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Dust Buster Charge Regulator/Rectifier Help.

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So I'm working on this battery-powered vacuum that recently died. I diagnosed it as one of the magnets breaking loose and a burned out wall wart charger. I fixed the magnet and the motor works now, but the wall wart has an output of 15v, and I only have a 12v wall wart. I tried, but the way the Charge Regulator/DC Rectifier works will not allow it to charge unless it's 14+ volts, and it doesn't cut it. The question I'm asking is is there any way I can change the resistor values to allow this unit to be charged using 12v? I don't want to go buy a new wall wart. I have advanced soldering skills and moderate electronic skills so I'm well able to handle modifying this, but I just couldn't figure out what would work. Follow this link and there is a schematic posted as well as pictures of the circuit. Please ignore the wire colors, they may not be correct. It is a very straight forward device. Please take a look and let me know!! Thanks!!

G's Pic-Host

P.S. If you don't know what a wall wart is, it's a power supply that plugs into the wall. Like a cell phone battery charger.
I get "page not found" viewing the pic.

What voltage is the battery pack in your dust buster? If it's 6 or 9V, it may be possible to modify the regulator to work from a 12V wall wart. But if it uses a 12V battery, you're going to need 14V to charge it, and at least 15V to get 14V from the regulator circuit.

Your best bet is to buy a new wall wart. Or a new dust buster.
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The 3 diodes each drop 0.6V or so, so the battery pack and 2Ω resistor combination receives 13.2 volts total from the original 15V wall wart. Some of that voltage is dropped across the 2Ω resistor to provide the charging voltage with current limiting. Without knowing the amount of resistance the battery presents to the circuit I can't calculate the actual voltage or current, but let's say that the pack charges at 300 mA. R=E/I so 13.2/.3 = 44 ohms (42Ω for the battery pack and 2Ω for the resistor). The voltage across the battery would thus be 12.6V and the resistor, 0.6V.

The most you can eliminate are 2 of the diodes, as you need 1 to prevent the battery from discharging through the wall wart if it's unplugged. That will gain you 1.2 volts. Reducing the resistor value can give you back another 1/4-1/2 a volt or so. So, to get the same rate of charge you would need at least a 13.2V wart. A 12V might work since they often put out a higher (open-circuit) voltage than what they're rated for.

One way to find out if it works is to connect a multimeter in current (milliamp) mode in series with the battery pack and charger, short out 2 of the diodes and connect it to your 12V wart and see how much current flow you get into the battery. If it charges at say 50mA or more, you should be ok.
This may be a somewhat stupid ? here, but are you looking for a 15 VAC Output wall adapter or is it a 15 VDC Output?

fixed my DustBuster


Thanks for the images and circuit diagram.

My 15.6V Dustbuster was not charging. I did not want to be part of a throw-away-societey, so I purchased a new battery from the repair shop on their recommendation. After replacing the battery, it still did not charge.

So I checked the charging circuit, and the 10Ω resistor (yours is 2Ω) in serial with the diodes was open/broken. I replaced the resistor, and the battery is charging again, but the LED does not turn on when charging.

I don't remember if the Dustbuster came this way, or was damaged when I dropped it.

Would someone please explain the circuit for me? This is not a bridge rectifier. Is it a pulse charger?


Unless I’m looking at that pix of your Dustbuster batt pack (the part in black plastic) the wrong way - you are saying that the batt pack is only a 9.6-volt (as in 8 Ni-CD cells), but yet your wall adapter is said to be a 15-volt (AC I guess - as you still haven’t clarified that part). It would indeed appear to be AC - as by your Charge Pulse circuit schematic you had posted.

In looking at that pix of the black batt pack it somewhat appears that it might be at least a 12-volt (10 cells) or possibly even a 14.4-volt (12 cells) batt pack, but it’s hard to tell just looking at that black cased pix, as the black batt plastic case makes it look kind of deceptive. The latter 14.4-volt you can all but rule out, but the 12-volt you can’t.

Reason I say that is because I sell 12-volt AGM batt float chargers esp spec’d out at 13.5 volts for any 12-volt VRLA batt (AGM or GEL cell), as well as for all 12-volt FLA batts such as standard car batts, and Deep Cycle batts. The wall adapter part is outputted at 15VAC @ 600ma max output, and the DC charge chip brain part is limited to 500ma at a perfect 13.5 volts max.

Again - a bit more complex (sophisticated) then your simple 3-diode series pulsed DC current circuit you have there. That’s why I think the ~13 volts DC across your 9.6 volt batt pack seems a bit high! At full charge your batt pack would be at 11.2 MAX is why. Whatever the charge LED pulls through the batt pack at full charge is less then 60ma anyway. Probably it’s closer to 20-25ma if you measured it series wise IN CIRCUIT.

That’s hoping that those 2 & 12 ohm resistors are to spec!

If I had to bet money on it I’d say it’s a 12-volt DB, as that makes more sense as to the charge circuit and it’s float voltage. If it is indeed a 9.6-volt DB then I guess they figured in a faster charge rate, which also heats the batt pack a bit more as well. Shorter life span is all that way!

Have you physically taken the black batt case apart to check each batt call separately? If you haven’t you might be fooling yourself!

Is the actual batt pack voltage stated on the batt pack anywhere, or on the DB itself as to the real batt voltage of the batt pack? Somehow I can’t see the batt pack only being 9.6 volts. Not when the charge circuit is set up to float the batt at roughly 13 volts after being fully charged.

As for (dhoke) and what you added about getting somewhat ripped off on having to buy a new batt for your 15.6-volt DB when it really didn’t need one - as related to that broken 10 ohm resistor - that coming after the fact as it were! At least it is charging fine now! Too bad you didn’t catch that bad 10 ohm R sooner.

As for your Power ON LED there not working - you said that you dropped the DB at some point? Was that charging problem right after you dropped the DB as well or was the dropping part and the LED after you repaired and R&R that bad 10 ohm R??

It’s possible that you broke the LED’s current dropping R as well. That or you may have even cracked the PCB and caused a loose solder connection - as to the LED or R or both. If the LED was exposed to being above the DB’s case and somewhat stuck up and out a bit, and it was struck - when you dropped it - then it’s possible you just broke the LED itself at one of it’s 2 leads internally.

They are easy to test out - as all you do is use the DIODE test setting (roughly 1.5 volts DC) on your DVM, and then touch the probe leads properly to bias the LED, and if it lights up then the LED is good, but the current dropping R may not be.

Other then that I doubt DB puts much of anything sophisticated into their small cordless vacs. Pretty down and dirty cheap by design. I ran my older 6-volt DB model for over 15 years until the original Ni-CD batt pack died one day, and then I just rebuilt it for $4 with 4 surplus Ni-CD batts, and it lasted me another 10+ years and then the motor windings shorted from old age. For a $3 garage sale item I got my moneys worth out of it.

Now I just use my Ryobi 18-volt model C/L hand vac that I got for free. When Ryobi first came out with those multi tool kits there was such an abundance of their vacs that people were practically giving them away. I just traded for mine as that is how I got it for free. Otherwise they can be had for $15 on Craigslist. The Ni-CD batt packs are pull out type and they are 1 hour charged with their great base charger. Very well designed and built charger I might add!! They too can be had for like $10 on Craigslist as well.

Anyway - let us know if you find out what is wrong with that charge / Power ON LED there??

Best regards,

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