simonr Posted September 17, 2008 Share Posted September 17, 2008 For those of you who don't know what a Peak&Hold driver is - Solenoids, including injectors, need a good 'kick' of current to actuate but much less (typically half) to hold. Generally if you hold them at full current they over-heat. I have built a solenoid free-spool for EP9 & Tds winches which uses a solenoid (surprisingly! ). It works pretty well - but if you hold the freespool disengaged (it uses a spring to return to being locked) for too long - it gets VERY hot! I need to find a simple, cheap, single channel device which will provide the Peak & Hold function without the person operating the switch ever being aware of it. There are several chips which provide this - but I'd rather not have to worry about assembling and boxing circuit boards if something already exists. I figure there might be such a thing available as an injector driver for throttle body (single) injectors. I believe KAM diff-locks use something similar - which might be an option - but probably too expensive. (Is anyone from KAM on 'ere?) Any ideas would be much appreciated! Si Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted September 17, 2008 Share Posted September 17, 2008 Since you've already found the chip that does PWM, going back to a rather basic solution what about this? Did that too quickly, the solenoid is at the bottom, the resistor is parallel with the cap.) The cap charging up would give an initial current kick, then the resistor would allow a constant current to flow, and discharge the cap when power was removed. Quote Link to comment Share on other sites More sharing options...
simonr Posted September 18, 2008 Author Share Posted September 18, 2008 Thanks John. Trouble is the size of Cap required to deliver enough of a kick. I reckon on 10A for 200ms minimum It therefore needs to deliver about 2 C of charge. Q=IT It's running at 12v so the capacitance is given by Q=CV so C = 2/12F or 166,000uF Quite a chunky Electrolytic! Now, that calculation is a bit simplistic as the current will trail off over the course of the cap charging - so you may only get enough of a 'kick' for maybe 1/3 of the full charge time - so you may in fact be up into a 0.5F capacitor! In practice, you would use a transistor to amplify the current - with a single transistor with a gain of 100 you could reduce the capacitor to 5,000uF which is far more manageable. Si Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted September 18, 2008 Share Posted September 18, 2008 By the time you've used a cap & transistor you may as well use that PWM driver and have a really solid solution, I think whatever you use you'll end up potting it into a box. Unless you just use a constantly rated solenoid, like KAM do. From a more mechanical angle, what about a switch that is actuated by the solenoid opening that switches an inline resistor into the circuit? Wouldn't need to be big, perhaps a sealed reed switch. Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted September 18, 2008 Share Posted September 18, 2008 Now, that calculation is a bit simplistic Oh you think so do you ? Nige Quote Link to comment Share on other sites More sharing options...
andyb Posted September 18, 2008 Share Posted September 18, 2008 I was just thinking that it was time for a "bunny with a pancake on it's head" Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted September 18, 2008 Share Posted September 18, 2008 Will this do? Quote Link to comment Share on other sites More sharing options...
Off Road Toad Posted September 18, 2008 Share Posted September 18, 2008 For those of you who don't know what a Peak&Hold driver is - Solenoids, including injectors, need a good 'kick' of current to actuate but much less (typically half) to hold. Generally if you hold them at full current they over-heat.I have built a solenoid free-spool for EP9 & Tds winches which uses a solenoid (surprisingly! ). It works pretty well - but if you hold the freespool disengaged (it uses a spring to return to being locked) for too long - it gets VERY hot! I need to find a simple, cheap, single channel device which will provide the Peak & Hold function without the person operating the switch ever being aware of it. There are several chips which provide this - but I'd rather not have to worry about assembling and boxing circuit boards if something already exists. I figure there might be such a thing available as an injector driver for throttle body (single) injectors. I believe KAM diff-locks use something similar - which might be an option - but probably too expensive. (Is anyone from KAM on 'ere?) Any ideas would be much appreciated! Si Hi Simon, we might be able to help you out. i believe you need a coil commander which we can do.please give us a call on 01483 419779 and ask for Chris or Steve. or an email: steve@kamdiffs.com regards, Steve Quote Link to comment Share on other sites More sharing options...
steve_d Posted September 18, 2008 Share Posted September 18, 2008 Hi Simon, we might be able to help you out. i believe you need a coil commander which we can do.please give us a call on 01483 419779 and ask for Chris or Steve. or an email: steve@kamdiffs.com regards, Steve Can you post more info or a link please. You have legitimately answered someone's question so cannot (in my opinion) be accused of advertising on the forum. Steve Quote Link to comment Share on other sites More sharing options...
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