So, i bought this
HT-2008 SMD hot plate on ebay. It's a 400W plate with a 80mm x 80mm heating element which is set into a larger phenolic HLT plate.
I bought this because i like the design, a smaller work area with some protective plate around it where you can rest your hand while working - or at least not get 3rd degree burns right away when you accidentally touch it. The price is around 90 Euro, which is around $100 US or £77 GBP
It's chinese made and from the outside it looks to be pretty well made. There were however some scratches in both case and top plates fresh out of the box. Nevertheless I decided to open it before even connecing it to mains, and boy, that was a good idea.
The bottom is made of another phenolic plate. That opens right up by removing the feet and we have access to the guts.
Immediately, we see some serious issues. First of all,
there is no fuse whatsoever. The mains is a standard IEC plug and there is no filter. While this is mostly a resistive load, there will be a SMPS in that regulator, and I'm not sure that solid state relais will just switch on the zero passes, so that is not good.
All of the spade connectors are not insulated. That's bad, especially since
the metal case is not connected to ground. Funny enough, the heater plate
is, and that is probably the part you will be making an effort not to touch when this is in use.
The solid state relais is a Taiwan jobby by
Fotek, and it has an UL mark. It's mounted to the case with a rather roughly machined piece of aluminium. No thermal compound, at the rated 400W it's propbaly fine. Still going to apply some before remounting for good measure. Peculiar: The relais has a hole on the back that looks like someone accidentally hit it with a drill. Might be a hint at that these units might be second quality parts or even rejected.
I checked all screw terminals, some of them were not tightened correctly. Also, some of the unused terminals were loose, so the screw can get lost over time and make short-circuits in the unit.
The heating assembly is mounted on yet another yellow HLT plate, and here comes the shoddy work. They didn't bother cleaning it, it has saw dust all over it. The brass screws look like the have been cut with a dremel after screwing, and they didn't bother to fully remove the plastic protective film entitrely. That would undoubtely molten during first use.
The heater is made of a solid block of aluminium with two heating elements embedded inside that are held with a grub screw. There is some play between the plate and the heating elements, so heat transfer will be affected somewhat.
Well, first things first, i connected the case to earth and put heat shrink on the spade connectors. I have a combined filter/fuse IEC connector on order which i will be mounting soon.
While reassembling, I discovered a stamp on the backside of the bottom plate. Apart from ISO9001 it's all chinese. Google translate doesn't make any sense of it.
So, all assembled and time to fire it up. I was surprised to be able to set the desired temperature to 999°C. Given that aluminium
melts at 660°C, that's borderline stupid.
Wanting to see if it would actuallys go that high, I let it heat, but when it started smoking at 450°C displayed temperature, i aborted the test. The actual temperature is lower - see below. Now, the seller does state that there can be some smoke on first use due to residual oil burning. However, I did not feel like setting my lab on fire on a saturday night.
Magic Smoke
The overall heating seems to be quite uniform throughout the plate. The temperature was a good 100°C below what is set as target, but I'm not sure how accurate the FLIR camera is.
The unit is advertised with a 400W rating, but my power meter says 312,8 Watts peak.
The HLT plate surrounding the plate does get hot, i measured it at 74°C when running the plate at 350°C target temperature. However, the edges remained relatively cool.
Picking parts of a heated board worked well, so it can be used for SMD work. The last set temperature is stored.
To sum up its issues:
Safety:
- no mains fuse
- no thermal fuse
- no insulation on spade connectors
- case not grounded
- thermal setting not limited
Use:
- Temperature readout very inaccurate. Haven't found out yet if this can be calibrated.
Pro's:
- Well. It's cheap and the mechanical construction is okay.
All these issues can be fixed or accounted for by the user, but still, the total lack of safety in the design make this a unit to pass unless you are on a budget and are willing to adress the issues yourself.
I hope you found this useful, if you have any questions, go ahead.