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..

[Chris_Bryant]

The 7345 uses PWM to regulate the voltage, but it is not a charger- it is a fixed voltage unit- 13.6 - 13.8 volts. It will never go above that. As was pointed out, there was a "T" option which raised the voltage for a fixed amount of time.

I suspect it is working as well as it ever will, to be honest. It will never charge quickly.

[KJINTF]

Can you see any defective parts?

Many times the caps are easily seen as defective and the resister pack is burned

[Cstoliker]

This is getting over complicated. Even the 7345 may have a resting voltage of 13.6 but the PWM should, at least in theory be able to get over 14v if it correctly senses the battery's are that low. OF coarse I can't even confirm the 7345 has a PWM charging circuit. The assumption is based on the 6300 series (wich it replaced did)
Realistically a 12v 50amp batter charger could be purchased for less then all these options. Start the generator, plug in the charger and off I go. Or even get an alternator connected to the generator's crank shaft 🙂

Large guage wire is definitely important though. The 7345 has 10 or 8 guage wire on it. But for a max of 45amp at a distance of less then 10feet should be sufficient.

I've got the unit out and disassembled. I'll order the parts. If it fixes it great, if not I'll buy a decent automotive charger.

[pnichols]

BFL13 wrote:
The 7355 in ours is 10 years old and still going strong. Great converter for when on shore power, but a slow battery charger due to the 13.8v and a long wire.

There is no charging circuit; the batts are just exposed to the 13.8 and you get whatever current the "spread" allows between batt voltage and 13.8--ie not much.

To get full current from the 7355 you can run it as a supply to batteries that are on an inverter which is running a big load. I ran a test of that where the inverter was drawing 90a from the batts as seen on the Trimetric. Used the 7355 with short fat wires to the batts and Trimetric showed minus 34a instead of minus 90a. This shows the 7355 was doing 56a. In its normal location on longer fat wire, with normal battery charging, I see 35 to 40a at most that tapers quickly.

For fast charging to keep gen time down I use higher amp, higher voltage chargers. (Phil, lots of them will do constant amps in bulk while the batts will accept them. PowerMax, Vector/B&D, Paramode, WFCO, Iota all will.

Interesting comments above!

Your mention of a long wire is spot-on. Winniebago installed my 7345 via about 8 feet (estimated - not measured) of 8 gauge wire, so the drop along it while topping up our 200 AH AGM battery bank can be as great as 0.2 to 0.3 volts, which of course gets added to the unfortunate output output sag of the 7345. Slight decreases in what a charging battery sees being forced onto it's terminals from a power supply can really slow down it's charging rate at certain points in the battery's charging cycle. I've fit samples of larger wire sizes into the terminals of the 7345 and found that it's terminals can probably take a wire as large as 2 gauge, so I should replace the 8 guage run between it and the batteries with a 2 guage run "one of these days". (My AGM batteries have, for almost 7 years now, reduced the urgency in doing this.)

Your comments on "forcing" a 7355 to full current output through use of an inverter to really drag on the main battery bank is enlightening. That means that the 73XX family of converters can indeed actually supply their full advertised current if conditions are right. Unfortunately, a partially discharged RV battery bank sitting at 12.1 volts isn't going to get/take that kind of current because of, as you say, too small of a voltage spread (difference) between 12.1 volts and 13.8 volts. That's the real reason that multi-stage chargers do better at charging than fixed 13.8 volt converters ... because of the high voltage range that's available on the multi-stage units. Also, that's why the Parallax 73XXT converters would have, in my opinion, made way better converters for motorhome use. It's too bad that Parallax discontinued that model line.

So .... regarding (affordable) chargers being able to supply full advertised current while maintaining full advertised voltage on their terminals .... are you saying, for example, that a 55 amp PD charger will measure around 14.4 volts right on it's terminals while a current meter is simultaneously reading 55 amps flowing out of it? If so, I apologize for my skepticism and will update my knowledge base. I might even have to revisit purchasing of a temperature compensating Paramode RV charger ... assuming of course that it can maintain full current at full voltage. 😉

[Cstoliker]

Does seam backwards to me too. While camping I got the battery's donn to around 11.8vdc (pretty
Much flat out dead. Let the generator run about 4 hours and battery did come up slightly but only to just over 12vdc. But by no means charged. I then started the RV's engine for about an hours and the voltage sat at about 13.45 to 13.5.. Battery then after sitting for about an hour was 12.45 maybe 85% charged.

The 6345 has a separated charging circuit and a lot of information is available for it. (PWM charger) and was a available without the charging option.. But the RetroFitted replaced 7345RU wich I have has almost no information available for it.

[BFL13]

The 7300 (and others) does sag under load and that includes the load of the battery charging.

You start out with the batts at 12.2 and the converter at 13.8 Connect them. Battery voltage spikes to 13.2 and converter at DC panel sags to 13.6 (say)

As the battery charges up, BOTH voltages rise, but the battery voltage rises more and eventually catches up to the converter's rising voltage when the batts are fully charged and amps have shrunk to zero flow. Batt and converter will now both be at 13.8 again, except the batt will be a tad lower due to your long wire.

But, with lights and fans etc, no way should the converter's voltage rise as you turn them on. That is backwards.

[Cstoliker]

Sounds reasonable. If I disconnect the battery, and with no load I see about 13.4vdc but when the battery is connected it goes down. And it's not because the power
Supplie is being drawn down or taxed by the battery. I saw almost no amperage flow between the converter and battery. But voltage will start going up depending on how manny accessories are turned on.

[Cstoliker]

Thanks. I took the unit out. Drilled the ribbets then noticed one of the heat syncs was warm. And battery's were at 12.7..... To I reinstalled the unit (shore power disconnected and now have every 12v power source on ( 8 lights, 2 exhaust fans, & inverter) trying to draw down the battery. Then I'll plug it in and see what happens
Can't imagine it jjust magically started working sine I had it out a few days ago but I did use an air compressor and clean it out so stranger things have happened..


Just running the last test before I start replacing components. 🙂

[BFL13]

Cstoliker wrote:
Yes. Voltage goes up as load is drawn. As per original post with battery's fuse in i may start somewhere in the 12.4 range depending in the battery state at the time.
If I turn on 3 or 4 lights, I can hear the 7345 come to life and voltage will increase to just over 13vdc. If I turn on everything 12v in the coach I can get the voltage as high as 13.8.

The 7345 works, aside from the charging portion, it simply does not see the battery as a load. You would expect most to loose voltage as their max current is reached. And i'm sure this would as wellI, i just can't draw that much off of it.

Your 7345 is not working right, so it does need the recommended repairs.

The 7300 puts out a steady 13.8v no load, but with no battery connected, when running 12v loads, you see an increasing sag in "loaded voltage" measured at the DC panel, with increasing 12v load

I ran a test on that, posted somewhere a while ago. With everything 12v in the rig on ISTR voltage got down to 13.2 It did stay above 13.

The 7355 in ours is 10 years old and still going strong. Great converter for when on shore power, but a slow battery charger due to the 13.8v and a long wire.

There is no charging circuit; the batts are just exposed to the 13.8 and you get whatever current the "spread" allows between batt voltage and 13.8--ie not much.

To get full current from the 7355 you can run it as a supply to batteries that are on an inverter which is running a big load. I ran a test of that where the inverter was drawing 90a from the batts as seen on the Trimetric. Used the 7355 with short fat wires to the batts and Trimetric showed minus 34a instead of minus 90a. This shows the 7355 was doing 56a. In its normal location on longer fat wire, with normal battery charging, I see 35 to 40a at most that tapers quickly.

For fast charging to keep gen time down I use higher amp, higher voltage chargers. (Phil, lots of them will do constant amps in bulk while the batts will accept them. PowerMax, Vector/B&D, Paramode, WFCO, Iota all will. PDs are the ones that don't quite in most cases reported here, except somebody got his to do it--forget details on that exception)

[KJINTF]

Yes - PCB aka Printed Circuit Board

The resister pack gets VERY hot you will find 5 resisters in parallel standing up off the board a bit - the pcb traces under them get burned up - a simple fix is to solder a wire onto the pcb and the resister leads to replace the burned traces.

The small cap is a 2,700ufd @25Vdc rated at least 105C
The large ones 1,200ufd @250Vdc

[Cstoliker]

Pcb under the resistor pack? You mean the printed circuit board? About all I could do with that is check the continuity of the printed connections and run jumpers if any are found bad,


I'll go rip the thing out in a few minuets. Hopully I can get the parts today and bring my de-soldering iron and soldering iron to work (I have a lot of free time at my job) and get to work. Caps aren't expensive I'll just replace without testing.

[KJINTF]

I attempted "back tracing" on several occassions, after a few dozen repairs of the exact same unit and seeing the same issues each time. Suggest you get a good ESR meter check the two large 250Vdc caps replace the small cap in the picture and rebuild the pcb underneath the resister pack - you should be good to go. Only had one 7345 over the years which must have been plugged into 240Vac with blown FETS.

Good to hear you will be repairing rather than replacing.

[Cstoliker]

I'll do the repairs. I'm quite good with electronics and have all the equipment. Only problem is they don't supple a schematic of the particular unit so it takes a while too back trace the components to figure out what does what.

[KJINTF]

Have you removed it from the rig yet?
Drill out the pop rivets and remove the four screws holding the PCB in place replace the caps and rebuild the current sense resister network - it's a really simple job - all you will need is a small drill, #2 Phillips screw driver, soldering iron and the replacement parts.
Should not take more than 20 or 30 minutes and cost less than $5.00 for the entire repair.

Unless you want to spend $150.00 or more on a replacement
If you do decide to replace rather than repair I would be happy to take the 7345 off your hands - as I said earlier they are wonderful high current 12Vdc shop supplies and with a 100 amp diode in series they can be great a winter time battery maintainer suppling 13.2 volts to the battery bank.

[Cstoliker]

Yes. Voltage goes up as load is drawn. As per original post with battery's fuse in i may start somewhere in the 12.4 range depending in the battery state at the time.
If I turn on 3 or 4 lights, I can hear the 7345 come to life and voltage will increase to just over 13vdc. If I turn on everything 12v in the coach I can get the voltage as high as 13.8.

The 7345 works, aside from the charging portion, it simply does not see the battery as a load. You would expect most to loose voltage as their max current is reached. And i'm sure this would as wellI, i just can't draw that much off of it.