My point would be that we can often find better value if we know what an item does.
In this case the idea is that we have a point "A" where we have the converter to charge the coach batteries and keep them at a float level. Then we also have a point "B' at the chassis battery where it would be handy to have some automatic way to let it get some charge from the coach system.
For simple , we want to let point "A" also charge and maintain the voltage at point "B" with minimal equipment! We want it to allow current to flow from A to B but we don't want current to flow B to A as that would risk running both sets down and leaving us stranded.
That leaves the first big question of what we can put to connect A and B that does what we want? Then we want to apply a few basic specs to find the correct item that does that.
So we want something that lets current flow in only one direction. That is a diode!
AI is beginning to be an item which I find handy for the quickie answers:
Then we might want the current to start flowing when the chassis battery voltage gets down to some level. Maybe a 1/4 to 1/2 volt lower than the coach float voltage?
We also want this to be pretty solid and not likely to fail if the voltage gets very far above the "normal" 12-14 volts. Maybe we buy a type that is rated for max of 20 volts for a bit of safety factor.
Do you want to go the extra mile and build in an LED to tell you when it is connected ? If I put the gizmo back in some compartment, I don't consider going back to check to see if it is working if I hard wire it in the circuit, so I leave that "feature ' out!
Then if we are building this for our personal use, we likely want the parts to be cheap enough to factor in our labor to build it and still come out ahead?
If the commercial product is now near $99, we have some slack!
It might take buying a few different diodes to try and see exactly what the voltage does while we store the RV? No point in putting too much faith in our table top engineering!
Maybe step down to Mouser, etc. and buy a half dozen of a few selected types if they are cheap enough? Per item they get cheaper if you buy more!
This seems to be cheap enough to fit my budget, even with the unknown of tariff added! How much is the tariff on 36 cents?
And DO keep in mind that you have to find a couple feet of wire and a plastic bag to insulate it?
OR maybe go high class and cover it in heat shrink?
Maybe if we put it on the two big lugs of the mode solenoid which is usually in a dry space where we don't need a box or insulation?
The big expense you will likely want to avoid is the legal things about patents, etc. and the expense of adverts and sales folks if you sell it to others.
I like to keep alternates on hand for different situations and this is just what I might do if I needed one!
When I gamble I try to keep it at a very low level, so 36 cents seems like one I might try!
