Mar 112017
 

So, having knocked the regulation on the LDOs down a few pegs… I am closer to the point where I can leave the whole rig running unattended.

One thing I observed prior to the adjustment of the LDOs was that the controller would switch in the mains charger, see the voltage shoot up quickly to about 15.5V, before going HOLYCRAP and turning the charger off.

I had set a set point at about 13.6V based on two facts:

  • The IPMI BMCs complained when the voltage raised above this point
  • The battery is nominally 13.8V

As mentioned, I’m used to my very simple, slow charger, that trickle charges at constant voltage with maximum current output of 3A. The Xantrex charger I’m using is quite a bit more grunty than that. So re-visiting the LDOs was necessary, and there, I have some good results, albeit with a trade-off in efficiency.

Ahh well, can’t have it all.

I can run without the little controller, as right now, I have no panels. Well, I’ve got one, a 40W one, which puts out 3A on a good day. A good match for my homebrew charger to charge batteries in the field, but not a good match for a cluster that idles at 5A. I could just plug the charger directly into the battery and be done with it for now, defer this until I get the panels.

But I won’t.

I’ve been doing some thought about two things, the controller and the rack. On the rack, I found I can get a cheap one for $200. That is cheap enough to be considered disposable, and while sure it’s meant for DJ equipment, two thoughts come to mind:

  • AV equipment with all its audio transformers and linear power supplies, is generally not light
  • It’s on wheels, meant to be moved around… think roadies and such… not a use case that is gentle on equipment

Thus I figure it’ll be rugged enough to handle what I want, and is open enough to allow good airflow. I should be able to put up to 3 AGM batteries in the bottom, the 3-channel charger bolted to the side, with one charge controller per battery. There are some cheap 30A schottky diodes, which would let me parallel the batteries together to form one redundant power supply.

Downside being that would drop about 20-25W through the diode. Alternatively, I make another controller that just chooses the highest voltage source, with a beefy capacitor bank to handle the switch-over. Or I parallel the batteries together, something I am not keen to do.

I spent some time going back to the drawing board on the controller. The good news, the existing hardware will do the job, so no new board needed. I might even be able to simplify logic, since it’s the battery voltage that matters, not the source voltages. But, right now I need to run. So perhaps tomorrow I’ll go through the changes. 😉