โAug-27-2015 06:21 PM
โAug-29-2015 02:48 PM
โAug-29-2015 02:30 PM
โAug-29-2015 12:55 PM
โAug-29-2015 10:18 AM
โAug-29-2015 10:10 AM
MrWizard wrote:
I have to ask (except for the lack of a face plate mounting)
How is this any different than a work bench power supply, with vernier knobs for voltage control, mounted in the face plate and "cabled" to the circuit board
โAug-29-2015 10:07 AM
โAug-29-2015 10:04 AM
Salvo wrote:
LOL, I don't give sh*t what happens to you're PS.
It appears to me you two think this is a pissing match. However, I just gave my professional opinion. Do with it what you want. Not going to waist my time with non appreciative, cocky people.NinerBikes wrote:
...if you are really curious and can't wait, get a MegaWatt, mod it yourself and find out for us.... otherwise some patience is in order, and that's if SCVjeff doesn't have a lot of better things to do with what limited spare time he has. He did this for me as a big favor, I don't want my posting up of the favor he gave me becoming a pizzing contest between a couple of EE guys, so if you have questions, PM each other, or not, if out of respect for each other.
โAug-29-2015 09:59 AM
MEXICOWANDERER wrote:
Using the OE pot at max 1K as a pull down resistor, this means LEAVING the oe pot in place, an open circuit to the remote pot becomes a moot point. The control circuit will default to the original pot setting. I am more concerned with inductance than I am with ESD which should NOT be a concern if the circuit is fully shielded, grounded and sealed.
Don't know how much experience you have with lightning but I have seen s frightening amount of voltage induced into isolated circuits. Long lengths of wire, coils, transformers, you name it. The E level is not harmful to humans indeed I doubt whether it could be felt at all, but to an ultra-sensitive circuit the risk isn't worth ignoring.
UN-flat on a 20mv scale is rather loose terminology. However now I am musing the validity of screening the two Megas using a basic Faraday shield. Nicaragua is a hell of a bad place to discover circuit design weaknesses or vulnerabilities.
Sorry Niner, I was using euphemisms to describe tolerating or weighing an unknown risk versus an unknown hazard. For a general idea of one electronic phenomenon, Google ELECTRONIC TANK CIRCUIT, read and understand what it means.
One little, two little, three little millivolts. Four little, five little, six little millivolts...
โAug-29-2015 09:58 AM
NinerBikes wrote:
...if you are really curious and can't wait, get a MegaWatt, mod it yourself and find out for us.... otherwise some patience is in order, and that's if SCVjeff doesn't have a lot of better things to do with what limited spare time he has. He did this for me as a big favor, I don't want my posting up of the favor he gave me becoming a pizzing contest between a couple of EE guys, so if you have questions, PM each other, or not, if out of respect for each other.
โAug-29-2015 09:34 AM
โAug-29-2015 09:33 AM
Salvo wrote:
Here I though I was done with this topic.
The worst case scenario for any PS is turning it into an oscillator. I'm not saying that's the case there, but after the mod, the PS should be tested for oscillator tendencies. After all, the cable is connected to the most sensitive area within the PS.
You can minimize noise injection by limiting the cable length to <1.5" and using a bracket to mount the pot. Now there's no human body contact with the cable.
If there is oscillation, it's most likely not going to affect the battery as it is a huge capacitor. Perhaps you now have a "pulse charger". The oscillations may however exceed the limits of some of the components within the PS. That would be the primary concern.
Before doing anything further, I would test the output (unloaded) with a scope (ac setting, 200 mV/div). If the trace is flat, even when grabbing the cable or pot, then no further work in required.
Another potential problem is if one of the pot cables breaks off. What happens to the output voltage? Does it go to zero volts or does it go sky high? Or is it limited to a safe value? If it goes high you'll hear the output caps go pop. The PS reliability definitely decreased with the added pot. Mounting the pot to a bracket will help a lot.
โAug-29-2015 09:07 AM
โAug-28-2015 11:39 PM
โAug-28-2015 10:04 PM
MEXICOWANDERER wrote:Salvo wrote:
I wouldn't call it a non-issue until you've verified the output has no excessive ripple. You can't see that with a dc meter. You need a scope set to ac and 200 mV/div. If that's flat, THEN there's no problem.
I am going to assume max ripple at max watts. Some data was provided except for your thoughts regarding max permissible ripple in relationship to near perfect <2.0 MV. You wrote you specialize in power supply design. So surely there must be a worry-point with regard to ripple on this section of the circuit.
Yeah I have to play 'Fraidy Cat because of where I live. In theory a strong bolt of nearby lightning can influence a hypersensitive circuit. So call me chicken. It depends on Salvo's answer. Max mv ripple permitted.
Might as well buy a couple of meters of shielded pair wire. Don't forget Niner your plastic rheostat itself is a coil subject to inductance. I have seen bad juju results of circuit resonance ringing and I ain't too keen on shortcutting and getting whacked by an inside straight.