Renewable Energy Questions/Discussion > Automation, Controls, Inverters, MPPT, etc
15a 24v chinese charger questions
birdhouse:
i bought a charger from ebay for my 24v bank. it was sent straight from hong kong, and i believe it is designed to be the power source for LED lighting. it has an incoming voltage switch to go from 115 or 230v. there's also an adjustment screw for DC voltage out and a thermostatically controlled fan on top of the all aluminum case.
for $35 USD shipped, it seemed to be the best bang for my buck to be able to manually charge my battery bank with a generator running while at the same time running the generator for other uses.
i've also got a morningstar TS-60 in diversion mode hooked to the bank for my wind turbine, so that "should" make this operation fairly foolproof. not that i'm too worried about it, as i've got flooded batteries, and 15A going into a ~450Ah bank can't do that much harm.
Oz mentioned switching out a resistor on the voltage adjustment screw (trim pot??) to increase the voltage being produced by the charger. i wired it all up and hooked a volt meter to it while unloaded, and turned the screw. i got reading from below 19V and maxed the screw at 28.3V. i thought that was pretty good! it would be nice to hit 31V if possible to be able to use this charger for equalization as well.
questions: if i've got this charger running at 28.3 and say hook it to my bank at 23.5, i presume this will clamp the charger down to the lower bank voltage, but will this hurt the charger?
anyone know how to mod this? (Oz?) to get 31VDC
thanks for any input!
adam
oztules:
Hi Adam,
Different board all together to the one in mine from 7 years ago.... but your looks a simpler design ( mine had double sided and was delicate from memory).... no matter (looks the same from the outside though... well the box is the same at least)
The VR1 is your voltage control. It is simply part of a voltage divider network. It will have a series resistor going to it, and even perhaps one going away from it. The trim pot is just used to give you a small change to the resistance of one side of the divider.
I edited this part because it was cryptic:
As a simple start get some resistors about 10 time the value of the original in circuit ones close to the trimmer, and carefully place them across the resistor on the board, noting any change in voltage. The 10 times will change the value of the board resistor by about 10%.
I chose to vary the original value by 10% (by adding 10 times the original in parallel), because it will not hurt anything, but will give you an indication of which ones are in series with the pot...
Thankyou Rossw ( see rossw notes below)
end edit
When you find the one that pushes the voltage up or down, you know your in the voltage sense area. If it goes down, then use 10% less resistor in it's place, and you will probably be able to sweep the voltage up to 30v... if it goes up same thing, but you can just piggyback it on the original.
Does that make sense?
The other way is to pull the thing out of the box, and then trace where the lines go to and from the pot. Then you will know exactly which resistor to fiddle with..
Generally they pull one side of the voltage divider to ground, and as the chip sees the divider voltage fall, it tries to compensate by changing the pulse width (wider pulse) this pushes the voltage back up so the divider voltage it sees is comparable to it's reference voltage (usually another divider from the vref pin on the pwm chip.).
This style of supply has current regulation of generally 2 types. The first is an error amplifier that behaves like the voltage system above. It just gets a read of the current (usually by a single wire shunt) and feeds this to the error amp2. It then decides if the current is within spec, or too much. If too much, it backs off the pulse width to keep it in spec. So it will be held to batt voltage ( error amp v1 will remain out of the picture until the voltage gets too high) and the error amp (current) will take control.
Which ever error amp needs to over ride the pulse width will. So it will use the over voltage one if there is no load, and will use the current one if current exceeds a set amount.
The second one will shut the thing down for either a set period when it will try again, or until the load is removed... third type sets an scr, and need to be powered down before restarting at all (computer power supplies do this one. .... till you rip it out)
I have found they design these things with a lot of head room, and you can push them pretty hard .... particularly if you rewind the transformer with a bigger core, and change the current settings. I have pushed over 400 watts out of 150 watt ones without problem this way.
but I'm evil ;)
..............oztules
rossw:
It would seem "likely" that the 1.2K (R41) and 1.5K (R40) are in series with the trimpot to limit its adjustment range.
Undoing the screws and checking where the tracks go on the board, from the trimpot (VR1) would confirm that pretty quickly.
If it is as I surmise, then whichever resistor is connected to the "high" end of the pot (ie, when it's adjusted to maximum voltage - logically the fully clockwise direction) could be slightly reduced to get you to 31V.
The least butchery way would be to tack a buffer resistor across it from the top. To reduce the 1.5K resistor a little (say, 10%), you could solder a 15K (brown, green, orange in the old 3-band resistors) across the 1K5 to reduce it to 1.363K.
Re-test your outputs and tweek the value if its not quite to your liking.
Edit: Damn, beaten by a minute. Yeah, what oz says.....
oztules:
Sorry Ross :)
One more thing..... DO NOT REVERSE THE BATTERY LEADS TO THESE THINGS..... it won't be nice (done that too.)
If you think there is any likelihood of you doing an oztules, and something stupid (an oztules), then place a big diode across the + and - terminals with the cathode on the + and the anode on the - and an inline fuse in series with your leads.
That way when you do the inevitable, the fuse will blow and no one will know ;D
................oztules
rossw:
--- Quote from: oztules on February 19, 2012, 04:26:17 pm ---As a simple start get some resistors about 10% of the ones close to the trimmer, and carefully place them across the resistor on the board, noting any change in voltage. The 10% I chose, because it will not hurt anything, but will give you an indication of which ones are in series with the pot...
--- End quote ---
Just a little clarification here. I know what oz meant... but the way he's written it could let out magic smoke....
When he says "Get some resistors about 10% of the ones"... he means "to CHANGE the combined value by 10%"
So if it's 1K, parallel 10K.
If it' 1.5K, parallel 15K
It's not perfect, but it's close.
The other thing - if you choose to solder them on, turn off and unplug the supply. If the iron is grounded (and it should be), bad things will probably happen if you touch a grounded iron to a live circuit. :)
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