Connecting two different power sources together

[motorhome]

I have two power sources feeding a max 30 amp load.
One source is 13.2v the second is 14.2 volts.
The first source is always connected the second source is only turned on now and again.

The problem is the second source voltage cannot feed into the first source. I was looking at fitting a diode on the first source to the load but the current is so high the diode would probable burn out.

So would a PMOS work and if so will the attached circuit work,

Bit more detail about the circuit.
This is a motorhome with a lithium battery (first source) which is feeding into the electronic block with a build in charger (second source) the built in charger cannot charge the lithium as the profile is all wrong. I could just remove the power supply to the electronics block but I would then loose the function that it charges the vehicle battery. So it would be nice to block the charger from charging the lithium but allow it to charge to vehicle battery.

 

[Bluejets]

Changeover relay/contactor.

 

[motorhome]

Changeover relay/contactor.

The only way to do that would be to install a 240v coil relay with 30amp contacts. Would be about £30 contactor. This is a way to do this but I was looking at a cheaper way using discrete components

 

[motorhome]

Also by adding a contactor in to remove the lithium all together then the charging controller will take on the full van load of 30 amps. It is only rated at 20 amps and parallels the load with the van battery

 

[Bluejets]

You will need to provide a more detailed sketch of the entire arrangement.
No good providing a small section and then shifting the goal posts whenever a suggestion is made.
Using a 30 pound contactor on , for arguments sake, a 30,000 pound motorhome doesn't seem to high a cost to me at least.

 

[motorhome]

You will need to provide a more detailed sketch of the entire arrangement.
No good providing a small section and then shifting the goal posts whenever a suggestion is made.
Using a 30 pound contactor on , for arguments sake, a 30,000 pound motorhome doesn't seem to high a cost to me at least.

Actually I thought the question about the circuit was accurate about the MOSFET and would it work correctly as a blocking source and still allow the 30 amps to pass through when the second source is not provided.

My reply was not about worrying about cost it was just that I was seeing if my idea would work.

I could buy a normal car charger just charge the vehicle battery from that.

By keeping the vans electronics block in use under electric hook up I gain a few more things like taking on some of the load, electric hook up indication and vehicle battery charging.

If my MOSFET design would not work then I will look at alternative ideas. All I was saying in my reply was I looked at a relay solution and I gave the reason why this would not work. I did not shift the goal so sorry if this annoyed you

 

[Bluejets]

Well if you have no intention of supplying sufficient information then it is near impossible to say.

 

[Harald Kapp]

You could use an "ideal diode" circuit e.g. from TI or from AD.

 

[WHONOES]

You could Diode OR the supplies together using Schottky recitfier diodes.such as the VS-100BGQ-100 that is rated at 100V and 100A with a forward drop at 30A of 700mV or, if you can guarante that the supplies will never exceed 15V you could use the VS-!00BGQ-15 that is rated at 100A but only 15V. Its advantage is a lower forward drop of abot 350mV at 30A. the chosen devices would nee to be mounted on a small heatsink as they will dissipate between10 to 20 Watts.