Need help designing circuit

Discussion in 'The Projects Forum' started by pnsn, Jul 15, 2011.

1. pnsn Thread Starter New Member

Jul 15, 2011
9
0
I have an electric cart and would like to use solenoids to control the speed. It has a 0 to 5 volt rheostat on the throttle pedal. I would like help on designing a small circuit that at 2 to 3 volts I could activate a solenoid, then at 4 or 5 volts cut the first solenoid and activate a second one.

Thanks
Rob

Last edited: Jul 15, 2011
2. #12 Expert

Nov 30, 2010
16,679
7,321
Without knowing the current through the rheostat or the size of the solenoids (voltage and current), I could design a perfectly useless circuit that does exactly what you described. More information is required.

3. pnsn Thread Starter New Member

Jul 15, 2011
9
0
This is a 12 volt dc system. I am going to use 12v solenoids too. I don't how many amps a solenoids pulls but I probably use a 2 or 3 amps fuse.

Thanks
Rob

4. pnsn Thread Starter New Member

Jul 15, 2011
9
0
I have an electric cart and would like to use solenoids to control the speed. It has a 0 to 5 volt rheostat on the throttle pedal. I would like help on designing a small circuit that at 2 to 3 volts I could activate a solenoid, then at 4 or 5 volts cut the first solenoid and activate a second one.

This is a 12 volt dc system. I am going to use 12v solenoids too. I don't how many amps a solenoids pulls but I probably use a 2 amp fuse.

Thanks
Rob

Jul 7, 2009
1,585
141
It's not clear what you want to do. How are solenoids going to control the speed? A solenoid is typically a chunk of ferromagnetic material inside a cylindrically-wound coil. However, in automotive usage, the term is corrupted to mean a SPST relay that can handle automotive starting currents. Is this what you mean?

Also, what is the problem with using the existing speed control?

Conceptually, the basic task can be done with some comparators and digital logic. However, when you're talking 12 V motors, "solenoids", etc., there are often nasty voltage spikes because of inductive kickback, so the design has to proceed a bit more cautiously. Fortunately, there are experts on this board who can help (but I'm not one of them ).

6. castley Member

Jul 17, 2011
31
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need to know more about the solenoids, such as coil resistance work to be done by the solenoid

7. pnsn Thread Starter New Member

Jul 15, 2011
9
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Yes the solenoids are going to connected to the motor. The first solenoid will provide 24v to the motor, the second will provide 48v to it.

Thanks
Rob

8. #12 Expert

Nov 30, 2010
16,679
7,321
Repeating post number 3. You did not say what voltage or current the solenoids use.

9. Kermit2 AAC Fanatic!

Feb 5, 2010
3,849
965
putting together all of your descriptions.

You have a 12 volt system
You have a 0-5 volt rheostat
You want to trigger at 2-3 volts
You want another trigger at 4-5 volts
You want solenoids to provide 24 volts
you want another solenoid to provide 48 volts

???

Figure out what you want and what you have, and you will get better help

10. pnsn Thread Starter New Member

Jul 15, 2011
9
0
Yes, that is correct. These are old starter solenoids that use to set on the firewall and turned on the starter. They can't use more than 1 amps to activate the solenoid and use 12 volts to do that.

Thanks
Rob

11. simo_x Member

Dec 23, 2010
200
6
WTF... Who are you writing to?

12. JingleJoe Member

Jul 23, 2011
185
10

the buttons are very close together and look almost exactly alike so it;s an easy mistake to make

Apr 5, 2008
15,799
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14. pnsn Thread Starter New Member

Jul 15, 2011
9
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Yes, can you merge my threads

Thanks
Rob

Apr 5, 2008
15,799
2,386
Hello,

I have merged the three threads.
The posts will show in order of posting.

Bertus

16. pnsn Thread Starter New Member

Jul 15, 2011
9
0
I have had some questions, but no one has responded on how to make this circuit. Do you know how?

Thanks
Rob

17. SgtWookie Expert

Jul 17, 2007
22,183
1,728
OK, you have several starter solenoids, and a system that is operated by 12v.

Do you have multiple batteries that you want to connect in series, depending on which solenoid is engaged?

That is not how it's usually done - as the battery lowest in the series circuit will wind up getting discharged more quickly than the rest of the batteries; because as long as the cart is moving, that battery will be in use.

Did you know that starter solenoids are not meant for continuous service? You can engage them for perhaps a couple of minutes, but they are just designed to be used for supplying heavy current to start an engine, not as a continuously engaged relay.

18. pnsn Thread Starter New Member

Jul 15, 2011
9
0
These solenoids are designed for continuous use. Anyway, how do I make the circuit to control these?

Thanks
Rob

19. SgtWookie Expert

Jul 17, 2007
22,183
1,728
Do you have a part number and manufacturer for the solenoids?
Or, can you simply verify if the coil is independent (infinite Ohms) from the solenoid contacts using a multimeter?

20. pnsn Thread Starter New Member

Jul 15, 2011
9
0
Forget the solenoids, I will use small relays to trigger the solenoids. These relays will only draw about 0.1 an amp.

Is this circuit hard to draw out?

Thanks
Rob