A better low cost power converter?

[booster]

There have been a few threads by folks that understand the importance of better charging of batteries, especially when going to more and better batteries.

As far as I know, the only ones that can do a good job are the Magnum products with the monitor and fancy remote kits, and Progressive Dynamics with the add on Charge wizard, plus a monitor like a Trimetric.

The Magnums work automatically off battery amps to control charging, but are at least $1000, depending on the model. The PD chargers are much cheaper, even when you add a monitor to them, but you have control them manually off the monitor readings.

Two of the lower priced converters that have been mentioned lately were the Xantrex and Samlex. Both use amps to control the charging, but it is internal to the charger, so loads mess it up, and you can't set the amps to match your batteries.

I am not an electrical designer, so I have no idea is either one of them could be modified successfully, but there are some much more electrically inclined folks on here, for sure, so it can hurt to ask.

What I think might work:

Tap into the output power from just before the point where they are measuring the current, and run it to another output. The Xantrex has multiple outputs already, diode protected, so you would already have the terminal in the case to use for the second output.

Connect any loads you would have to the new output, so the current measuring wouldn't see them in the charger, but it would see the other output to the batteries.

Add a relay or manual switch so you can connect the two outputs when you were not on shore power, so you get battery power to the coach. If you forgot it on or had a relay failure, it wouldn't hurt anything, just be back where you started.

Determine how they are measuring the current (maybe voltage across a diode or resistor?) and duplicate it how it works at whatever it would take to make it adjustable with DIP switches or such for as many amp settings as you would want.

All the rest should be able to stay the same in the charger---maybe?

What think the electrical wizards about this?

[papab]

Sounds great, in fact all I need is the last part about messing with the current sensing. I don't typically have any significant loads for very long. The fridge only runs about 30%.
If they use that same measurement for current limit control you might overload it?

[booster]

Originally Posted by papab

Sounds great, in fact all I need is the last part about messing with the current sensing. I don't typically have any significant loads for very long. The fridge only runs about 30%.
If they use that same measurement for current limit control you might overload it?

I hadn't thought of that, but I suppose it is possible. My guess would be that it would not be an issue, though, because the one reading is used to trigger a change, it is likely a fixed single setting. I have never heard how the chargers actually limit the maximum charging amps, but from a specs and such, I would think they are trying to pull out all power they can so there would be very little if any capacity above rated. Probably would be a regulated power supply in early stages of the charger to protect downstream parts, so wouldn't be affected by the actual output setting.

You might even be extraordinarily lucky and find the transition amps are settable off a pot. It is a possibility as they make very similar chargers in different capacities so they would have different transition amp settings needed on them. If they use the same control board for the chargers, and change output with a separate output power board, it would make sense to have the pot so all the control boards would be identical for cost and simplicity.

Of course, all of this is total and pure speculation.