I made a post about having a motor that will not run of 5V. You guys said use a capacitor to start it. I know the motor will run off of the 3V battery (very well) that was inside the electrical screwdriver. So I am going to hook the battery to the motor. Though at the same time I want to charge the battery. So the motor is using the battery while the battery is being charged. I would have to use diodes? If so, where shall I put them.

Thanks,

 

Your car charges its battery all the time you are driving it. Lights are on, gauges are on, and the engine is using electricity to make sparks. Why aren't there any diodes on the car battery?

 

Your car charges its battery all the time you are driving it. Lights are on, gauges are on, and the engine is using electricity to make sparks. Why aren't there any diodes on the car battery?

Fair pont. So do i just hook the 5V DC output of my convertor to the battery and then the motor to the battery?
Or is there another way? Because I did try it and it did not work but thats probably because it was was veeeeeeery messy and the connections were not good.

 

In this case, you have a 3 volt battery and a 5 volt charger. You need a resistor between the charger and the battery to limit charging current. If you don't do that, the 3V battery will load the 5 volt charger down to 3 volts and it will start smoking. The size of resistor depends on how many amps the charger can supply and if it's more than the battery can accept without overheating, the battery has to be the part that determines the maximum current. I have a 50 amp charger for car batteries, but I can't connect that to a AA battery for my camera without a resistor. If your charger can provide 1/10th of an amp and you're charging a 10 amp-hour battery, you calculate for 1/10th of an amp because the battery can accept the whole 1/10th of an amp without smoking.

 

Thanks man!

 

I'm pretty sure your cordless screwdriver motor won't last for long in continuous duty operation.

 

Well let's just hope it does!

 

I'm pretty sure your cordless screwdriver motor won't last for long in continuous duty operation.

I dunno. I have a Makita 9.6V that's pushing 30 years old. It has eaten 4 switches, one clutch and 5 batteries, but the motor is still the first one.

 

Those motors are designed for high torque short duration operation so if you take your 30 years of actual run time and add it up the actual run time hours are pretty low. Probably a few 10's of hours maybe?

 

Well let's just hope it does!

It won't. Especially if it has any load on it. The brushes will be worn out in a day or two of run time assuming the shaft bushings aren't gone first especially if you're running a 3 volt motor on near 5 volts while the battery is charging.

If you need long term running use the right motor for the job.

 

Probably a few 10's of hours maybe?

I think the 4 switches is a defining number for wear and tear. They don't break every 10 hours.
I worked professionally with that drill for most of those 30 years. Mostly screws in and out of sheet metal, but I built some outdoor structures with wood and Tapcons. I remember one day I emptied a nice, new battery in 4 hours doing screws into PT lumber. I think the real number is in the hundreds of hours.

Then again, a 3 volt screwdriver is nowhere near the quality of a Makita 9.6

 

Perhaps but how they built them 30 years ago doesn't represent anything of today and a few hundred hours isn't all that long in continuous run time terms. Not much more than two to three weeks.

I just did my fall furnace check and clean last week and ~ 6 - 7 years ago I had to put a new blower motor in so I installed a hour meter on it just for curiousity sake. Right now it's at ~19,000 and some hours putting the ~35 year old furnace running life at a good 100,000 or more.

 

If the motor stops using power for whatever reason, but the charger keeps going, eventually the battery will be full and the charger will over charge the battery. Since the charger is capable of supplying more voltage than the battery is rated for, you need some way to stop the charger when the battery is full. A resistor will reduce the voltage while current is flowing, but as the battery fills and the current reduces, the voltage will increase.

 

Us knowing what the motor is being used for would be helpful.

 

I am going to hook the battery to the motor. Though at the same time I want to charge the battery. So the motor is using the battery while the battery is being charged.

If the motor stops using power for whatever reason, but the charger keeps going,

It's important to design for unintended uses.

 

Us knowing what the motor is being used for would be helpful.

Sorry for the extra delayed reply, it is going to be used for some sort of table saw so it won't be on continuously.

 

it is going to be used for some sort of table saw

A 3V motor for a table saw? Are you making toothpicks?
I had to put a 5HP motor on my table saw because it cut 14 hours off one job, then continued to work to this very day.

 

Sorry for the extra delayed reply, it is going to be used for some sort of table saw so it won't be on continuously.

I've got mini saw blades that go on my dremel and even at 120 watts on line power it's pretty useless for anything but thick paper.

 

Your car charges its battery all the time you are driving it. Lights are on, gauges are on, and the engine is using electricity to make sparks. Why aren't there any diodes on the car battery?

Not really that simple. No load is connected directly to the battery except the starter motor, and that is used only for starting the car.
You have a separate system monitoring the battery charge current and the voltage is not a steady 12 volts. It can go up to almost 14+ volts.

 

Not really that simple. No load is connected directly to the battery except the starter motor, and that is used only for starting the car.

What?

In my vehicles everything is connected to the battery when the ignition is on.