If you put 2 of the diodes in the bridge in parallel by joining the AC terminals, that would increase the amp capacity?
It will also lower the forward voltage?

If so, then I would have to adjust the voltage down using the adjustable resistor and also replace the last stud diode on the plate with a bridge. I dont plan on doing that, this is just for info purposes.

 

The forward voltage would be unchanged. I do believe the current would share across the two diodes and thus help with heat dissipation. The sharing may not be equal, so I wouldn't count on truly doubling the capacity, but it should be better than NOT doing that.

Actually the forward drop will drop slightly because that ∆V depends weakly on current. Less current, less ∆V.

 

If you put 2 of the diodes in the bridge in parallel by joining the AC terminals, that would increase the amp capacity?
It will also lower the forward voltage?

.

Not by much - the "typical" Vf is about 0.7V, but they do have some dynamic resistance, Vf could be as high as 1.1V close to the maximum rated current.

I'm guessing the surviving diode was checked to make sure it wasn't a Schottky-barrier type - the Vf would probably be nearer 0.4V at full load for those.

 

I used my diode function on them with the DVM.
The bridges are 0.48 and 0.45 and the remaining stud diode is 0.43

The two diodes on a separate heat sink plate that are feeding off the transformer taps are reading 0.26

After soldering the bridges were hot, so I measured the forward voltage using the meter they were 0.38 , so they drop when they heat up.

IF the voltages charging the batts are remarkably uneven, I may replace all the bridges with 50 or 100 amp versions to help even them out. The volts might vary naturally according to battery condition? Or will all 3 banks just see the same voltage regardless?
I think it will differ a little depending on state of charge.

 

I used my diode function on them with the DVM.
The bridges are 0.48 and 0.45 and the remaining stud diode is 0.43

The two diodes on a separate heat sink plate that are feeding off the transformer taps are reading 0.26

After soldering the bridges were hot, so I measured the forward voltage using the meter they were 0.38 , so they drop when they heat up.

Either your DMM diode check function is way off, or those bridge modules are esoteric Schottky bridges - straight silicon diodes should be somewhere between 0.6 & 0.7V.

Although 0.26V is a reasonably expected Vf for a stud type Schottky barrier diode.

 

I have two meters with diode function and they both read about the same thing?
So I dont know about that, the meters reading off.
One Bridge came from RadioShack, the other is off Ebay. Got them years ago. The RS one might be 25 amps version, the Ebay one s 50 amps.

 

Ok, its cold here about 30*F. When diodes are cold the vfd changes.
I retrieved from outside from the cold and took a picture with 2 meters off 2 diodes on that same heatsink plate.
You can see they are reading .45 to .5, other than temp, I just dont know.

 

the variable 12 watt power resistor sensitivity is extreme, little ohm changes mean battery voltage changes a lot on the output.
It is hard to get the volts set to where I want at 13.7vdc.

Plus these tend to break according to Raritan and I believe it!

How about leaving the 400 ohm resistor as a resistor only.
Use a round 2 watt 500 ohm potentiometer in the wire from the transformer rectifier diodes going to the zener type diode 6.8v. Bypassing the adjustable resistor completely?

Is that '6.8 v z' device a zener diode? with a 6.8v cuttoff-on?

complete control board, power in at top
ground at bottom

I bought a pack of 10 of these off Ebay. They are rated 1/2 watt 500 ohms.
https://www.bourns.com/pdfs/3296.pdf

 

Another mod, how about replacing those 2 rectifier diodes with a 50 amp bridge?
Raritan did that on the 24 and 32 volt chargers.

Currently this

Use bridge like this here

 

the variable 12 watt power resistor sensitivity is extreme, little ohm changes mean battery voltage changes a lot on the output.
It is hard to get the volts set to where I want at 13.7vdc.

Plus these tend to break according to Raritan and I believe it!

How about leaving the 400 ohm resistor as a resistor only.
Use a round 2 watt 500 ohm potentiometer in the wire from the transformer rectifier diodes going to the zener type diode 6.8v. Bypassing the adjustable resistor completely?

You're right to be precise - 13.6V is about right for long term maintaining, you need at least 13.8V to recharge a discharged battery before you grow a beard. On one occasion I saw a car battery with a sticker; "Charge not to exceed 14.4V" - so those are the values I tend to stick to.

If you might find a variable zener quite handy; there's the TL431, just add 2 resistors to programme the voltage, the current range is 1 - 100mA - watch the safe operating area curve, Im pretty sure it can't do maximum current and maximum voltage both at the same time.

 

Setting the voltage is tough due to the coarseness of the wire wound resistor. I looked at with a magnifying lens and where the adjustable clamp sits, the wire windings are slightly discolored and also loose from the ceramic cylinder. Go figure, it's only 45 years old and likely been under constant usage.

The zener is I think a linear type regulator, when the rectified voltage from transformer goes too high, it conducts, turning on the transistor 2N525 which ultimately turns off the voltage for the batteries by breaking the ground circuit. Then when voltage falls off from transformer, it stops conducting turning off its attached transistor ultimately allowing current to flow (allowing the BIG SCR thermistor to conduct to ground completing the circuit.) There is another 2N525 in the circuit. I guess when voltage is on the little lead gate of the SCR thermistor (part #8), it stops conducting? Or is it the other way around?

So there is a varying DC voltage in the 12 volt model? (uses two power rectifiers and center tap on the transformer)

Is there a varying DC voltage in the 24 volt model? (uses bridge rectifier)

 

Schematic has a symbol error. 2N525 transistor is NPN, they draw the schematic as PNP, arrow is backwards.

I was trying to understand the working of the circuit and noticed that.
For the zener regulation, when dropping resistance from where the power comes in from the rectifier diodes going to the zener, the charger voltage increases.

When 12 vdc positive is put on the ignition shutdown diodes, the charger output goes to zero. Power is applied to the transistor base, wont that make the transistor turn on, and turn on the SCR thermistor?

It seems to me sort of like thse 2 controllers are at odds with each other.

Can someone look at this and tell me how that works?
It also looks like they have the collector and emitter reversed. Collector should be more positive compared to the emitter.
http://www.electronics-tutorials.ws/transistor/tran_2.html

I also found the '25 watt 15 ohm resistor' in parallel with the SCR thermistor reads 100 ohms on my meter and is not 25 watts, it is 2 watts in size.

 

yes, verified 15 ohm is actually a 100 ohm in the device, colors are BR, BL, BR, Gold = 100 ohms.
I mean 15 ohms would send a lot of power threw the banks with little chance of regulation.

I checked and the other resistors are correct. So I think I found they drew the arrows on the 2n525 and put one of the wrong resistor values and wattage.

The zener schematic matches whats in the machine for position. I dont want to tear it apart to verify the leg positions on the 2n525. All the other diodes are correct orientation.

It seems the ignition shutdown volts would turn it on not off, can someone please explain that to me?

 

They drew the symbols backwards for the ignition cutoff diodes. I just verified this with my diode test function. Now I guess it makes more sense how the circuit works. Part number 7.
Still dont fully understand how the ignition cutoff circuit works. But I think I understand the zener regulator better.

If you were to repair using part numbers you would likely be ok, but using their schematic would make you wonder whats going on. 50 years later, I wonder if anyone ever noticed, and now who knows, but these chargers are still around and sold on ebay.

I think the ignition cutoff diodes work by draining off the higher voltage coming from the rectified transformer voltage compared to the lower battery voltage, so current flows away from the second 2n525 not allowing it to turn on which keeps the charging turned off. So even if the zener turns on the first 2n525 it can not turn on the second 2n525. The boats ignition voltage is lower than the chargers internal voltage, so that makes some sense now. And turning on the ignition switch creates a circuit path from higher (charger) to lower (boat) back through the boat ignition system.
It is sort of back flow charging power into the boat's ignition wires when the ignition switch is turned on.

 

Confusion, this says it is PNP
http://www.radiomuseum.org/tubes/tube_2n525.html

This says it is NPN
http://alltransistors.com/transistor.php?transistor=4674

So what is it?
Ok, it is PNP. I find one website claims it is NPN, 2 sites claim it is PNP, so I will go with PNP in a TO5 package
http://pdf1.alldatasheet.com/datasheet-pdf/view/120636/ETC1/2N525.html

 

Ok, How about putting a minipot to feed the zener diode.
I drew 2 diagrams with the the zener connected at either end of the variable resistor using a 0-500 ohm minipot. I think the first one will work?
Which way should it go?

or this

 

I was able at the boat to get the resistor set so the charger puts out about 13.7 volts. It was difficult, movement of less then a millimeter was needed.
When I get the little blue mini pots, they have 25 turns end to end, so should be very easy to dial in the setting and can do that with it running.
My plan in a few months is to set the minipot to 182 ohms, drill some holes in the phenolic board to attach it. Unsolder the red wire off the adjustable resistor and attach to the minipot. Then connect the minipot to the rectified volt connection. that will give me a lot of resolution in adjustment. Since I wont be messing with that awful adjustable resistor setting, if what I do does not work out, it will be easy to put it back

I think I could also modify the charger to do that periodic equalizing charge maybe with a switch and some resistors. http://batteryuniversity.com/learn/article/equalizing_charge
Simply add in a resistor in parallel to the zener to bump it up, perhaps another minipot with a switch to bump the volts up 10% higher than normal. I think this thing is limited to mid 15 vdc max due to the transformer itself.

The advantage of a charger - converter on a boat is it can drive a lot of 12 vdc loads. Some smart chargers shut down and your running off the batteries with no charging. Read that about the Genius chargers.

 

If the pot is wired as in post #36 (either circuit), I don't see how it will offer a useful voltage-adjustment .
Shouldn't the diodes at '7' in post #36 be reversed? Presumably the intended circuit function is that the charger should switch to trickle mode when 'Ignition' or 'Shutdown' goes high?

 

Here's how I'd add the minipot:

 

Thanks, If what I try wont work, I will try your circuit.
I ordered the minipots off Ebay, got 10 of them very cheap.

The ignition switch goes on +12v on the ignition shutdown, turns off the charger, it really does turn off, charge meter goes to zero.
If when cranking volts drops below 9 or 10, then the charger is supposed to come on again to give a starting boost to a low battery.

I checked those diodes and they are reversed compared to all the other stud diodes, the meters digital diode forward voltage test confirmed that.

I dont know why my mod might not work, it all depends which side of the 400 ohm adjustable resistor the zener is working with?
Does the zener interact with both sides of the 400 ohm pot or only one side?
I understand some things but still not sure exactly how the zener is working in this circuit.

Your circuit shows more resistance to the zener? 330 ohms plus the minipot pot.

The current circuit works with the adjustable 400 ohm resistor with 183 ohms on one side (+ side coming from rectifier diodes) and 200 ohms on the other side. How does this zener circuit flow current work with the the PNP transistor?