Author Topic: ZD-8915 (SS-331) conversion from 18V to 24V  (Read 462 times)

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Online cybermaus

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ZD-8915 (SS-331) conversion from 18V to 24V
« on: January 26, 2021, 09:47:45 pm »
Some 19 months ago, I bought a ZD-8915. In a local store even, but it is still China stuff.
And at first, I was very happy with it. Still am, despite what I am about to write, would buy again.

But I started to get small annoyances. Being:

- Very loud FAN. I thought it was broken.
   Like many others, I replaced the fan nearly instantly, but that did not work. Below I explain why.

- Power switch on the back
   Has been moved to the front a while back.

- Extremely slow heatup time. 10 minutes to 400C (which is really only 350C)
   Main mod for this post.

- Temp is off by about 50C (edit: now also fixed)

- Bad sleep mode. Handling does not keep it awake, I have to hit something with the gun

- I may eventually also add a delayed vacuum valve, as I have seen others also do.


So, it turns out the noisy fan and the slow heat-up time are related. The problem is, it has a 24V heating element, a 12V air pump, 12V Fan; But a 18V power supply.

So putting a 24V 90W heating element on 18V yields only 50W. And indeed, checking consumption that is what it takes.
That is the slow heating explained.
[attach=1]

Furthermore, the 18V is dropped with 2 ceramic 1R5W resistors to 12V for the airpump. Very wasteful.
BUT, the 12V cooler fan is on the same resistively dropped 12V rail as the Airpump. Ergo, it is nearly always running on 18V !!
Only when you run the pump does it drop to 12V, but I never noticed the fan sounded better when the pump was running. You know, with the added pump noise.
And when the pump does not run, then voltage barely drops, so the full 18V over the 12V fan.

Yeah, that will make it sound as if it is about to explode alright....


And finally, not very critical, but also a bit silly:
The control board is running from a 78L05, is again from the 18V, but again resistively dropped to 15V.
The resistivity dropper is inside the PSU even, so it needs two extra leads out of the PSU. Not sure why. Maybe the 78L05 gets to hot from 18V, but not from 15V?

The Mod:

I modded the PSU from 18V to 24V by tweaking the resistor network around the TL431AA voltage reference.
Adding a 68K resistor parallel to the R8 resistor (24K Ohm) yielded 23.5V output. Which is good enough, especially as the capacitors are only rated for 25V
[attach=2][attach=3]

Next I added a cheap DC/DC board to convert the 24V to 12V, and will now feed all 3: airpump, control board and fan, without any resistive dropping.
I did test if the board could handle a continues 2.5Amp for the Airpump. Not that the Airpump runs continuously, but to be sure...
[attach=4][attach=5]

From the PSU, I removed the thin 15V red/black leads for the control board (the resistive dropper for that was inside the PSU), as well as the 18V thin black/white leads for the airpump. And instead added proper (thicker) Red/Gray wires. The reason for the odd  Red/Gray color combo is that the original colors were also odd.
For example: two of the black wires of the PSU were +18V, and one black wire was GND.... Go figure the logic of that....
So anyway, as I did not want/need to change the Black/White wires to the Iron, I kept Black as +V, and chose different colors for permanent 12V and permanent 0V

Code: [Select]
original       new     meaning
Black (thick)  Black   +18V (now +24V) for Iron (unchanged)
White (thick)  White   PWM switched ground for Iron (unchanged)
Black (thin)   Red     +18V (now +12V) for Airpump/Fan (now also Control board)
White (thin)   Gray    permanent ground
Red (thin)     --      +15V for Control board (removed)
Black (thin)   --      ground for Control board (removed)
Orange (thin)  Orange opto-coupler to Switched Iron ground
Green (thin)   Green  opto-coupler to Switched Iron ground


The power distribution board also was slightly changed. Basically, I removed the two large resistors, and re-used their pads to create a +12V and 0V point for the control board wire. Not too hard, see the images.
[attach=6][attach=7]

Now the device heats up much faster, draws the listed 90W while doing so. And the Fan sounds more reasonable.
I may still changed the fan for an ultra-quiet one.

Mods I may make in the future

- Replace Fan by more quiet one, and add internal shroud for more logical airflow
   (but the airpump is noisy anyway, so maybe not)

- Tune the pots on the control board to see if I can make the temp readout better
   (did not touch them yet)
done

- Add small vacuum delay valve in the handle, so the suction comes in with more of an initial burst.
    Something like this: https://youtu.be/j8LMdIZuDyw but nicer looking)

- Put a relay for the AirPump, rather then running 3A over the tiny conductors and microswitch of the gun.

- Link the sleep/shake input to the trigger switch


Or not. After all, it is working, and I do not need to wait 10 minutes anymore every time I want to use it, so I may loose interest.
Anyway, let me know if you have suggestions, of if you thought this useful.

Have a nice day.

PS: if someone knows why my inline images are not working, please reply or even dm me.
« Last Edit: January 29, 2021, 10:32:02 pm by cybermaus »
 

Offline Andy Watson

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Re: ZD-915 (SS-331) conversion to 24V and other tweaks
« Reply #1 on: January 26, 2021, 10:16:33 pm »
There are some odd design choices in these units. I traced-out the circuit of my 331B version here:
https://www.eevblog.com/forum/testgear/using-a-proskit-ss-331h-on-110v/msg2283177/#msg2283177
It appears that all version use the ZD-P150 power supply module.
 
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Online cybermaus

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Re: ZD-915 (SS-331) conversion to 24V and other tweaks
« Reply #2 on: January 26, 2021, 10:35:06 pm »
Nice schematic. I did in fact already found that a few days ago, and used it, thanks.

So does your SS331 also have a 24V element, or is there a special/unusual 18V element in it's gun?


Edit: also, your schematic has a 6-pin connector, my device has a 7-pin one. And I cannot find any wire for the shake sensor in your schematic
Now, it was mentioned by the seller (local shop) my device was a new version with sleep. So likely that is why I have an extra pin.
I did not focus on that while it was open, and the device is closed and back in its place now.
But it does indeed have sleep and wake. Be it I have to give it a rather hard tap to wake it.

but thinking about it, having a new version, new handle, who knows, maybe I also have a different heat element. It would explain why I see no-one else complain about the slow heating.
« Last Edit: January 26, 2021, 10:54:40 pm by cybermaus »
 

Offline sam_sam_sam

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Re: ZD-8915 (SS-331) conversion from 18V to 24V
« Reply #3 on: February 19, 2021, 02:21:31 am »
cybermaus

I have several ZD-915 that do not have the sleep function on them so I do have that feature

But I have to ask you about the modification that you did to the switching  power supply

You know that it has a  +5 volt rail but did you know that it also has a -5 volt rail Zener diode with a 1 watt resistor how warm does this resistor get with the extra voltage to this device

How well does this modification work and how often do you use it  for hours at a time or a few times a week the reason I am asking is I might want to do this modification on mine but senses you have already done it I just wanting to know how well is holding up

How badly does the temperature over shoot or under shoot the set point
« Last Edit: February 19, 2021, 11:31:48 am by sam_sam_sam »
 

Offline mjongh

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Re: ZD-8915 (SS-331) conversion from 18V to 24V
« Reply #4 on: February 21, 2021, 02:15:00 am »
I have opened up my ZD-8915 to do this great mod.

It has a slightly newer version of the power supply (V4), which uses different values for the feedback circuit resistors.
In this version you need to add an 6K8 resistor parallel to R8 to end up at roughly 23.5V.
 

Online cybermaus

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Re: ZD-8915 (SS-331) conversion from 18V to 24V
« Reply #5 on: February 22, 2021, 09:29:44 pm »
Cool. Thanks for the feedback on the newer version.

It cursory looks like all your values (in this section) are divided by 10.
Maybe they done that to make it less susceptible to noise.
« Last Edit: February 23, 2021, 06:31:35 am by cybermaus »
 

Online cybermaus

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Re: ZD-8915 (SS-331) conversion from 18V to 24V
« Reply #6 on: February 22, 2021, 09:58:15 pm »
Sorry, I missed your questions. Not always checking every day.

cybermaus
You know that it has a  +5 volt rail but did you know that it also has a -5 volt rail Zener diode with a 1 watt resistor how warm does this resistor get with the extra voltage to this device
I am not aware of any -5V rail. Can you provide more details on that?

I do remember a input voltage divider, so the CPU knows the input voltage, probably as some sort of power-good signal. But I would not call that a rail.
In case you mean that one: It is now getting 12V instead of a varying 18V~15V, so any such resistor would get less hot.

How well does this modification work and how often do you use it  for hours at a time or a few times a week the reason I am asking is I might want to do this modification on mine but senses you have already done it I just wanting to know how well is holding up.
If I am honest, I use it sparingly.
When I do use it, I am happy to have it, but I am only an occasional hobbyist, and also nowadays more stuff is surface mount.
So if there is a 1W resistive dropper somewhere that I did not notice, and it is getting 24V instead of 18V, I may indeed not have noticed it breaking yet.
But as stated, I did not notice a -5V rail.

How badly does the temperature over shoot or under shoot the set point

Well, I have not done laboratory quality testing on that. Just a cursory check with my temp probe.

But when doing that, I noticed that even with the 24V, there is still a delay before the read-out temp reaches the tip.
I can already hear the regulator starting to modulate (you can hear the high pitch of the switched PSU), while the heat at the tip is still creeping up.
As a result, there is no real overshoot.

Undershoot usually happens because the gun goes to sleep while I am using it, which usually leads to me cursing and whacking the handle to my desk to wake it up.
But now at least it goes back up rather quickly.

The whole sleep shake sensor is rather silly. Unlike a normal soldering iron, this device has a usage trigger-switch.
The engineers messed up when they did not realise they could have used that instead of adding a shake sensor with wire and connector.

« Last Edit: February 22, 2021, 10:02:43 pm by cybermaus »
 

Online cybermaus

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Re: ZD-8915 (SS-331) conversion from 18V to 24V
« Reply #7 on: February 23, 2021, 03:32:48 pm »
[attach=1]Additional note after checking Andy Watson's schematic:

I still do not see your -5V rail anywhere.
And additionally, the new 24V goes nowhere except directly to the Iron. So it should not matter unless if inside the PSU itself


However/Indeed: I do now see inside the PSU a Diode/Resistor combi D1/R1 (not a Zener) at 360 Ohm / 2 Watt
That indeed would get 1.6W instead of 0.9W. Should be OK, but had I seen it while I was in there, I may have modded it.
But still 2W is more then 1.6W, so should be OK.


Then again, not even sure what this diode/resistor is supposed to do?
Provide some minimum load when the Iron is not driven, so the PSU does not over/undershoot every time the FET switches?
« Last Edit: February 23, 2021, 04:28:33 pm by cybermaus »
 

Offline sam_sam_sam

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Re: ZD-8915 (SS-331) conversion from 18V to 24V
« Reply #8 on: February 23, 2021, 04:32:30 pm »
This is a Zener diode setup and it is used for the controller board which when I saw this I thought it was a odd but I know this because I am going to run this until on 24 volt battery pack and when I tried to use this way the temperature part of the  controller would not work and you have to have this circuit for it this purpose

But you also have to use a SCR setup for a 3D bed table heaters and a PWM controller for this to work correctly I just have to use a computer battery pack module and reconfigure it for 24 volts and this project would be finished

The temperature over and under shooting is a lot better but you do give some speed to how fast ( the results are not bad ) it gets to the temperature that it is set to but on battery power you do not want the overshooting to be at a minimum to conserve battery power  because it runs at lower current

I have read that these Desoldering Gun have a life of about 500 hours but I seem to get more hours than this but when they get to about 1000 hours of use they have tendency to clog more often and the wire cloth covering turn black and when this happens you running hours left are very limited time for a new gun

One note about running it at 24 volts the heater element will not last as long because the more current it pulls and not a good option when running for hours and hours at a time I have thought about running this unit on an external switching  power supply before and might still do but I have a selector switch to switch from 12 volts to 24 volts for turbo boost but only use this when doing double sided circuit boards with wide ground planes but so far I have not found the right switching power supply for this purpose yet

One note that this is a failure but does not happen very often at least with my experience is temperature sensor failure and you will know that this happen because you will see — — for the temperature reading results but the heating element will still get power and destroy the heating element there is no fix for this failure as far as I know I have even tried to remove the temperature sensor wires from the gun but have not been successful in doing this
« Last Edit: February 23, 2021, 04:56:36 pm by sam_sam_sam »
 


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