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..

[Salvo]

Paralleling the 7345 with another charger in order to increase current won't work. The higher voltage source will do all the work. The lower voltage source will be back biased. But, if you like kluges, go for it.

Regarding your claims that the mod has the potential of starting a fire within the cable. I see now you're backing off a bit. Now you're saying the cable must be undersized. Here's a quiz question for you. At 45A, what's the largest gauge cable that will start a fire? We'll assume if you don't provide an answer then it's not an issue.

Sal

pnichols wrote:

In the final analysis, your mod is a great hobby project to demonstrate getting around a product's deficiencies. In the long run, I'll probably do what MEX and BFL13 do - use an inexpensive high voltage charger in parrallel with a 7345 to up the current a bit when charging my AGM batteries, as they charge so fast anyway even with only voltages in the 13.8 range.

[pnichols]

IMHO, your switched "turbo mod" approach is the best way to use Sal's mod. Please make sure that the routing of the bell wire (sense line) is protected and ruggedized so that the wire can never get severed or can never come lose from the battery's terminals.

I would have preferred use of Parallax's "T" model to achieve about the same results. When I had my original 7345 replaced under warranty I requested their 7345T model and offered to pay the $$ difference, but my RV dealer would not do the exchange that way under warranty.

[Cstoliker]

I'll do the mod to be turn on and of with a swich. Call it "turbo" button.

[pnichols]

Sal,

Hmmmm....

1) Your sensing line mod will set the 7345's Vout value in accordance with the diode and summing point configuration behind the error op amp.

2) Your sensing line mod will hold the voltage on the battery terminals to Vout.

3) Your sensing line serves to force Vout on the battery terminals all the way up to 45 amps coming out of the 7345.

4) Your mod will do 3), above, regardless of the awg size of the main cable between the 7345 and the batteries. It will do this until failure of the cable if one was to use an unfused cable that just happens to be too small to carry 45 amps for long periods without over-heating.

5) Even though 8 awg cabling will of course carry 45 amps, some folks may try your mod using existing RV cabling smaller than 8 awg and think everything is OK. Hence my warning concerning use of your mod with small awg cabling that is not fused to the maximum that the cable can carry over time if that maximum is less than 45 amps - regardless of internal 45 amp fusing inside the 7345.

I'm not aware of any accusations or bellyaching. You did your mod to eliminate line losses between a 7345 and batteries it's charging ... plus (I think - per your 2009 explanations) raise the fixed output of a 7345 to higher than 13.8 volts.

For my AGM battery situation I don't want higher than 13.8 volts coming from my fixed voltage converter and I don't want to mess around modifying anything. I merely want a 7345, as delivered, to hold close to 13.8 volts on it's terminals all the way up to 45 amps ... as it's advertised performance curves says it will approximately do. I'll take care of voltage drop in the lines between it and the batteries - and I believe I've already stated earlier that I'll take the responsibility for doing this. BTW, this is easy to do safely because, as I've already stated, a 7345's terminals are big enough for up to about 2 awg cables and loss with 45 amps through 2 awg cables would be acceptably small for my needs.

In the final analysis, your mod is a great hobby project to demonstrate getting around a product's deficiencies. In the long run, I'll probably do what MEX and BFL13 do - use an inexpensive high voltage charger in parrallel with a 7345 to up the current a bit when charging my AGM batteries, as they charge so fast anyway even with only voltages in the 13.8 range.

BTW, thanks again for the quick math analysis you did in 2009 showing how low the internal resistance really was on the somewhat unusual Interstate wheelchair batteries I'm using!

[Cstoliker]

Thanks salvo, I'll look into doing the mod once I get it working correctly. Gotta replace those thee caps yet.

[Salvo]

Not correct at all. The new 1N4148 diode clamps output voltage. If cable resistance is high, then current is limited to less than max.

Instead of making wild accusations, why don't you do some analysis first, as I suggested before. The whole charging system is probably protected by a fuse already. The size of that fuse is usually sized to protect the cable we're talking about.

You keep bellyaching about voltage sag in your converter. Make the mod and you'll have no more sag. You'll see a 70% performance gain.

Sal

pnichols wrote:

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.

[pnichols]

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).

[Salvo]

Here's the mod to speed up charging by attaching a voltage sense line at the battery. The mod increased charging speed by 70% (in 2 hour period).

The mod is quite simple to implement and shouldn't take more than 15 min to make the pwb changes.



Sal

[pnichols]

I'm pretty certain my 7345 is acting properly. It's been the same since the day it was new.

One of these days, I'll load the RV batttery bank with a 30 amp draw from my PSW inverter and then turn on the converter to see: 1) If the 7345 supplies the 30 amps (as indicated by the battery bank's ammeter), and 2) how close the converter holds it's terminal voltage to 13.8 volts while supplying this current (of course I'll measure the 7345's voltage right on it's output terminals).

[Cstoliker]

We will see in a few days. Thanks again,

[KJINTF]

pnichols

I would hope to see after the repairs the unit is as good as it was new
Fixed many many of them and never had a recall / return / failure
Actualy have four of five of them in service here at the house/shops because folks wanted to toss them in the trash. You might want to take a look see inside yours - I suspect one or more caps are going south in yours


Cstoliker
Please make sure you use QUALITY caps Panasonic is one of the best however there are other quality manufacturers as well - also make sure they are rated at 105C not the 85C that were supplied at the factory

[Cstoliker]

MEXICOWANDERER wrote:
CHEAPNESS

MEET THE KING!

ME!


I wasn't joking nor was I sarcastic when I recommended the Harbor Freight 10-amp charger. It will add 18 amps charge rate when the batteries are low. Try that with any other $29.99 on the market.

I already have a 15amp charger, but the PWM 7345 would likly detect the voltage increase at the battery and likly reduce it's output. Don't think both could be used at once.

[Cstoliker]

Will do, my electronics supplier is not open week ends so it will be next week.

[pnichols]

Chad,

I'm very curious as to how your converter performs after you fire it up. If you get a chance, please let is know how it's output reads with various loads on it.

[Cstoliker]

I got it. It was topside +. Resistors look ok, they look as though they been replaced at some point in the past buy a repair facility that employs drunk moneys judgeing buy the soldering :-)...ugly but still functional.
All three if the caps you mentiond show slight signs of bulging on top. (Hydrogen buildup) GOOD CALL. I'll replace all three.

Thanks so much.