parallax power supply 7345ru parts PWM

[Cstoliker]

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 they seamed more interested in selling me an upgraded replacement unit rather then parts to fix this one. Anyone know of a way to get a PWM for this? (Charging controller)
It's a retrofit from an original Magnetek 6345 wich was serviceable. Parts were available and the schematic is even available online. Unfortunately the 7345RU has non of theses things except for a "flow chart" and "installation instructions".

Or even if someone know enough about these to tell me how bypass the PWM and get full output to batteries. I'm not going to leave it plugged in but I'd be nice to be able to charge my batteries in a couple hours running off generator..

[Cstoliker]

Thanks pnichols, yea I understand the danger. I just wanted a way to charge the battery's faster when generator is running. 15v is relatively safe, no worse then driving my Buick which runs at 14.9-15.1vdc.
I may reduce it to 1 diode but I'm interested to see how this set up performs .

[Cstoliker]

NinerBikes wrote:


How do you think the propane gas is ignited, controlled or temp controlled and shut on or off, when running off the batteries? By a 12 V electrical controller.

I would think that the subject matter discussed in this topic would show that I am NOT electronic illiterate.

There is NO. I repeat NO 12v power source going to the fridge. I installed it. I would know. When on gas it has a pilot light and thermocouple. It's not a newer over complicated model. In fact it predates my RV by at least a decade. It's simple and just works.
But I can understand why you may think it was an electronically controlled model.

[pnichols]

If I were to mess with our 7345 converter's feedback loop, one approach I might use would be to bump up it's feedback reference voltage to only around, say, 14.4 volts and then move it's feedback sense point to the battery post.

That way one would get a solid 14.4 volts right at the battery for all the way up to a battery charge current acceptance rate of the maximum of the 7345 ... supposedly around 45 amps. However, one would have to be careful to only have the converter connected to the batteries for a few hours to prevent boiling away the battery water ... while also taking care of the safety factor via combining of cable fusing with not using too-small cabling ... so as to prevent cable over-heating. This is because a charger with a feedback loop sense point at the batteries will maintain it's voltage on the batteries with even a very small cable size running between the charger's output and the battery terminals - so in this situation the battery being charged could accept up to the charger's full current regardless of cable size - which could start fires.

That's why I mentioned earlier the "ultimate" charger being a multi-stage one with it's feedback sense point at the batteries to guarantee full spec stage-voltage right at the battery - if - there was adequate cable-path fusing and cable size to eliminate the heating danger.

I'm guessing -> but I'll bet most charger manufacturers in general do not use remote sensing for at least the three reasons of 1) the additional material expense, 2) the additional installation/hookup complexity for users, and 3) the danger liability introduced from users maybe using interconnection cabling too small for what the batteries are accepting due to the voltages that the chargers will guarantee gets established on battery terminals regardless of cabling size and current flow. Remember, there is no cable resistance voltage drop seen by the battery terminals with a charger utilizing remote sensing.

[NinerBikes]

Cstoliker wrote:
The fridge runs on gas or 120vac. Not 12vdc.
Most things in the RV will be fine with 15. That's what most cars run.
Besides, it would be for short bursts of time only.

How do you think the propane gas is ignited, controlled or temp controlled and shut on or off, when running off the batteries? By a 12 V electrical controller.

[Cstoliker]

Nice, that looks like the same as the voltage meter I installed in the console.

Thank you Sal, you did the hard work. All I did was read your schematic and build a circuit 🙂

[Cstoliker]

The fridge runs on gas or 120vac. Not 12vdc.
Most things in the RV will be fine with 15. That's what most cars run.
Besides, it would be for short bursts of time only.

[Salvo]

Nice work.

You really need an amp meter is see what the converter is doing.

http://www.ebay.com/itm/LCD-DC-100A-Digital-display-LED-Panel-Ammeter-amp-Ampere-Meter-100A-75mV-shu...

[NinerBikes]

15.4 is right at the edge of roasting your circuit board on your refrigerator, if it gets that high ever at the batteries. Dometic says 15.0V FYI. I've seen others quote 15.4V YMMV.

[Cstoliker]

Last pic: with no load: battery's disconnected I got 15.4 @ 7345 output.
This was taken almost immediately after the 7345 was plugged in and the battery's are down a bit.

[Cstoliker]

Voltage at 7345


Voltage at farthest battery. Note: sense wire is not yet trimmed. Have more then 10ft coiled up so resistance is high.


Turbo mode-sence wire disconnected.

[Salvo]

You'll need some insulation around the exposed resistor lead up in the air. You don't want that to short!

Cstoliker wrote:
Now I just have to iput it back togeather.

[Salvo]

The forward voltage drop of a diode is current dependent.



At 0.1 mA bias current, the diode drop is closer to 0.5V. It doesn't take much current to influence the error amp resistor divider. My recollection is you'll get 0.4 to 0.5V increase in converter output voltage. Go ahead, build it up and see what you get.


Sal

Cstoliker wrote:
It's silicon. Forward voltage drop is rated at 0.6v. So two in series should cap the voltage at 1.2v above max. So 15vdc. That's about perfect!

[Cstoliker]

Now I just have to iput it back togeather.

[Cstoliker]

Yes. I intend to keep the sense wire in place most of the time. But also install the "turbo button" I mentioned pages ago :-).
I'll install the button with a bright light that will be hard to miss. Should default to 15v when button is off.