PWM Circuit for AGM Battery Charger 2

[Jacques2014]

Hi, For different reasons, I am designing a custom battery charger for an 12Vdc 100amps AGM battery. I use a PWM control circuit, but the driving Mosfet tend to heat a lot. The actual circuit simply switch the input DC source (solar panels) using a power mosfet directly in the battery trough diodes. I tough that adding a coil between the mosfet output and the battery may help to lower the heat dissipated but the mosfet. I need help figuring out how to compute the proper inductance value in relation with my switch frequency. So any help will be welcome. Maybe I am wrong, and the coil will not help at all. Your input will be welcome. Input DC voltage vary from 12 to 22Vdc approximately while the battery will peak around 15Vdc, I try to keep current constant using the PWM. The circuit is working, but heat a lot. Peak current may raise to 10amps when running in bulk charge.

Bye
Jacques

 

[Sparweb]

Hi Jacques,

Are you building this from scratch without referring to tried-and-true designs?
When Xantrex built their C40 solar charge control / voltage regulator system (in the 1980's) they went with IGBTs, not MOSFETs.
Everything you want your controller to do, is about 1/4 of the functions possible in the Xantrex device. You can still buy them for about 50 USD.

If you want MPPT, then get a Tristar for a little more money, and it has 2x the functions as the Xantrex C40.

STF

 

[Jacques2014]

Hi everybody,

First thanks for all the comments, every thought is useful.

Reading your ideas, searching the internet, thinking about the current design make me realised that my actual concept may not be the best way to go for my application.

The thread starts while I was thinking to add a coil to the design in the hope to raise effectiveness. Heat is annoying and a lost of energy in this case. My design requires the best energy use possible.

My goal is to have the possibility of turning the charger to charge or float mode and use the maximum energy possible from the solar panels, while not producing unwanted heat in the process.

From all the thoughts, what is appealing to me is the idea of using a Buck-Boost switcher. I found one example using a LM5118 that please me. This concept should be a lot more efficient and should not produce a lot of wasted heat. It will change the battery even if the solar voltage is under 12Votls, so using every watts available even if it’s not much.

I add the schematic to the thread, I found it on internet, I do not know who done it, but it is now public.

Please comments on the idea, I may try to build this for experimentation.

Bye
Jacques

 

[Jacques2014]

The attachment is not working again, so here another one, maybe this one will work. I change from PNG to JPG.

Bye
Jacques

 

[OperaHouse]

Most designs on the internet are pretty bad by people who don't know what they are doing. I can conceive of no reason why you would ever want to use a buck boost converter. Voltage should never drop below the panel power point. This isn't really that hard if you are not making thousands of them and trying to get every penny out of the design.