automotive circuit / module design needed 2

[gerryfoster]

Hello all.

I'm new to this forum and would like to say hello!

I'm a custom shop owner and am prototyping a system and need some help.

ill describe to the best of my knowledge what im trying to do and what I'm looking for....

I am wanting to control a simple reversible DC motor roughly 1 amp draw.

I need to run this motor in both directions (reverse polarity)

here's where it gets over my head....

I need a current sensing setup to stop motor when it reaches its stop.

also i need a different type of input to control this motor, i want it to work exactly like a power antenna does? apply 12 volts to turn the motor and have it stop at it's limit, stay in that position until the 12 volts is removed, at that time turn the motor in the opposite direction until it again stops at it limit.

the use of this set up it to automatically control an electric exhaust cut out, which i have plans to control with another system which outputs the 12 volts on/off as mentioned.

i have a lot of experience in automotive electrical but not in the designing of circuity.

any help would be greatly helpful.

thanks Gerry

 

[Skogsgurra]

If I got this right:
Supply voltage is always pesent.
Control voltage is 12 V and can be on or off.
When ctrl is 12 V, motor moves out until current gets excessive. It then stops.
When ctrl is 0 V, motor moves in until current gets excessiv. It then stops.

This would be a no-brainer if it weren't for the current sense and need to latch the sensed current to prevent further motion. Using a small micro and a state machine is what any EE would do, but I feel that you would like to use relays all the way. It can be done and all you need is a few more relays. But I don't like that approach.

You can also use a primitive method where you limit current with a series resistor and contorl OUT/IN with the control voltage. That will drain your battery if left in-circuit with engine off. So, you need to connect the system so it is disconnected when engine is off. Doing this, you only need two relays (no-brainer) and a resistor around 10 ohms, 10 W or more. You could probaby use a 6 W lamp instead of the resistor. You may need to use a larger lamp, but the principle holds.

The nice thing with the lamp is that it is low ohm until current rises. It then goes high ohm to reduce current further.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[itsmoked]

Or do you have switches available to stop the motor at the two final positions?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[benta]

This is an absolute no-brainer.
The current-sensing stop is built into every window hoist, and cars today practically all have electrical windows. Go buy a controller for a window hoist.

Cheers,

Benta.

 

[gerryfoster]

I have tried to brands of one touch window modules.....they don't seem to recognize the low amperage I'm using......directed 530T and autoloc WC1000
I don't have switches to sense stops.

Sko u have the theory perfect. How would you wire the relays/light bulb idea u speak of?

Thanks

 

[Skogsgurra]

Like attached. (Note "AN" means "AND")

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[gerryfoster]

Great, ill give this a shot and let ya know.

Cheers

 

[zzzjim]

Next level of lo tech tweaking to G.Englund's Circuit ,

add a relay with its N/C contacts in series with the bulb ,and coil driven by the voltage across the bulb and its own contacts . It will self isolate and un-latch when the power is off long enough !

( Hope this verbal circuit is ok , Xmas !)

 

[gerryfoster]

works GREAT! thanks ill keep u posted when i get it installed and functioning.

thanks Skogsgurra!!

 

[Skogsgurra]

Nice. And fast feed-back, too!

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[gerryfoster]

Hey Skogsrurra

im a bit concerned with the circuit when the motor stops and the bulb illuminates. the motor is still a bit loaded (trying to move) at this point......my question is will this hurt the motor long term? or can i use a smaller wattage bulb to lessen this? im using a 194 waffle bulb now which is roughly 3 watts from what i looked up.

it works exactly as you said it does and i thank you for that, just want to know what you think about this....

thanks

 

[gerryfoster]

zzzjim, i missed your post in my excitement that its working....

could you please describe your addition a bit better?

im using 5 pin relays

#30 common
#87 no
#87a nc
#85 coil
#86 coil

could you give me an idea what wires to put on what pins?

 

[Skogsgurra]

No probs, Gerry. This application is quite common and the only concern would be the local heating of the motor winding and the commutator bars. As long as your armature current is below around half rated current, this heating is of no concern.
Your 3 W bulb reduces current to around .25 A - which is well below the 1 A current you mentioned. And probably way below rated current. "Just do it!"
No need to complicate things.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[ScottyUK]

Following up Benta's idea, just change the current sense resistor to a higher value to make it more sensitive.


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If we learn from our mistakes I'm getting a great education!

 

[OperaHouse]

Tom answer your question, two of those relays are needed. The NC of one relay would connect to the NO of the other with coils in parallel. OR buy a relay with two sets of contacts. Asking that question indicates any more complex choice is out of the question.

 

[VEBill]

A center-off, spring-return DPDT toggle switch could be the basis of a slightly better solution. But might still need the light bulb (installed next to the switch as user feedback).

 

[gerryfoster]

sko's setup is working great as is......just awiting installing in its application and get it working in real life, as for bench testing is great!

Crappy Car Customs.......we make you CRAP custom!

 

[gerryfoster]

SKOGSGURRA.....

can you tell me if a 100ma light bulb will work in this circuit?

this is the one i was thinking.

http://ca.mouser.com/ProductDetail/Chicago-Miniature/1090A5-12V/?qs=N8%2bk0S5zvCaqPu98g0//cw==

i have this circuit working on the vehicle now and its waorking great, just trying to get all the components to scale down the size of the whole package. thanks for all the help. Gerry

Crappy Car Customs.......we make you CRAP custom!

 

[LiteYear]

While you're waiting for Skogsgurra you could think of it like this:

A 100mA lamp is effectively a 120Ohm resistor. That will restrict the current in the circuit to at most 100mA for a stalled motor - quite small and certainly no strain on the motor.

During motor operation however, the motor will only have available the voltage and current as described by the circuit equation: V=12-120I. For example, 3V @ 75mA, 6V @ 50mA or 9V @ 25mA. The greatest motor power you can hope for is 6V @ 50mA = 0.3W, but only if your motor's voltage-current curve intersects this point. Given the motor was a 1A motor (and therefore had a nominal power rating of 12W), it might not suit this power range very well.

If your motor had plenty of power using the 3W bulb then you might get away with the 100mA lamp. If not, the 100mA lamp might make it underpowered. Hard to tell, might have to try it!

 

[OperaHouse]

If you really want to scale it down I would use PTC thermal fuses. These are only about .1 ohm resistance but would be a couple gundred ohm when they heat up. You would need to use TWO with a 1A diode in series with each one to accomodate current in both directions, Without using tow, when the PTC heated up you couldn't reverse direction. PTC fuses are actually found in better quality C motors to prevent burnout in the event of a stall. PTC fuses will give a much better operation over time with less heat.