You could try a 1-2 Farad car audio capacitor, basically it's there to try to reduce the voltage sag when a bass note hits etc... would work the same for your application, it would be best to hook it up near the offending device. If there is more than one offender then mount it close to the output of the chennic... this would work well for an always on dc/dc converter, however if the cap was allowed to drain when you turn off the car it would be an insane load on the chennic and probably blow it up. It basically needs a pre-charge sequence just like the controller. Otherwise a small battery, since your a lithium user now, 4 series 10ah headways would be small and provide enough power.
minimizing dc-dc voltage sag?
1 - 20 of 20 Posts
I like the idea of a capacitor since it would last 'forever'... but I am a little bummed the Chennic dc-dc wouldn't have something like this built in already. I guess that is what makes it cheap. 
So, tell me a little more about what I need to do to manage the 'pre-charge' or initial inrush on the rare occasions I power down the system. The dc-dc is normally 'always on' as this is my daily driver, but I do occasionally power down when working on something.
And, would I get something like this for a decent price at a local Radio Shack, or a car stereo place, or somewhere else?
So, tell me a little more about what I need to do to manage the 'pre-charge' or initial inrush on the rare occasions I power down the system. The dc-dc is normally 'always on' as this is my daily driver, but I do occasionally power down when working on something.
And, would I get something like this for a decent price at a local Radio Shack, or a car stereo place, or somewhere else?
Basically for precharge you simply need to apply 12v through a current limiting resistor (the cap should come with the resistor for initial charging).I like the idea of a capacitor since it would last 'forever'... but I am a little bummed the Chennic dc-dc wouldn't have something like this built in already. I guess that is what makes it cheap.
So, tell me a little more about what I need to do to manage the 'pre-charge' or initial inrush on the rare occasions I power down the system. The dc-dc is normally 'always on' as this is my daily driver, but I do occasionally power down when working on something.
And, would I get something like this for a decent price at a local Radio Shack, or a car stereo place, or somewhere else?
Then you connect the power directly. It's a very simple process, just something you would need to remember to do that's all. With a couple of relays and some sort of delay you could impliment an "automatic" setup much like the precharge control in motor controllers.
You can get these capacitors all over the place, here's what a 2 second search on amazon turned up:
http://www.amazon.com/Raptor-C1-0FM...TJBO/ref=sr_1_1?ie=UTF8&qid=1299083186&sr=8-1
It has a built in volt meter, which you may or may not like, there are more basic ones without the meter.
I think the capacitor approach sounds great provided the power needs aren't too much. Just keep in mind that a 1-2 farad cap may look huge but doesn't hold that much juice compared to batteries. Back in HS I was running a couple 12s at 400 watts and the headlights would flash every time the bass hit. Adding a 1F cap took care of that. ebay was by far the cheapest source at the time. IIRC 1F was < $30.I like the idea of a capacitor since it would last 'forever'... but I am a little bummed the Chennic dc-dc wouldn't have something like this built in already. I guess that is what makes it cheap.
For the precharge, since you rarely power down just use a light bulb or a switched resistor. You don't need a complex timer and relay system for something you're rarely needing. However, you should fuse it in case you forget, and depending on how forgetful you are, the relay setup as rwaudio mentioned could help out.
I'm quite amazed they don't have this built in, but when you get an audio stiffening cap it comes with a light bulb or resistor to precharge it.
A few farads of capacitor behaves a lot like a very small capacity battery with very low internal resistance (that lasts a lot longer and doesn't care about being run dead.) If the DC to DC is ever off, even for 10 minutes, it is almost certain the cap will discharge with just the small parasitic loads in a car. When the DC to DC comes back on it will "see" the discharged cap as a short circuit until it charges up (a much more painful one than my headlights or your vacuum pump.) I don't know if the inexpensive Kelly and Chennic DC to DC converters can handle a few farads of capacitive load, it is a lot more than generally present in devices. It is a lot more than is inside your controller!
1 - 20 of 20 Posts
