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automotive circuit / module design needed
2

automotive circuit / module design needed

automotive circuit / module design needed

(OP)
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
 

RE: automotive circuit / module design needed

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

RE: automotive circuit / module design needed

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

Keith Cress
kcress - http://www.flaminsystems.com

RE: automotive circuit / module design needed

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.
 

RE: automotive circuit / module design needed

(OP)
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
 

RE: automotive circuit / module design needed

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

Cheers

RE: automotive circuit / module design needed

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 !)

 

RE: automotive circuit / module design needed

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

thanks Skogsgurra!!

RE: automotive circuit / module design needed

Nice. And fast feed-back, too!

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: automotive circuit / module design needed

(OP)
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

RE: automotive circuit / module design needed

(OP)
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?

RE: automotive circuit / module design needed

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

RE: automotive circuit / module design needed

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

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

RE: automotive circuit / module design needed

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.

 

RE: automotive circuit / module design needed

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).
 

RE: automotive circuit / module design needed

(OP)
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!

RE: automotive circuit / module design needed

(OP)
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%252bk0S5zvCaqPu98g0%2f%2fcw%3d%3d

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!

RE: automotive circuit / module design needed

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!

RE: automotive circuit / module design needed

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.

RE: automotive circuit / module design needed

As several have already said; you have to do some experimenting to find out what works best.

LiteYear The lamp does NOT behave like a resistor. It has a low resistance when cold and resistance increases five to ten times when heated. That is why you get a decent torque from the motor and that is also why the motor doesn't burn out when stalled. Forget the linear calculation, it doesn't hold.

Also, a PTC increases resistance and "self-holds" so you need an alternate path to reverse the motor, as OperaHouse says. You do not need that with an incandescent lamp.

And, finally. The lamp allows a certain "holding current" so that there is always some torque left to keep things closed (or opened) at end-of-travel.

I think this circuit holds a world record in simplicity and functionality.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: automotive circuit / module design needed

(OP)
http://www.grote.com/product.php?product_number=45822&x=0&y=0

thats the bulb currently in the circuit, its working great, but like i said im trying to get it all down in size to mount all the components in a poly enclosure of roughly 2"x1.5"x1.5".  so a small snap in incandesant bulb would be optimal, got a dpdt 8 pin relay and snap mount relay socket to scale down the rest.  right now im running 2 seperate relays.

ill track down a 100ma bulb and try it before i buy any quantity of the before mentioned ones.

thanks everyone, and like the last post states, this is so simple its not funny. love it.

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

RE: automotive circuit / module design needed

Quote (Skogsgurra):

LiteYear The lamp does NOT behave like a resistor.

Holy moly, you're quite right. The humble lamp really does provide non-linear resistance of 5-10 fold. That's awesome! Learn something every day.

So my post is mostly rubbish - only the fact that current will be capped at about 100mA is correct.

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