DIY auto alternator charge controller advice

[madlabs]

Corenlius,

I don't think you'd have to get rid of the engine shut off relay. That's what I was talking about dual purposing the pins, so that you could have your cake and eat it too. Use the temp. switch as an input when the device starts up, then once running uses it for a serial display. It being a digital only pin is fine. I gather that you can debug via a PC though, so the LCD not so big a deal for you. I'm going to try the same scheme on several of my pins so that I can fit all the features I want into my 13 I/O.

As to the relay, here is what I am doing. It uses one DPDT realay. The NO side is connected to the GND of the  voltage regulator. The NC side is connected to the motor shutdown wire and the COM is connected to ground. To start the device, hold down a switch that activates the relay. The first thing the uC does is send a pin high conected to a transistor which then holds the relay open. When done charging it sends the pin low, kills it's own power and kills the motor. That way there is no battery draw after you are done charging. And every watt counts!

Jonathan

[bvan1941]

MADLABS,
Very elegant solution!!
Bill

[Cornelius]

The point is, Jonathan, that the available digital pin are INPUT only.

I like your relay solution...

[madlabs]

Thanks, Bill!

And Cornelius, proving once again I should read more carefully, you did state digital IN only in your post. And I'll never get the time back that I spent rexplaining something you already understood. But you have the PC debug, so no big deal anyway.

I'm going over to my buddy's place tomorrow, the one with the CNC. He is going to help me get going with the CAD program. Will be sweet to be able to make up PCB's with ease, I've only done them the old school ways.

Jonathan

[madlabs]

An update on this project:

I'm out in the shop watching the new controller circuit run my generator! It's running well so far. Right now I'm cranking 140 amps into the bank and am approaching 14.4V, so I'll get to see it ramp down the current soon. Current and voltage sensors working smoothly so far. The circuit is still on the breadboard and lacks a few things, like zener protection for the ADC input connected to the battery bank, but I can really get to work on the board layout. Lots of code stuff left to do, but I'm going to focus on the PCB and worry about the software side later.

Thanks for all the help!

Jonathan

[Cornelius]

What pwm frequency are you using for the field right now?

[madlabs]

Was using 1.5kHz yesterday, for no particular reason other than the day before I had been playing with how low I could go and still get smooth adjustment. I'm gonna drag a scope out to the shop next time I have a chance to play and look at the field transistor's wave form and see the effect of various PWM freqs.

Aside from a couple of random resets (due to breadboard & lack of decouple caps I'm guessing) it ran well and did a complete charge cycle yesterday.

Jonathan

[Cornelius]

I'm just asking, because the only experience i have with pwm are driving a couple of Mosfets via a mosfet-driver; driving a dumpload of 28A. I had no experience with mosfet/pwm, and getting the mosfets happy was a challenge... It all came down to the driver and the pcb design. In the beginning, i drove the mosfets directly from the pic output; it worked, but the mosfet was getting terrible hot, even with low loads, and the scope pic was terrible.

After burning up 5-6 drivers (which are cmos devices; d*mn sensitive buggers...), i finally got it right; i even added ferrite beads on the gate resistors etc., and now the fets are running lukewarm @ 28A; max load: 100A+. (2x IRFZ48) The scope pic are now square as a cube; both at the gate and the drain.

In the beginning i ran @ 16kHz, which seems fine at the moment (without driver circuit), but in my quest to reduce heat in the mosfets (still without driver), i ended up with 4kHz; that's what i'm still running, but i'm seriously thinking on changing it to 20kHz++, because when the dumpload are active, some of my led-lights are humming with a VERY irritating 4kHz noise!

Though; with a gasoline gen running, charging a battery, that wouldn't be a problem. And heat in a transistor usually rises a bit with higher frequencies...

Now, that was a bit of a rant... Sorry...

[madlabs]

Cornelius,

Yeah, thise are the kind of reasons I went with Darlington transistors on this one. The load is small so the transistors can handle the job and it kept the layout less critical.

Do you have a PCB for the 28 amp dump load? Might be fun to try and convert that to a DIY MPPT.

Hope to play with the controller freq. today.

Jonathan

[Cornelius]

I made the pcb for the dump load the manual way, by drawing the traces with a permanent marker pen and etched it, so - no digital layout.

But it's Very similar to Frackers Dumpload board over at the Other forum, except i use a different driver and fets, but same layout. (He just wrote an update on his project.) (I dare not link yet... )

[tomw]

(I dare not link yet... )

Ccornelius;

Well, in my humble opinion:

Linking to valuable content anywhere is not a problem. Especially for anyone actively involved here. You qualify  .

Tom

[Cornelius]

Huh; seems that i'm a bit confused today... Frackers posted the story here.

http://www.anotherpower.com/board/index.php/topic,237.0.html

[Wolvenar]

I second Toms opinion