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12v battery/transformer question.

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cbiblis

New Member
Can anyone please tell me why this circuit will run perfectly on a battery, but will not work on a full bridge rectified transformer?
 

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Dick Cappels

Active Member
One guess is that the voltage source's internal resistance is too high. Try using a regulator between the bridge and the circuit.
 

cbiblis

New Member
What do you suggest for a make shift regulator. I have lots of components but am to new at this to guess which to use.
 

kchriste

New Member
Forum Supporter
Couple of questions:
How large is the filter capacitor after the bridge rectifier?
What is the VA rating of the transformer? (VAC and AC amps)

You are drawing motor current through D5, a 1N4148, which can handle 100-200ma at the most. D5 isn't necessary unless you have some other unusual circuitry connected that is not shown.
 
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Dick Cappels

Active Member
And while at it, how about showing the connections to the motor and transformer so we don't have to use our imaginations? There could be a clue there too.
 

cbiblis

New Member
Couple of questions:
How large is the filter capacitor after the bridge rectifier?
What is the VA rating of the transformer? (VAC and AC amps)

You are drawing motor current through D5, a 1N4148, which can handle 100-200ma at the most.

There isn't a filter cap.
i have tried several transformers the smallest Va of the transformers is 12v 100ma. I would like to use my center tap transformer 6v/6v then my bridge rectifier. Output is 12.13v dc transformer is rated for 4.5 amps this circuit runs 100 ma but i will need extra power to run my lighting circuit 100ma and another 100 ma thermostat controller. I have a 300 ma transformer as well.
The funny thing is that my led lighting works on ac or dc, my thermo wants ac not dc and my motor control wants dc not ac. There picky little circuits.
 

cbiblis

New Member
the 12vinput-1 &-2 are the 120inputs the secondary output is 6v/6v. As for the motor they just connect to the motor from the motor connectors on the schematic. And another fix is the 6k8 resistor is actually a 6m8. Typo
 
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cbiblis

New Member
As for the motor pull, the motor and circuit max out at 102 ma so the n14148's shouldn't be an issue.
 
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cbiblis

New Member
actually here is the circuit fixed up sorry i got in a hurry. The only reason that the 1n4148's are in the circuit is that the design originally had a onboard transformer. I took it off but left the diodes.
 

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colin55

Well-Known Member
Are D1 and D2 around the correct way? Is the bridge around the correct way. What is 6M8? 47u is far too high, Pin 1 goes no-where. No values for R8 and R9. The chip is labelled IC2. 1N4148 diodes should not be used for 100mA. How many mistakes can a person produce on a such a simple circuit? You must take the prize. If the motor takes only 100mA, why use a FET?
 
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kchriste

New Member
Forum Supporter
There isn't a filter cap.
Well you need one. Especially if it is like the circuit in post #7. Try 1000uF or so for C7. As collin55 pointed out, there are multiple mistakes in the circuit. You need to redraw it.
 
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cbiblis

New Member
Are D1 and D2 around the correct way? Is the bridge around the correct way. What is 6M8? 47u is far too high, Pin 1 goes no-where. No values for R8 and R9. The chip is labelled IC2. 1N4148 diodes should not be used for 100mA. How many mistakes can a person produce on a such a simple circuit? You must take the prize. If the motor takes only 100mA, why use a FET?

This circuit was designed for me. it was designed for 12v i am trying to run it off of a transformer. 6M8 is a 6.8M resistor. Pin 1 is a grd and is not required by eagle to connect the program connects it for me. There is more to this circuit. thats why the labels are that way. This is a isolated circuit from the rest. i could take out the n14148's they were there when i had the circuit designed with and onboard transformer. The mosfet is in place in order to allow for upgrades. Plus i have about tem of these fets to use up.
So anyhow, If want to help please feel free if you just want to criticize I'm sure you can find spelling and grammatical errors as well, You could also search my user name and poke fun at my other posts as well. I mean what else is there to do on a Friday night for people like ourselves, except i've got kids to watch, How about you? :p
 

cbiblis

New Member

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audioguru

Well-Known Member
Most Helpful Member
The P-channel Mosfet is a follower. When its gate goes to ground then its source will be at about +10V, not 0V. Then the motor gets only 2V.
Use an N-channel Mosfet with its drain driving the motor wire to 0V.
 

cbiblis

New Member
ok, I swapped the cap from a 4.7uf to a 1000uf. Didn't make a differants, i also added a voltage regulator. all it did was drop the voltage down to 11.64vdc when it was reading 12.13vdc. So what else could i try?
 

audioguru

Well-Known Member
Most Helpful Member
A voltage regulator also needs a filtered input with at least 1000uF to ground. Its input voltage must be 2V higher than its output voltage.

Like I said in my previous post, the Mosfet is the wrong type and is connected wrong.
 

cbiblis

New Member
Actually, i got it working with the mosfet and the 4.7uf. I just turned the circuit on left it for a while when i came back it's working. I assume that ithe circuit needed time to charge the caps. I don't really know why it works but it does now. So thanks for ya'll input.:)
 

mneary

New Member
What kind of "NE555" are you using? 6.8M is an awfully high resistance to be putting into the RC circuit. Some types of "555" take more than 1 microamp on the trigger/threshold pins and 6.8M can barely supply this. I would change R11 to no higher than 2.2M and adjust R9, 10, and C6 accordingly.
I don't really know why it works but it does now.
Hopefully you're not going into production with a design that almost works.
 
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