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jyanof · 06-02-2009, 01:08 PM

For current sensing up til now, I've used a handheld DC clamp ammeter. It's pretty slick and has made my life a lot easier in many situations. For the future, I picked up a hall effect sensor to measure current:
838-L03S050D15

I haven't hooked it up yet, but that's the plan.

Yeah, the 555 timer setup definitely is still a 'dumb' configuration. The chip you show looks intriguing - what are you planning to use? This still needs hardware compensation to adjust the feedback loop to make it stable. Maybe it's easy to do, but it scares me! I'm hoping that it's easy to accomplish with software in the micro.

I agree about the safety issue! I bet that including a fuse in the output and a breaker in the input will solve some problems. There's going to be A LOT of current if it freezes on, so something will blow before the batteries get fried. In fact, the mosfets failed ON during one of my previous tests with the ST mosfet - The rectifier blew and shorted and then the main breaker (which is a dedicated 240V line) tripped. So, every electrical component (except the caps) failed.

I've debated putting hardware over-current protection like Paul has in his car controller. I don't think it's necessary since a charger is a much more benign application than a car controller - less changes in current, voltage, load, etc. I think just a fuse is good enough over-current protection.

I thought about the micro freezing at some PWM state and never shutting off. That could fry the batteries if it stays on all night. I guess robust code could help here. I also thought about having a manual timer switch (something like a dial you see at spas) that disconnects the charger after a certain amount of time. You'd have to be a little smart about how long you're charge should take, and it still may fry the batteries for a little bit, just not as long. If I had lithiums, I'd be really concerned about this.

Any other ideas? I haven't thought too much about failure protection.

06-02-2009, 01:08 PM	#76 (permalink)
jyanof Joe Join Date: Feb 2009 Location: phx Posts: 260 Thanks: 0 Thanked 48 Times in 38 Posts	For current sensing up til now, I've used a handheld DC clamp ammeter. It's pretty slick and has made my life a lot easier in many situations. For the future, I picked up a hall effect sensor to measure current: 838-L03S050D15 I haven't hooked it up yet, but that's the plan. Yeah, the 555 timer setup definitely is still a 'dumb' configuration. The chip you show looks intriguing - what are you planning to use? This still needs hardware compensation to adjust the feedback loop to make it stable. Maybe it's easy to do, but it scares me! I'm hoping that it's easy to accomplish with software in the micro. I agree about the safety issue! I bet that including a fuse in the output and a breaker in the input will solve some problems. There's going to be A LOT of current if it freezes on, so something will blow before the batteries get fried. In fact, the mosfets failed ON during one of my previous tests with the ST mosfet - The rectifier blew and shorted and then the main breaker (which is a dedicated 240V line) tripped. So, every electrical component (except the caps) failed. I've debated putting hardware over-current protection like Paul has in his car controller. I don't think it's necessary since a charger is a much more benign application than a car controller - less changes in current, voltage, load, etc. I think just a fuse is good enough over-current protection. I thought about the micro freezing at some PWM state and never shutting off. That could fry the batteries if it stays on all night. I guess robust code could help here. I also thought about having a manual timer switch (something like a dial you see at spas) that disconnects the charger after a certain amount of time. You'd have to be a little smart about how long you're charge should take, and it still may fry the batteries for a little bit, just not as long. If I had lithiums, I'd be really concerned about this. Any other ideas? I haven't thought too much about failure protection.