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limiting amperage, follow up

J

John Whittaker

Jan 1, 1970
0
Ok, more meat for the bones. The device is an electronic locker for the
rear end of my Jeep. The locker is engaged by an electromagnetic, and the
more current you allow it, the more it locks up. I would like to be able to
have a three position switch that would allow 1. no current, 2. 12 volts,
but limit the amperage to only 1 amp, and 3. 12 volts, and the total draw,
where it would be around 7 amps. This would allow me to have a limited slip
in one position, a stronger limited slip in the second, and the differential
completely locked up in the third and final. (even with no current, the
differential still has limited slip capability) Hope that helps.

John Whittaker
 
J

Jamie

Jan 1, 1970
0
John said:
Ok, more meat for the bones. The device is an electronic locker for the
rear end of my Jeep. The locker is engaged by an electromagnetic, and the
more current you allow it, the more it locks up. I would like to be able to
have a three position switch that would allow 1. no current, 2. 12 volts,
but limit the amperage to only 1 amp, and 3. 12 volts, and the total draw,
where it would be around 7 amps. This would allow me to have a limited slip
in one position, a stronger limited slip in the second, and the differential
completely locked up in the third and final. (even with no current, the
differential still has limited slip capability) Hope that helps.

John Whittaker
They make electric trailer brake controls for that..
you can get them at hardware stores where they
sell boat, camper etc accessories.

basically a Rheostat of sorts.
 
E

ehsjr

Jan 1, 1970
0
John said:
Ok, more meat for the bones. The device is an electronic locker for the
rear end of my Jeep. The locker is engaged by an electromagnetic, and the
more current you allow it, the more it locks up. I would like to be able to
have a three position switch that would allow 1. no current, 2. 12 volts,
but limit the amperage to only 1 amp, and 3. 12 volts, and the total draw,
where it would be around 7 amps. This would allow me to have a limited slip
in one position, a stronger limited slip in the second, and the differential
completely locked up in the third and final. (even with no current, the
differential still has limited slip capability) Hope that helps.

John Whittaker

This will do it:

+12---+---o> o1
|
| o2------------+---[Ry1]---+
o | |
| o3---+--->|---+----|<-----+
Ry-1 |<| | |
N/O | +--------+---[Ry2]---+--- Gnd
| | |
| |<| RY2 +-----|<----+
| | | N/O
+-------o o------------------------+
| |
[.5R] |
| ----- |
+------+----Vin|LM317|Vout---+ |
| | ----- | |
| | Adj [1.2R] |
[TVS] [.1uF] | | |
| | +----------+-----+--- To locker
| |
Gnd ----+------+------------------------------- To Locker

The LM317 will need to be on a good heatsink. The Ry1 N/O
contact is the on/off switch. The RY2 N/O contact selects
whether the circuit provides 1 amp or full current. With
Ry1 energized, the circuit is on, and with Ry2 energized,
full current will be available from the circuit. With Ry1
energized and Ry2 not energized, 1 amp will be available
from the circuit.

Use automotive relays - their contacts are rated at 20 amps
or more. The 1.2 ohm resistor needs to be at least 2 watts.
The diodes can be 1N400x. The TVS can be a 1.5KE24CA and
the .5 ohm resistor can be two 1 ohm 10 watt resistors in
paralell. Those parts are used to give the LM317 some
protection from the jeep's electrical system which is likely
to produce some high voltage spikes.

Ed
 
J

jasen

Jan 1, 1970
0
Ok, more meat for the bones. The device is an electronic locker for the
rear end of my Jeep.
differential locker.

The locker is engaged by an electromagnetic, and the
more current you allow it, the more it locks up. I would like to be able to
have a three position switch that would allow 1. no current, 2. 12 volts,
but limit the amperage to only 1 amp, and 3. 12 volts, and the total draw,
where it would be around 7 amps.

put a 15W brake lamp in series with the line feeding it, that'll give reduce
the current to close enough to 1A. You could use a 10W (or larger) 10ohm
resistor - it'll get hot (as does the lamp) so mount it somewhere where
air circulates.
This would allow me to have a limited slip
in one position, a stronger limited slip in the second, and the differential
completely locked up in the third and final. (even with no current, the
differential still has limited slip capability) Hope that helps.

could work, could break something, have you checked that out?
 
R

Ross Herbert

Jan 1, 1970
0
Ok, more meat for the bones. The device is an electronic locker for the
rear end of my Jeep. The locker is engaged by an electromagnetic, and the
more current you allow it, the more it locks up. I would like to be able to
have a three position switch that would allow 1. no current, 2. 12 volts,
but limit the amperage to only 1 amp, and 3. 12 volts, and the total draw,
where it would be around 7 amps. This would allow me to have a limited slip
in one position, a stronger limited slip in the second, and the differential
completely locked up in the third and final. (even with no current, the
differential still has limited slip capability) Hope that helps.

John Whittaker

Have you thought about the legal ramifications or implications of
fitting a simple DIY electromagnetic controller to your vehicle? It
may even be illegal to do so if it doesn't meet certain design
criteria. I don't know myself but I thought it might be worth a
mention.

Why not investigate controllers already designed and approved for such
applications? eg.
http://www.gkndriveline.com/gkn-driveline/jsp_en/solutions/tmd/emcd.jsp
 
J

jasen

Jan 1, 1970
0
This will do it:
+12---+---o> o1
|
| o2------------+---[Ry1]---+
o | |
| o3---+--->|---+----|<-----+
Ry-1 |<| | |
N/O | +--------+---[Ry2]---+--- Gnd
| | |
| |<| RY2 +-----|<----+
| | | N/O
+-------o o------------------------+
| |
[.5R] |
| ----- |
+------+----Vin|LM317|Vout---+ |
| | ----- | |
| | Adj [1.2R] |
[TVS] [.1uF] | | |
| | +----------+-----+--- To locker
| |
Gnd ----+------+------------------------------- To Locker

The LM317 will need to be on a good heatsink.

What's the TVS for?

I can see it destroying the LM317 if a surge hits with
both relays energised.

the locker mechanism is likely a large electromagnet.

when RY2 opens you've got more problems. the inductance of the electromagnet
will fly back and exceed the voltage rating of the 317.

the locker mechanism is likely a large electromagnet.
but with a DC supply it's behavior is basically that of a resistor,

7A from 13.5V is pretty close to 2 ohms, another 11 in series will get him
close to 1A and avoids delicate semiconductors and the need for a heatsink.

ventilation is still needed.

Bye.
Jasen
 
E

ehsjr

Jan 1, 1970
0
jasen said:
John said:
Ok, more meat for the bones. The device is an electronic locker for the
rear end of my Jeep. The locker is engaged by an electromagnetic, and the
more current you allow it, the more it locks up. I would like to be able to
have a three position switch that would allow 1. no current, 2. 12 volts,
but limit the amperage to only 1 amp, and 3. 12 volts, and the total draw,
where it would be around 7 amps. This would allow me to have a limited slip
in one position, a stronger limited slip in the second, and the differential
completely locked up in the third and final. (even with no current, the
differential still has limited slip capability) Hope that helps.

John Whittaker


This will do it:

+12---+---o> o1
|
| o2------------+---[Ry1]---+
o | |
| o3---+--->|---+----|<-----+
Ry-1 |<| | |
N/O | +--------+---[Ry2]---+--- Gnd
| | |
| |<| RY2 +-----|<----+
| | | N/O
+-------o o------------------------+
| |
[.5R] |
| ----- |
+------+----Vin|LM317|Vout---+ |
| | ----- | |
| | Adj [1.2R] |
[TVS] [.1uF] | | |
| | +----------+-----+--- To locker
| |
Gnd ----+------+------------------------------- To Locker

The LM317 will need to be on a good heatsink.


What's the TVS for?

That was described in the part you snipped.
I can see it destroying the LM317 if a surge hits with
both relays energised.

Sounds valid. Would you like to add a diode?
the locker mechanism is likely a large electromagnet.

when RY2 opens you've got more problems. the inductance of the electromagnet
will fly back and exceed the voltage rating of the 317.

Sounds valid. Would you like to add a diode?
the locker mechanism is likely a large electromagnet.
but with a DC supply it's behavior is basically that of a resistor,

7A from 13.5V is pretty close to 2 ohms, another 11 in series will get him
close to 1A and avoids delicate semiconductors and the need for a heatsink.

So, keep the relays and replace the electronics
(everything below RY2 N/O on the diagram) with
11 ohms at say 20 watts?

Ed
 
J

jasen

Jan 1, 1970
0
This will do it:
+12---+---o> o1
|
| o2------------+---[Ry1]---+
o | |
| o3---+--->|---+----|<-----+
Ry-1 |<| | |
N/O | +--------+---[Ry2]---+--- Gnd
| | |
| |<| RY2 +-----|<----+
| | | N/O
+-------o o------------------------+
| |
[.5R] |
| ----- |
+------+----Vin|LM317|Vout---+ |
| | ----- | |
| | Adj [1.2R] |
[TVS] [.1uF] | | |
| | +----------+-----+--- To locker
| |
Gnd ----+------+------------------------------- To Locker

The LM317 will need to be on a good heatsink.
What's the TVS for?

That was described in the part you snipped.

The question was somewhat rhetorical.
Sounds valid. Would you like to add a diode?

(diode "backwards" between vout and vin)
that'd do it, losing the cap and the .5R and connecting the tvs
between Vin and adj could work too.
Sounds valid. Would you like to add a diode?

(diode from ground to adj) that'd fix that one.
My mod above might do it too.


I dont think a great deal of precision is needed.
So, keep the relays and replace the electronics
(everything below RY2 N/O on the diagram) with
11 ohms at say 20 watts?

I'd just look for a suitable switch if the wiring was
practical, a "0-I-II" three position rocker switch rated
at 10A (and the resistor) would probably do.

Bye.
Jasen
 
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