parallax power supply 7345ru parts PWM
My 7345 is not charging the coach batteries but does supply 12power to all accessories. The transformer, fan and relays work fine. Think i need a PWM circuit for it. Contacted PP tec support and th...
Forum Discussion
Notice in Sal's 7345 schematic above the "8 awg" wire he shows going between "Vout" (the 7345's output terminals) and the two 12 volt RV batteries in parallel with each other.
Here's a simplified explanation of a potential danger in using a circuit modification like this without the proper charging current flow constraints: His modification will force full 7345 output voltage (as set by the error circuit parameters and components) unto the batteries' terminals REGARDLESS of the gauge of the wire between the 7345 and the batteries. Whatever the batteries will accept, current-wise, with full 7345 voltage (as set by the circuit parameters and components) onto their terminals is what will flow through this wire regardless of the size of the wire.
For example, with real run-down batteries they might have a charging current acceptance rate of 45 amps. Then 45 amps will be forced to run through this wire by the 7345 with any voltage drop occurring in this wire being compensated for by the 7345 trying to go to very high terminal voltages (the "Vout" point in Sal's schematic) in order to maintain this current flow into the batteries.
The danger comes in having wire too small between the 7345 and the batteries. Too small wire with 45 amps flowing through it could of course heat up and catch fire. Remember, again, that this circuit modification over-rides the "automatic and natural" current limiting situation that results from the voltage drop in too small wire reducing the voltage on the batteries' terminals which in turn reduces their current acceptance rate ... since this modification will always keep the voltage constant (no sagging) on the battery terminals.
For this mod to be perfectly safe, the wire between the 7345 and batteries should be fused at a value to limit current flow to a value that will not cause excessive heating in whatever size wire is installed between the 7345 and the battery(ies).
Here's a simplified explanation of a potential danger in using a circuit modification like this without the proper charging current flow constraints: His modification will force full 7345 output voltage (as set by the error circuit parameters and components) unto the batteries' terminals REGARDLESS of the gauge of the wire between the 7345 and the batteries. Whatever the batteries will accept, current-wise, with full 7345 voltage (as set by the circuit parameters and components) onto their terminals is what will flow through this wire regardless of the size of the wire.
For example, with real run-down batteries they might have a charging current acceptance rate of 45 amps. Then 45 amps will be forced to run through this wire by the 7345 with any voltage drop occurring in this wire being compensated for by the 7345 trying to go to very high terminal voltages (the "Vout" point in Sal's schematic) in order to maintain this current flow into the batteries.
The danger comes in having wire too small between the 7345 and the batteries. Too small wire with 45 amps flowing through it could of course heat up and catch fire. Remember, again, that this circuit modification over-rides the "automatic and natural" current limiting situation that results from the voltage drop in too small wire reducing the voltage on the batteries' terminals which in turn reduces their current acceptance rate ... since this modification will always keep the voltage constant (no sagging) on the battery terminals.
For this mod to be perfectly safe, the wire between the 7345 and batteries should be fused at a value to limit current flow to a value that will not cause excessive heating in whatever size wire is installed between the 7345 and the battery(ies).
