Dc voltage from a 9v battery and 9v from mains.

Thread Starter

Bod

Joined Sep 18, 2016
317
So I got this big bulky motor out of a 4x4x4 American RC Monster truck (Runs off about 7.2v DC). I hooked it up to a 9v battery worked fine. So I hooked it up to 9v DC converted from 230/240v AC. And it just turned on then off the on then off repeatedly. Is this something to do with different currents or amps or something like that?
 

Papabravo

Joined Feb 24, 2006
21,157
So I got this big bulky motor out of a 4x4x4 American RC Monster truck (Runs off about 7.2v DC). I hooked it up to a 9v battery worked fine. So I hooked it up to 9v DC converted from 230/240v AC. And it just turned on then off the on then off repeatedly. Is this something to do with different currents or amps or something like that?
It sounds like you have something other than 9 VDC from your converter. Can you measure it with a DMM or an oscilloscope?
 

crutschow

Joined Mar 14, 2008
34,280
Sounds like the current rating of the 9V converter is insufficient.
Do you have a multimeter to measure the motor current when connected to the battery?
 

Thread Starter

Bod

Joined Sep 18, 2016
317
I measured it and the voltage i got was 9.05 V exactly and the thing is, I don't think there is something different because everything else i used that needed 9V worked fine. Its just the motor that does not. There are some photos of it (sorry one is sideways

IMG_0041.jpg IMG_0042.jpg IMG_0044.jpg
 

Thread Starter

Bod

Joined Sep 18, 2016
317
When the motor is hooked up to the battery its current is 2.15 - 2.20. Also I would not say it's insufficient because it's a genuine BT (British Telecom) power adapter and every thing else that needs 9 V runs fine off of it.
 

wayneh

Joined Sep 9, 2010
17,496
Just to be clear, you just said the current was 2.2 amps. Is that what you meant, or is that voltage? Your other post was 9.05V, was this under load or no?

When you say the motor ran fine off a 9V battery, do you mean one of those little rectangular "transistor" batteries?
 

Thread Starter

Bod

Joined Sep 18, 2016
317
I meant 2.2 amps because @crutschow asked me what the current was. Pretty sure it was under load and yes one of those 'little rectangular transistor batteries'.
 

MrSoftware

Joined Oct 29, 2013
2,188
Connect your volt meter to the motor while it's connected to the wall adapter. Does the voltage drop significantly when the motor is stopped?

It's possible the motor is drawing more power than the wall adapter can support, and it's possible the wall adapter has a protection feature that turns it off in this case. Eventually it resets and the motor starts again, and the process repeats.
 

Thread Starter

Bod

Joined Sep 18, 2016
317
Connect your volt meter to the motor while it's connected to the wall adapter. Does the voltage drop significantly when the motor is stopped?
I sort of think so. The amps peak at 0.15 when the motor is on. When it turns of it drops to 0.00 amps.

I could change to to 12 V DC if you think that 9 V DC is not enough. But I won't go much higher as the whole RC Car (and the motors) runs of a 7.2V Li-Po battery.
 

Thread Starter

Bod

Joined Sep 18, 2016
317
I think I found the problem, but thanks for all the help anyway! It's that my power supply is 'feeding' the motor 9V DC and 0.65 amps. When you hook the motor to a 9V battery you can see the max amount of amps it draws which is 2.2X (x = a number I don't know). So if you do
0.65 - 2.2x = fail safe! and the motor resets. :(
 

blocco a spirale

Joined Jun 18, 2008
1,546
I think I found the problem, but thanks for all the help anyway! It's that my power supply is 'feeding' the motor 9V DC and 0.65 amps. When you hook the motor to a 9V battery you can see the max amount of amps it draws which is 2.2X (x = a number I don't know). So if you do
0.65 - 2.2x = fail safe! and the motor resets. :(
Didn't you read post #3? Crutschow (and everyone else that replied) beat you to it.
 

ian field

Joined Oct 27, 2012
6,536
So I got this big bulky motor out of a 4x4x4 American RC Monster truck (Runs off about 7.2v DC). I hooked it up to a 9v battery worked fine. So I hooked it up to 9v DC converted from 230/240v AC. And it just turned on then off the on then off repeatedly. Is this something to do with different currents or amps or something like that?
Those things still use Ni-Cd cells because Ni-Mh can't handle the current draw - your wall wart probably can't either.
 

Tonyr1084

Joined Sep 24, 2015
7,852
I didn't know a 9v transistor battery could deliver 2.2 amps.

When one assumes the power supply is capable just because of its name - one learns a lesson. Your wall supply isn't capable of delivering that much current.

And a Li-Po battery is capable of delivering a whole lot more current than a 9V transistor battery. (the rectangular battery with snap buttons on the top).

The dumbest question is one nobody asked. However, when a question is answered, the second dumbest thing is to not listen to it.
 
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