Update- I have done some fine tuning. It turns out that I am now able to charge to 300V in under 1 second with a 12V NiMH battery pack. That will save the cost of 2 cells, and also allows for a slightly smaller voltage rating on other parts. The heat sink on the mosfet is slightly warm. The hottest it has gotten is 55C.
With several minutes of repetitive charging from 0 to 300V, there is some stuttering in the circuit. At this moment, the heatsink is fine, but the PTC that regulated the current is very hot. It was 80C+. This is pretty much the max temp for the PTC.
I have tested the current draw. For the most part, it stays in the 3-5A range for the total circuitry. This is what passes through the PTC. I looked at the datasheet, and it was one of those things where the website search was misleading.
The "max current" was 7.5A. I thought this was reasonable. But nope.... the operating current is actually .75A with a trip current of 1.5A. I think what was happening is that it was heating up from over use, which increases the resistance, which increases the heat....and then it starts the stutter process.
Can you tell me something?
If my circuit typically draws no more than 5A, what size of PTC should I get? Say I get a PTC with an operating current of 7A is is fine to have that very brief 20A spike?
If my circuit goes out of whack, I think it will go way over 7A, but I dont know what range causes a safe shut off, yet does not affect a normal surge. I am also concerned I may see some other issues once a higher rated PTC allows more current in ;-)
With several minutes of repetitive charging from 0 to 300V, there is some stuttering in the circuit. At this moment, the heatsink is fine, but the PTC that regulated the current is very hot. It was 80C+. This is pretty much the max temp for the PTC.
I have tested the current draw. For the most part, it stays in the 3-5A range for the total circuitry. This is what passes through the PTC. I looked at the datasheet, and it was one of those things where the website search was misleading.
The "max current" was 7.5A. I thought this was reasonable. But nope.... the operating current is actually .75A with a trip current of 1.5A. I think what was happening is that it was heating up from over use, which increases the resistance, which increases the heat....and then it starts the stutter process.
Can you tell me something?
If my circuit typically draws no more than 5A, what size of PTC should I get? Say I get a PTC with an operating current of 7A is is fine to have that very brief 20A spike?
If my circuit goes out of whack, I think it will go way over 7A, but I dont know what range causes a safe shut off, yet does not affect a normal surge. I am also concerned I may see some other issues once a higher rated PTC allows more current in ;-)