I'd like to repair a WaterPik, a device that shoots water at a relatively high pressure onto gums (of the mouth). The purpose of this device is to strengthen and clean the gums.

The unit has a 2.4V 1300 mAh battery that is charged with an AC adapter. I've charged the unit according to the instructions for 10+ hours, but the the battery seems drained (at one point, the motor started just barely, so it seems it's not the motor). Nothing happens now when I turn the device on.

I disassembled the unit and measured a 2.4 voltage across the battery terminals. I did not get a current reading. When a battery is drained, I'm assuming that there's still a voltage, but no current. Is that correct?

If it's the battery, then I assume I should just find an identical battery. Where would I find something like that?

Please see the attached photo.

Thank you for your help!

 

When a battery is drained, I'm assuming that there's still a voltage, but no current. Is that correct?

There might be a voltage under no-load conditions, but as soon as you turn the motor on the voltage would decrease dramatically. Can you check this?

Voltage of the battery when the load is applied?

 

Obviously the case has had some moisture intrusion that's caused some corrosion. This may be enough to disable the unit.
Other troubleshooting steps:
Battery voltage available? Switch continuity and resistance? Motor condition?
You can load test the battery with a 10Ω 1W resistor (≈240mA load). If you need it, Batteries Plus can sell or make you a new battery pack. There are two stores in Portland. It should be less than $20.00 if you unsolder the original and take it in.
http://www.batteriesplus.com/store_locator/state/OR.aspx

 

The water damage/corrosion aside, the battery pack having been charged for 10 hours and reading only 2.4V is either of two possibilities. 1) The charger doesn't work. You could measure the charger voltage. I suspect it's around 3.0V. 2) The batteries have had it. This is what I think is your problem. Fully charged, the battery pack should have a voltage of around 2.8V - 2.9V. They appear to be two NiCad types in series, you can often find these at Radio Shack, local drug stores, or even Wal-Mart. They shouldn't even cost you as much as $10.

You cold first verify that the motor still runs by connecting a 3V DC supply to the motor.
+ (red), - (black).

 

I'm betting they stuck NiCd batteries in the thing and the batteries are shot. Take the thing to a battery store and they can probably fix you up. You can also check Radio Shack, as they have NiCd batteries in common sizes; I've fixed a few of my wife's appliances by putting in new batteries.

Technically, they're called "babbilies" at my house -- my youngest daughter said that when she was 3 or 4 years old. She got over it in a year or two, but a typical parent thinks it's cute and will use it till the day they die. So tell all the young kids that this is a great way to get back at your parents while you're still young! Don't wait for the teenage years! I use that word in a conversation and I get the look "Oh, would someone please interchange grandpa's IV bottle and catheter drain bottle again?".

 

One more vote for the water damage...........A water appliance after all............

Beauty of it is, those little motors are repairable if you have that level of insanity [[ btdt ]] or there are a million or so hobby motors available.....you shouild be able to match it somewhere.

 

I guess the proper game plan would be this:

1) Measure the chargers voltage and note it's voltage output. It should be close to 3V, maybe even higher.

2) Take out the battery pack, since you will have to either to replace the motor or to replace the batteries. Test the motor with a 3V DC supply, using 2 charged AA nicad's, NiMH, or Alkaline batteries connected in series. Note if it is good or bad.

If the charger is O.K. and the Motor is bad, find a suitable replacement for it. after replacement, I'd also recommend replacement of the batteries as well or you will find yourself opening the unit up again sooner than you think.

If the charger seems O.K. and the Motor seems O.K. then replace the batteries with new NiCad's. The AH rating on the battery in not important as long as it is equal or larger than what was in there.

 

Thank you all for your input. I really appreciate it.

The battery is a NiMH one.
Ionic, your game plan sounds solid. I got stumped on the first stage. It's hard for me to measure the voltage of the power adapter, because the female holes are narrow and long - not able to properly put multimeter leads in there. I wouldn't suspect that the power adapter is at fault, but it's likely I'm missing something.

I'm a total amateur in electric appliances. Is a desoldering iron necessary to take apart the motor and the battery? Besides Radio Shack, where is a good place to get one?

Thanks for the help!

 

Thank you all for your input. I really appreciate it.

The battery is a NiMH one.
Ionic, your game plan sounds solid. I got stumped on the first stage. It's hard for me to measure the voltage of the power adapter, because the female holes are narrow and long - not able to properly put multimeter leads in there. I wouldn't suspect that the power adapter is at fault, but it's likely I'm missing something.

I'm a total amateur in electric appliances. Is a desoldering iron necessary to take apart the motor and the battery? Besides Radio Shack, where is a good place to get one?

Thanks for the help!

A paper clip in the center hole of the power supply might help you read that voltage.

You don't need a desoldering iron just a cheep soldering iron and some solder.

 

iONic,

Well, I get no reading when I test the power supply separately. I guess it may be at fault.

Should I try to find an adapter with a similar rating?

As an aside, I noticed that the power supply is not an AC adapter - it converts 110 VAC to 3VAC at 100mA.

This is thoroughly confusing me, because as the picture shows, the wires feed into the battery. How can the adapter output AC power to charge the battery?

Thank you.

 

iONic,

Well, I get no reading when I test the power supply separately. I guess it may be at fault.

Should I try to find an adapter with a similar rating?

As an aside, I noticed that the power supply is not an AC adapter - it converts 110 VAC to 3VAC at 100mA.

This is thoroughly confusing me, because as the picture shows, the wires feed into the battery. How can the adapter output AC power to charge the battery?

Thank you.

Looking at the photo you posted, I suspect there is a rectifier (or 2) in the lead that goes from the adapter socket to the +ve terminal of the battery. It looks like there is a component under the heatshrink.

 

I see that too. It's probably a diode and a resistor.

 

iONic,

Well, I get no reading when I test the power supply separately. I guess it may be at fault.

Should I try to find an adapter with a similar rating?

As an aside, I noticed that the power supply is not an AC adapter - it converts 110 VAC to 3VAC at 100mA.

This is thoroughly confusing me, because as the picture shows, the wires feed into the battery. How can the adapter output AC power to charge the battery?

Thank you.

You would get no reading if your multimeter was set for DC and the adapter output was 3V AC. Did you switch to AC and try it??? !!

 

PeeSeeBee, KJ6EAD, Ionic,

Thank you for your input.

Yes, indeed the voltage goes up to 2.9 V briefly when I switch into the AC mode, so the adapter seems not to be at fault.

The fact that it doesn't stay at 2.9V is a reflection of the intermittent nature of the AC voltage, correct? If so, I still don't understand why it doesn't keep jumping back and forth. The multimeter will show a voltage of 2.9 for a second and then revert to 0 without further changes.

I do have trouble getting an AC current reading from the adapter leads (the adapter output is rated at 100 mA).

I will now proceed with testing the motor and the battery as Ionic had suggested.

Cheers!

 

PeeSeeBee, KJ6EAD, Ionic,

Thank you for your input.

Yes, indeed the voltage goes up to 2.9 V briefly when I switch into the AC mode, so the adapter seems not to be at fault.

The fact that it doesn't stay at 2.9V is a reflection of the intermittent nature of the AC voltage, correct? If so, I still don't understand why it doesn't keep jumping back and forth. The multimeter will show a voltage of 2.9 for a second and then revert to 0 without further changes.

I do have trouble getting an AC current reading from the adapter leads (the adapter output is rated at 100 mA).

I will now proceed with testing the motor and the battery as Ionic had suggested.

Cheers!

Way to go!
The DC readings will bounce around, so I wouldn't rely too much on how it is reacting. The Adapter should be steady 2.9V on the AC setting. Your doing it right, test the components before you invest in parts.

 

Looking at the photo you posted, I suspect there is a rectifier (or 2) in the lead that goes from the adapter socket to the +ve terminal of the battery. It looks like there is a component under the heatshrink.

Yes, and thus there really is no charge regulation other than the supply voltage itself and 1.5V/cell is a tad high. If one battery weekends you'll kill them both in no time, the second one from overcharging.

After paying $100 for a Sonicare toothbrush some years back the batteries became useless surprisingly fast. The trouble there was that they left you no way inside to replace the batteries other than to Hack yourself in. So after a few years and $100 down the tube, I did some hacking and placed to NiMH AA's inside and left a door latch so I could manually charge them in a good charger as apposed to the induction charge method they used, which was probably unregulated. The battery pack was literally glued to one side of the casing! No, No, No they said! ...byte me I said. Enough of this planned obsolescence.

 

...the voltage goes up to 2.9 V briefly when I switch into the AC mode, so the adapter seems not to be at fault.

The fact that it doesn't stay at 2.9V is a reflection of the intermittent nature of the AC voltage, correct? If so, I still don't understand why it doesn't keep jumping back and forth. The multimeter will show a voltage of 2.9 for a second and then revert to 0 without further changes...

If you have set your meter to measure AC volts, you should get a constant reading on the meter. It shouldn't show a reading for just a second, then revert to zero, it should be continuous. Is there a problem with your meter?

Do you have a spare rectifier diode handy? you could try slipping one end of it (the end without the band) into one of the sockets of the 3v ac output, then, with your meter set to dc volts, put the black lead into the other socket & the red lead onto the banded end of the rectifier.

If you haven't got a spare diode, measure the voltage across the battery, then plug the adapter in & measure the voltage again. It should go up when the adapter is connected. If you have bought your soldering iron, you could try desoldering the black lead from the +ve side of the battery (that comes from the adapter connector) & measuring between the battery -ve & the wire you have just unsoldered. Assuming that there is an in line rectifire in that lead, you should get a dc reading when the adapter is plugged in.

...I do have trouble getting an AC current reading from the adapter leads (the adapter output is rated at 100 mA)...

I hope you are not connecting your meter set to read current across the output of the adapter! You will short out the adapter & could damage your meter!

 

After paying $100 for a Sonicare toothbrush some years back the batteries became useless surprisingly fast. The trouble there was that they left you no way inside to replace the batteries other than to hack yourself in.

I had one of the older ones with a more cylindrical body and was able to rebattery it by cutting the case open cleanly with a roller type pipe cutter. The impressive cutaway view on the package showed me where to cut and the advertising for the product bragged that it was made of Cycolac so I knew I could glue it back together with ABS pipe cement. I was able to sand and polish the glue line so the result was just an extra black stripe on the body.

 

Thanks everyone for your continuing help!

If you have set your meter to measure AC volts, you should get a constant reading on the meter. It shouldn't show a reading for just a second, then revert to zero, it should be continuous. Is there a problem with your meter?

I rigged up a way to fixate the pins I put into the AC adapter holes and was able to get a constant reading on the meter.

If you haven't got a spare diode, measure the voltage across the battery, then plug the adapter in & measure the voltage again. It should go up when the adapter is connected.

The voltage does not go up when I do this. Since we established above that it's not the adapter that's at fault, maybe it's the wires between the battery and the adapter.

Examine the picture below. The left wire does seem to be chewed up a bit, though it looks like there's still contact.

I hope you are not connecting your meter set to read current across the output of the adapter! You will short out the adapter & could damage your meter!

Would this short out the adapter because the neutral lead isn't designed to carry so much current? I'm confused.

Why would the meter be damaged, I thought it's designed to measure high currents?

How would I measure the current coming out of the adapter?

 

Hi Roma,

Meters measure voltage by putting them in parallel with the power supply, in other words, you put it across the supply leads, in this case, the two leads of your adapter.

To measure current, the meter has to be put in series with the circuit. You cannot measure current across a power supply, only in series with the load. If you have no load (no circuit or nothing drawing power), there will be no current.

When a meter is in current mode, the leads are, in effect, shorted because the measurement is different from that of voltage. Trying to measure current by putting the meter leads across your supply (like when you measure voltage), is equivalent to putting a wire or paperclip across the leads - it creates a short and can damage your supply, your load, your meter, and maybe you.

If you want to measure current, you can only do so by putting your meter in series (and in the proper orientation) between one of the adapter leads and the adapter connector. Since this is AC, you shouldn't have to worry about orientation. As this is such a small current supply (100mA), as long as you're seeing ~3VAC, it is a safe assumption the adapter is working.

I suspect the charger is frying your batteries - these are cheap, simple chargers. They run constantly and rely on you to only have them plugged in for x hours. If you leave them plugged in beyond what they need, they'll overcharge then damage the batteries.

I'd recommend removing the batteries and taking them to a local battery shop to have them checked out. In the U.S., BatteriesPlus can do this, not sure elsewhere.

Ultimately, if you want to avoid this problem in the future, either make or buy a smart two-cell (2.4-3V) battery charger that will let you know when the batteries are fully charged (which should have circuitry to recognize this and stop charging the batteries).

If you have a good rechargable battery charger, these typically work with two batteries at a time and you could charge your waterpick battery on that (make sure the chemistries match Ni-Cd vs. Ni-MH) and see if they still work for as long as you expect.

Hope this helps.