Ksger soldering station running on battery power - Page 1
Forum section: electronics / general

author: BlackICE
author_rank: Regular Contributor
timestamp: January 13, 2021, 07:29:12 am
content: I modded my Ksger to run in battery power by adding a power port to rear in parallel to the SMPS's output. Using 2 of my Milwaukee M12 batteries ~24.6V in series it works great. The same performance as plugged into the wall. I tried only one M12 battery ~12.3V and it doesn't work well at all. It take a long time to heat up and the temp drops fast when soldering. Using my old 15 cell NiCad DeWalt Batteries ~19V it works OK. I little slower and lower powered but completely usable. I did noticed a large current draw upon connecting the power leads, somewhat welding the contacts a little. Not great is you make and break the connection many times. Probably due to charging caps used by the SMPS. Would it be a good idea to a NTC in series with the battery connection? It would limit the inrush current at the expense of wasting some power and lowering maximum output.If you do this mod, but be stupid like me. I looked at the polarity of the connectors and assumed both sides are the same. They are not and I wired and power the SMPS backwards for a few seconds. I was surprised that it still worked and nothing got fried.

author: thm_w
author_rank: Super Contributor
timestamp: January 13, 2021, 10:21:14 pm
content: I don't see an NTC working very well.Few ideas:- use a single 12V battery and run a 24V boost converter module off of it, with an enable input. Enable the supply only after connecting it.- put diode on output of internal power supply, then run the battery to that, so the internal capacitor will not charge up- add in an active inrush limiting circuit (mosfet, or dedicated IC)

author: BlackICE
author_rank: Regular Contributor
timestamp: January 14, 2021, 02:53:44 am
content: Thank you for the suggestions. I think a schottky diode would work the best and be the simplest. I found a 3 amp schottky diode it would only drop 0.5 volts at 3 amps. What do you think using a 3 amp diode? Would that be pushing the limits? Using a multimeter I found the current only going up to 2.65 amps during startup. Under typical use the average current is much less.

author: thm_w
author_rank: Super Contributor
timestamp: January 14, 2021, 11:02:35 pm
content: Quote from: BlackICE on January 14, 2021, 02:53:44 amShould be OK.The lowest tip resistance I've seen is around 8 ohms, so you could hit 24V/8R = 3A peak. But as you said it seems to use a bit less than that under normal conditions.

author: DavidAlfa
author_rank: Super Contributor
timestamp: January 15, 2021, 01:57:01 pm
content: Can't you limit the max power in the menu?With T12 only 3amps are used, it shouldn't burn anything, unless the connection is very poor.Your drill will draw 5 to 10 times that when working hard. Get that connection better! 1.6m² wire should be enough.Are you using copper contacts in the batteries? Maybe the pressure is not enough causing a hot spot.

author: BlackICE
author_rank: Regular Contributor
timestamp: January 16, 2021, 01:06:59 am
content: The problem isn't the controller for the soldering iron, but the SMPS caps that I wired parallel to the batteries. The caps get charged as soon as the batteries are connected and act like a dead short. When I inserted the 1/4" male tab into the battery's connector I could feel it welding to the contacts.

author: DavidAlfa
author_rank: Super Contributor
timestamp: January 16, 2021, 06:59:12 am
content: But what capacity you put there? To suppress the initial rush you can put an inductor.

author: ledtester
author_rank: Super Contributor
timestamp: January 16, 2021, 07:45:42 am
content: I guess another option would be inserting a DPDT switch to disconnect the cap when you switch over to battery power.

author: BlackICE
author_rank: Regular Contributor
timestamp: January 16, 2021, 10:31:35 am
content: Someone else on the web did the mod with a switch. The switch has the added benefit of protecting from using the batteries at the same time that it is plugged into mains power. However I already drilled the hole for the power port in the middle, so not space left for a switch. An inductor would work but may create issues when the power is cycled on and off to power the heating coil. Diode is cheap, easy to install at the cost of a lost of max power and efficiency of 4% when on mains power.

author: DavidAlfa
author_rank: Super Contributor
timestamp: January 16, 2021, 01:18:39 pm
content: I wouldn't if there are capacitorsWhat's the problem then? The initial surge or running both from mains and battery?Use a nice 40v 10A schottky diode and you're done.Even better, you could put a p-mosfet there and a small signal transistor that disables it if there's power from the main power supply(Edit: For 3amps...not worth the hassle!)

author: BlackICE
author_rank: Regular Contributor
timestamp: January 17, 2021, 06:10:08 am
content: The surge is much more than 3 amps and only comes into play when the battery power is first connected. Using line power there isn't any issue with a surge, no contacts to weld and current is limited by the SMPS transformer. The 18650 batteries in the M12 pack can put out a lot of amps into an empty cap. A 3 amp diode would remove the caps from the circuit when on battery power at the expense of having a voltage drop when on line power. 1 part and 2 solder connections seen to be a good trade off for a wee bit lost of power.