zener diode with PNP regulator mod for battery charger

P.S. You are aware that with the 2 x 330 Ohm solution, you just place the one side of the 330 Ohm to the sliding part of the old sliding resistor and move the slider a little bit up. Or you could just not use the slider at all and cut the red wire and place the 2 x 330 Ohm resistors as suggested by that person to both sides of the old 400 Ohm sliding potmeter. Whatever you do, the trick lies in regulating the voltage level to the base/zenerdiode. Please leave the 15 Ohm resistor in it also, it does not matter that much to take it out or leave it in, if you use 2 x 330 Ohm. Bert

 

P.S. if you use a current regulation as suggested, should you turn the slider and the 500 Ohm potentiometer too low, you will blow your transistor and also your 500 Ohm potmeter, whatever will burn first out. I do not believe that the 40 year old transistor can handle 190 milli Ampere, nor your zener diode. as the power dissipation will be more than 1 watt under such circumstances. Bert

 

Yes, I can give that a go, I bolded the part I like. Eliminates the old pot.
I have lots of circuits floating in my head, seems a lot of ways to do this.

I showed him this circuit, with four 100 ohms in series. He said i will get 3.9V-9.8V adjustment on the zener.
If I dropped the lowest resistor to 50 ohm, it will be 2.6V-9.8V



And here was his original suggestion with the two 330 ohm resistors.


I think he said I could get rid of the 400 ohm pot in the circuit and it will still work?

By the way, this 400 ohm pot is one of this charger styles biggest weaknesses - defects and that is even mentioned in the manual that they easily break. Mine has not broken yet, but I think pople break these because once moved, they are very difficult to get back in spec. I imagine people have tried to adjust volt output and broken them and thrown away a decent charger, due to they have no expertise to help them figure it out. I saw one of these in the trash at the marina and for some reason passed on it. Likely because I already have to much junk! But would have been good for parts or fix.

 

Yes, you increase the current through the SCR more. Do you really need such a wide adjustment. I would stick to 400 or even go to 500 Ohm to compensate for the parallel resistance created by the 330 + 500 + 330 Ohm. But it depends totally over how many 100 Ohms you place the 330 + 500 + 330 Ohm , just over one, over 2 or over 3 or over all of them.



And here was his original suggestion with the two 330 ohm resistors.


I think he said I could get rid of the 400 ohm pot in the circuit and it will still work? [/QUOTE]
You change the resistance from 400 to > 1000 Ohm and the current flow to trigger the SCR. It may work, but you may also find that it becomes unstable. I don't have the details for the SCR. i.e. minimum holding current.

Any potmeter is a weak spot, dirt, corrosion, too often sliding etc. But it seems you selected a quality 500 Ohm potmeter. I would stick to the 400 Ohm. Bert

 

Sdowney, I see you have removed your overload/transformer safety switch protection, as per your original 1st thread schematic. I would not do that, except if it is damaged. Bert

 

Yes, that was a test sketch schematic.

Still waiting on the mini pots I ordered. So far the charger is working well as is. But I want to make it better. I dare not attempt to move the slider!

I noticed something of interest. There are 3 isolator diodes supplying 3 banks.
I have it setup for the boat batteries as starter, house, generator.
If I put a load on the house circuit, the charger jumps the voltage up only on the house bank to maybe 14.3 from 13.6. The other 2 banks stay at wherever they were say 13.4 to 13.6

Why-how does it do that? Somehow, it keeps the other banks low, so it is somewhat smart.

The other thing is well, these are meant to supply power to loads, it is a converter-charger, which is good. But I think what happens is turn on a house load, and the charger responds with more volts because it thinks the battery is needing a charge. Is that still how things work today with boat converter-chargers? If I were to run a constant 12 volt house load, I think the house bank battery would get a lot more charging than it needs to get. I was wondering if that is what happens to other people.

I have also thought of adding another isolator diode to make a fourth bank. Not sure why I would but it seems that would work. I wonder if you could smarten up the charger, say use the fourth bank to supply house loads, but if the demand is too great, kick in using some relay device, like an ACR, the house bank battery. But I do read in the manual, says, always have a battery, dont run the charger to a load without a battery. But when boat was on land, I had batteries out of boat and used charger to power 12 v loads and it worked ok. Maybe Raritan is concerned too much load on the charger with no battery when running house loads?

 

Bertku, here is the manual, I shared on google drive

https://drive.google.com/file/d/0B43EHHTTdLSfbVBCU3ZMODZyVTg/view?usp=sharing

here is the parts list