Modification of the JBC HD-2A/B soldering station to work with 24V and 48V tips

[tru3533]

Browsing on the forum looking for modifications on how other JBC owners had modified the Heavy duty JBC HDA HDB HDC soldering station
I came across the post from URI https://www.eevblog.com/forum/reviews/modification-of-the-jbc-hd-2b-soldering-station-to-work-with-24v-and-48v-tips/msg3551961/#msg3551961

As I was going to modify my HD-2A, I decided to document what I did

JBC HD-2A with T250MA handle, tip C470 ready for modification



Transformer on these models are the same



Wires on the transformer we are going to modify are marked 10, 11, 12, 13, on the pcb. Start with desoldering wire 12 from pcb



No wire to be soldered to 12 on the pcb. No 12 is soldered to wire from transformer



Transformer winding's needs to be in series or parallel



Solder wires as shown, I use 0.5mm



Don't forget proper marking 



Finished, now I can use C245 tips.
DONT FLIP SWITCH WITH POWER ON, THIS CAN DAMAGE THE MOSFET

[thm_w]

So the station will not limit power right. If you have it set to 470 and insert a 245 tip... tip erupts in flames?
Maybe worth using this: https://mgispeedware.com/product/aircraft-switch-covers/

[tru3533]

JBC have been thinking about that.
Even with the station unmodified you can by accident insert a C245 tip.
So they added short circuit protection.

My only concern is operating the switch with load applied, this will introduce some nasty spikes 

Here you see what happends with 48V and tip c245 inserted

[tru3533]

Mariusgl11. What is unclear?
You see all wires in picture 5
I have added 4 white wires and one jumper on the switch

[tru3533]

You must remove wire 12 from pcb
scoateți firul de pe pcb 

[tru3533]

Dual 6A/125V works fine

[DavidAlfa]

Why the DPDT and cutting? Can't it be done much simpler?

[tooki]

Why the DPDT and cutting? Can't it be done much simpler?

The DPDT switches the two windings from series to parallel; both windings are always used.
Your suggestion doesn’t do the paralleling, so doesn’t have as much current capacity. (Whether the extra current is needed, I have no idea.)

[DavidAlfa]

The DPDT switches the two windings from series to parallel; both windings are always used.
Your suggestion doesn’t do the paralleling, so doesn’t have as much current capacity. (Whether the extra current is needed, I have no idea.)

I see. I'm not sure paralleling a transformer output like that is correct, unless they'were winded together, ex. like stranded wires.
Wouldn't any slight voltage difference cause the windings to fight each other and cause current flowing?
Maybe not that critical (don't want to think like these old grunts) , a transformer output quickly voltage normalizes with any small load...

The C470 has 7ohms, takes 7Amps @ 48V.
C245 would take about 10amps peak at 24V, but would heat so fast that I doubt it could cause any overheating issues.
But yeah, free extra current for anything

[DavidAlfa]

Nope, sorry, I have no JBC 

[tooki]

The DPDT switches the two windings from series to parallel; both windings are always used.
Your suggestion doesn’t do the paralleling, so doesn’t have as much current capacity. (Whether the extra current is needed, I have no idea.)

I see. I'm not sure paralleling a transformer output like that is correct, unless they'were winded together, ex. like stranded wires.
Wouldn't any slight voltage difference cause the windings to fight each other and cause current flowing?
Maybe not that critical (don't want to think like these old grunts) , a transformer output quickly voltage normalizes with any small load...

Putting multiple windings in parallel for extra current is extremely common. You see it on secondaries, but also on primaries (using the same series-or-parallel arrangement to allow use with multiple mains voltages).

I’ll be honest and say that I don’t understand magnetism all that well (I need to review it before final exams next year…), but I don’t think parallel transformer secondaries behave like parallel diodes.

Since output voltage is determined by the turns ratio, multiple secondaries (of the same voltage) will have the same number of turns, so the output should be identical. I doubt there’s as much variation as in some other types of components.

[CristianTM]

Hi !

Can tell me somebody what value have these two resistors ?
And the circle red points are linked together or not ?

Thanks.

CristianTM.