How do I limit current

[kinarfi]

This circuit works well, it just draws too much current, and I was wondering if any one had a good way to limit the current to around 20 amps instead of the 70 amps(according to spice) I get now, which destroys my fets if I go too far. The circuit is shown with a current limit that I plan to try when my components get here, but is this the best way to do it. Would feed back work better? I have some Hall Effect devices that I can use, one is the ACS713 - 20A whicch would be maxed out, The other is a LEM HX 50-P/SP2 that has an offset voltage of 2.5 and an output of 0.0125 volts/ amp. If I use feed back that measures the current, where should I insert the feed back signal, U5 & U17? Any suggestion would be appreciated.
Thanks,
Jeff

 

[ronsimpson]

Change the value of R1. I don't know all about the circuit but R1 looks like a current limit circuit.

 

[ronv]

You have NFETs in the top. To fully turn them on you would need a voltage 10 volts or so higher than the 14 volts.
It kind of looks like an I bridge not an H bridge.

 

[kinarfi]

I Bridge, didn't know what that is, googled it, nothing, please explain I Bridge

This is what I plan to try when I get some supplies in (TIP35).
The PWM NFETs on top are sourced via the current limiting transistors
at the right that are limiting the current via the ground path.
Relays will switch the + side but are not PWM and are interlocked via
the N.C. contact of the 'other' relay. The transistor set up is doing a good job of limiting the current to near 20 amps in the Spice sims. The stock motor controller limits current to about 15 amps. What I really like about this design it that it has a lot smoother feel than the stock unit, but I need to limit the high end current, the stall specs on the motor, also not stock, are Operating v: 6v - 12v, Nominal v: 12v, Stall Torque: 343.27 oz-in
Stall Current: 133A, Kt: 2.58 oz-in/A, Kv: 443 rpm/V

 

[ronv]

Sorry, I was funning you over the I bridge. Didn't see the relays cause I don't have the model.
My old eyes aren't to good, but could you use the current sense to reset the 555 when the current goes over 20 amps.
I'll try to download some models tomorrow and have a look.

 

[Mosaic]

ronv post the models when u get em pls!