss/Eaton or Littlefuse) I would not trust their ratings at all.

Edit: I would trust an OEM fuse so if you have one from a different fuse box location w/same current rating, you might try swapping that in, though if it blows too then you're now down two fuses, and as above I would get major brand replacements.

 

[KentState]

Is that single lighter outlet the only thing on the fuse?

 

[RLGL]

It is possible that there is corrosion in the vehicle wiring harness that is adding to the current draw. This can be any where from the battery to the attachment point of the accessory, positive or negative side.

 

[mindless1]

^ Hate to disagree but no. Corrosion anywhere except on the fuse blade contacts (the fuse box contacts) will be too far away to cause heating of the fuse and that resistance will decrease the voltage and current going through the fuse because the pump is going to have a brushed DC motor (resistive load) and definitely not a voltage boost circuit in it.

This type of motor always uses less current the less voltage it has (unless the torque becomes so low that it stalls)... which is why if it's not blowing fuses, I always run the engine while pumping so it not only keeps the battery from draining but also runs the pump faster on ~14.4V instead of 12.6V. On the other hand if you ask a little pump to run too long at this higher output you can overheat it easier.

If you meant the wiring harness has a fault to the extent it's always shorting out, even without the pump connected there is an extra current drain that shouldn't be there, then sure that could cause this, but I'd think he would notice that separate from using the pump, notice constant excessive battery drain.

 

[RLGL]

^ Hate to disagree but no.

Sorry buddy , been there and done that!