What a friggin convergence of knowledge!Yes, with a dual parallel mod flipping one battery results in a direct short. The board should be fine though. A simple diode is no good for reverse battery protection because you have a .7V drop across it. You could do it with a mosfet and get it down to a few millivolts though.
That's why I use fets for reverse polarity. No bridge, but you can get voltage drop down to 3 or 4 millivolts.
Boy oh boy - Kiwi, You must have brass Gazongas to give the reverse bat protection a try after all the problems you had with your first VF.
By the way if you put the batteries in one at a time and look at the display before putting in the second battery you should also be OK even with the V.F. Then you are only testing the reverse polarity protection of the DNA40 and not the max current flow between to 35 amp batteries.
Surrounded by EEs. HA! Loving it!
@AMD - I'm a little embarrassed that I didn't ask you this in my first post /sigh Are you OK physically? I hope. I wish. That's the #1 issue IMHO.
Actually no test circuit needed. With a p channel you can wire the drain and gate across the battery and use the source to feed the positive side of the load (gate and negative side of the load wired together to the negative of the battery). Or flip it and use an n channel. When the battery is right the gate will be pulled high relative to the source and turn on, if it's backward it'll turn off and protect the load. At our voltages an Si4838DY works perfect. At 2V it's only .003 ohm and handles 60 amps.rusirius,
Ah Grasshopper it is hard to keep good German engineering down.
Actually I think that is how most reverse bat protection is implemented. A circuit to test polarity and when that circuit decides everything is OK it turns the FET on which puts power to the controller board.
Actually no test circuit needed. With a p channel you can wire the drain and gate across the battery and use the source to feed the positive side of the load (gate and negative side of the load wired together to the negative of the battery). Or flip it and use an n channel. When the battery is right the gate will be pulled high relative to the source and turn on, if it's backward it'll turn off and protect the load. At our voltages an Si4838DY works perfect. At 2V it's only .003 ohm and handles 60 amps.
VS was no better.
This is very unfortunate...and the price we pay for participating in a still nascent commercial space.
After very specifically detailing their reverse polarity "problem" with the rDNA 30 (how their battery position invites reverse polarity relative to other mods...pointing out the warning VF provides, & etc.) they declined a free fix...then added a warning to their web site, but not their insert card--where both should have been there from the get go. In any other commercial space a law suit would have been instantaneous, the trivial amount of cash involved. notwithstanding.
Okay!, I learned my lesson; I'll NEVER do THAT again.
If it doesn't work that way, where does the energy go? To make the math easy, let's say you had a 1.7V DC source. You put a diode with a 0.7V drop in series with a 1 ohm resistor as a load across this source. Your source is putting out 1A at 1.7V -- that's 1.7 watts. The resistor sees 1.0V and therefore dissipates 1.0 watts. So where did the other 0.7 watts go? If it's not being dissipated in the diode, it has vanished. Energy does not vanish.
