Need help with a project..any electrical engineers?

I need help with a project I've taken up. Here we have a small desktop water fountain, that sucks up batteries as quickly as it pumps water. The batteries die within two days of keeping it on 8 hours straight each day, and I've decided it's just not worth switching out batteries that often, but I would still like to use it.

Now of course, I could easily go out and spend $30-$50 for a fountain with an AC adapter included, but I figure it's just easier, and cheaper, to modify this one to accept an AC adapter.

I'm pretty sure I can figure out how to wire the electronics and how and where to mount the adapter plug (typically the male receiving end), but I'm not sure how much voltage and amperage to supply it with. I'm afraid of overdriving the motor, but on the other hand, it would be nice if the motor could pump just a little more volume. The fountain takes 2 AA batteries at 1.5 volts each. So am I right in thinking it needs 3 volts to operate? If so, how many amps should it need?

I'm sure one of you engineers can easily figure this one out...........I've included pics below to show you exactly what I'm working with.

Not a big deal to hook it up with an AC adapter, just keep the following in mind:

1. Looks like it's ok to run the pump at higher voltage, say 4.5 V DC. (3 amp?) You might want to make a PWM DC motor speed control (Velleman kits sells them $20,00+-), you can vary the speed of the pump with the control.

2. A DC brush motor generates lots of static RFI thru the AC line to mess up TV and radio receptions, also AC wall adapter is not well regulated, so if you get a 2,000 mf capacitor to go parallel with the motor, the motor will run better and static will be minimized.

3. DC motors are reversible depending on polarity, make sure that you are not runing the pump backwards.

4. last, anytime you are runing 110V AC near water, you need the adapter to be insulated, and grounded electrically, a GFP electric outlet is recommended. ($20.00, you can replace the outlet you have now).

If you get a fish tank screen saver for your computer, it would be lot's simpler :naughty: .

Good luck.

BTW, me, no electric engineer. Is there an engineer in the house?

dcarch8

3 volts

It will only draw as much amps as the pump needs. Seeing how it runs for two days on a set of batteries, I don't think it will draw more than 500ma

http://www.radioshack.com/product/i...Product+Type/Adapters&fbc=1&parentPage=family

yuandrew said:

3 volts

It will only draw as much amps as the pump needs. Seeing how it runs for two days on a set of batteries, I don't think it will draw more than 500ma

http://www.radioshack.com/product/i...Product+Type/Adapters&fbc=1&parentPage=family

Click to expand...

thats the way to go!
if a 3 volt is hard to find just get one of the multi volt units

Thanks for the Rad Shack link, Yuandrew.

There is a cavity in which all the electronics are housed, which allows plenty of room for any additional electronics. Nothing in this cavity comes in contact with the water, only the wire that runs from the cavity to the motor, and that is sealed up with glue. I like the idea of the speed control..that's extra wiring to figure out though.....

You can often find "wal warts" (dc power supplies) at second hand shops, yard sales, etc for a buck. These supplies almost always have the voltage, amps and polarity marked on the case somewhere. Wire your plug so it connects where the batteries were, + to + and - to - . Most wall warts provide at least 300 ma.


According to energizer.com, a AA will have 2800 mah, so the max draw you can have and still have it run for two days (or 16 hours) would be 175 ma.

Daniel

I would suggest a much higher ampage adaptor.

AC adaptors are not fused very well, if at all. Although the pump draws very little current, however, it's the nature of this kind of motor that if it is running normal that it draws little current, under the following conditions, things may be different:

1. Typically the motor has sintered brass bearings which may not last forever.
2. The pump impeller is not filtered and can suck in large particles.

If the motor stalls, the current draw will jump up very high and can easily burn out the wall adapter. If the adapter is high powered, it will burn out the motor instead, which is always under water.

dcarch8

I'm not an engineer and have had little to no training in electronics, but it would seem that the adaptation is relatively simple and can be approached from several avenues.

- Quick, dirty, and ugly way, would be to solder the leads from an AC-3VDC wall wart to the respective battery contacts of the fountain.

- If the fountain will accommodate it, replace the battery holder with one for D cells, you'll probably only need to change the batteries once a month (given a 21 day average business month) A not so pretty alternative would be to connect a battery holder externally and run the wires to the battery holder contacts in the fountain.

- Get kind of fancy and use a coaxial jack that cuts off the battery circuit when it mechanically detects the presence of a coaxial plug (from a AC/DC adapter). This is something that you should be able to find at your local hardware store, an electronics store, or maybe a Radio Shack store.

- Get real fancy, build and incorporate a charge circuit that will recharge NiMH batteries that are used in lieu in the alkaline batteries.

Insofar as current draw, you might be able to get that off of the pump (if there aren't other associated electronics,) but given your description of run time with AA batteries, it sounds like the device is probably drawing less than 100 mAh, so one of the commonly found AC-3VDC adapters that provide 300 mAh would be more than adequate.

I don't think you should have a problem with the wiring, it's just + to + and - to -, just like 5th grade science; I don't think you need any electronics background to figure that out

LaserFreak said:

I'm sure one of you engineers can easily figure this one out...........I've included pics below to show you exactly what I'm working with.

Click to expand...

Brighteyez said:

I don't think you should have a problem with the wiring, it's just + to + and - to -, just like 5th grade science; I don't think you need any electronics background to figure that out

Click to expand...

That much I understand...but most switches and speed controls don't come marked +/-. I can figure it out with a little trial and error, so long as I don't cross - to +...lol. I think I'll just run the leads running between the switch and the battery compartment to the new adapter plug..completely disabling the battery option. Portability really isn't an issue, seeing as I don't EDC my fountain!

I would use a simple adjustable voltage regulator like a lm317t powered by a 5 volt 500 ma wall wart.

5 small parts - very simple

1 lm 317t

1 resistor

1 variable resistor

2 capacitors

if you buy the 317t from radio shack the schematic is on the package.

dcarch8 said:

3. DC motors are reversible depending on polarity, make sure that you are not runing the pump backwards.
dcarch8

Click to expand...

That would really suck! :naughty:

markdi said:

I would use a simple adjustable voltage regulator like a lm317t powered by a 5 volt 500 ma wall wart.
5 small parts - very simple
1 lm 317t
1 resistor
1 variable resistor
2 capacitors
if you buy the 317t from radio shack the schematic is on the package.

Click to expand...

A PWM variable control is a very nice thing to have. In additon to control a motor's speed without loosing power (Torque), It is useful also to control lights (incandescent only).

dcarch8