switching high inductance loads

[NavMicroSystems]

Could you post your schematic?

switching high inductive loads is always a challenge.

Some things that may help:

- Check for Ground Loops
- reverse diodes accross all coils.
- RC filters across the relays contacts
- RC Filters at the PICs and Drivers I/O Pins
- Many large Ground Planes
- Relays as far as possible away from the PIC
- opto-isolators between MCU and drivers
- If switching AC, toggle the relays at zero crossing !

etc...

[kitcat]

Here is a rough schematic. The relevent parts anyway. Sorry it is so bad!

The problem occurs with just one tiny solenoid connected and without the uln2803 plugged in. So just sending a pulse to one test solenoid causes the problem. Are you saying that I should remove the relay from the board and just send the feed back?
Thanks

[kitcat]

Hmmmnn having trouble uploading !

[kitcat]

Another try.

[Dave]

kitcat, I assume from the schematic you are using one of the Allegro driver chips but I don't see pin 10 connected directly to the solenoid + supply. The reverse diode in series with this pin makes any connections to it useless.
I have used quite a few of the Allegro (formerly Sprague) drivers and I have never experenced any problems with them reseting any processors I have connected to them. One thing to keep in mind when using these multiple sinking or sourcing drivers is the current return path in the case of sinking drivers, and the supply path in the case of sourcing drivers should be as direct to the current supply as possible. Therefore in your application the pin 9 of your selected driver should have a seprate high current path to the current source "return" and the pin 10 should be going to the the closest point of the "loads" current source.
Dave Purola,

[NavMicroSystems]

kitcat,

First of all:
As Dave has already mentioned: Pin 10 of the 2803 MUST be connected to the positive supply of the solenoids.
(+12V in your case)

BTW
according to the schematic the Drivers on Pins 11 & 12 of the 2803 are not used.
If so, you could drive the relay off one of those pins and get rid of the transistor, diode and resistor.

Your schematic is not really clear,
what are the relay pins connected to?
(they some appear to be unconnected in your schematic)

Could you complete the schematic before we continue guessing?

[Luciano]

Hi,

See page 6 of this PDF (Fig.3).
http://www.pololu.com/products/misc/0024/sn754410.pdf

(fig 3). If you set Control A to "1" the current will flow
in one direction in the motor winding (or your solenoid) and if you
set Control A to "0" the current will flow in the opposite direction
in the motor winding (or your solenoid).

Same for Control B (Your second solenoid).

External diodes are mandatory!

* * *

With two IC 7406 (inverting buffer), three IC SN754410 and 24 diodes you
can drive your six solenoids.

(You can find similar driver ICs with built-in diodes).


Luciano

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Edit:
One IC with built-in output clamp diodes for inductive transient suppression is the L293D.
The "D" at the end is for Diodes. The model L293 is without diodes.

See page 8 of this PDF.

(Texas Instruments Datasheet SLRS008C − SEPTEMBER 1986 − REVISED NOVEMBER 2004)
L293, L293D QUADRUPLE HALF-H DRIVERS

http://focus.ti.com/lit/ds/symlink/l293d.pdf

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