Parasitic battery draw with HKB Voltage Booster Fuse

I will double check with an amperage test this afternoon. And I will check the draw again with the booster fuse reinstalled. Thanks for the help!

 

My voltage is definitely boosted by about .5 volts with the "booster" fuse installed.

 

perhaps the booster is more components than just the fuse and diode I was thinking.

 

This but I will clarify that what the "voltage booster" actually does is linearly lower the voltage that the alternator "sees" on the sense circuit to trick it into charging to a higher voltage.

Providing nothing aftermarket is tapped into that circuit it should make no difference what is installed in the ALT-S fuse slot as far as there being a parasitic draw through the voltage regulator.

 

i agree. But for the diode to forward bias it has to draw some current on the series circuit back into the VR. I’m sure It’s minuscule but it is there, ohms law doesn’t lie. The input to the VR should be a high impedance path with ignition switch off so it shouldn’t cause any parasitic draw.

 

Don't you mean Kirchoff's Laws don't lie?

Lol I kid, I kid, I ain't no electrician, just a wise ass

 

If you suspect the HKB fuse is causing a parasitic draw (which it probably isn't just by nature of what it is and how the ALT-S circuit works), then the simplest troubleshooting is to pull it out and reinstall the original 7.5A fuse. Then check if the draw remains.

If not then happy hunting for whatever else is causing it. My money is on either a bad battery or some other aftermarket accessory/wiring modifications.

 

The amperage draw is 0 with a regular fuse installed. I have been thinking bad battery for a while and have had it load tested a couple of times yielding a good result. With a fully charged battery and HKB fuse installed the resting voltage of my battery after 24 hours of sitting will be 12.5. With a regular fuse installed with a fully charged battery and after 24 hours of sitting the resting voltage is 12.6. I am very confident the drain issue is in the alt-s circuit. I am in communication with HKB to see if they have any suggestions.

 

I pulled the HKB fuse to measure amp draw across the Alt-s circuit, the reading is .000 amp. And the amp draw returns with HKB fuse installed (using voltage drop method). Another bit of information is that the voltage will cycle up and down over a couple of minutes in the .2 to .003 volt range on the HKB fuse. Increase, decrease, increase, decrease, etc.

 

HKB confirmed the "boost" fuse is just a fuse with a diode inserted.

 

Your going to read voltage drop across it even if there's just microamps of current going through it due to it being a diode.

Have you checked actual current draw on the battery using an inline ampmeter?

 

I have measured the draw with an inline amp meter. The measurement is about 50 milliamps, which would indicate there is not an issue with a parasitic draw. That is probably the most confusing aspect of the battery drain. 50 milliamps of parasic draw should not drain a battery to 10.5 volts in 2 weeks. I think what I can do is remove the Alt-s fuse next time my truck is parked for a week or so. Then I can verify for certain if the issue is the Alt-s circuit...or not.

Are you saying it is normal for a diode to have some voltage using the voltage drop method?

 

Yes because of how a diode works, @6 gearT444E can probably explain it better than I can but in short there has to be a voltage differential across a diode before any current will flow through it no matter how small that current is. That's how it fools the alternator into thinking the battery voltage is lower than it actually is.

I have seen batteries develop internal shorts and will still test good but rapidly self discharge. You could leave the battery disconnected and see if it's still dead after a couple weeks, that would tell you if it's the battery itself or a drain on the truck.

 

HKB confirmed the diode will show a voltage using the voltage drop method so the HKB fuse is probably working as it should. With that said I may be on the hunt for the vampire still. I will be using my pickup daily for a while so when I get around to it I will check back in with some more testing and results. Thanks everyone for your help!