I am sure by now we have all "seen on TV" this device that would heat up, solder on immediate contact then cool so fast you couldn't burn yourself with it and would average 700 soldered joints per 4 pack of AA batteries. Pretty high claims, which as it turns out are close enough to accurate provided you don't investigate further. Coldheat does not itself make any heat whatsoever. Instead it conducts (word choice intended) a current through whatever material it's work tip is brought into contact with. The material must allow electrical current to pass or nothing will happen. The tip is composed of highly fragile, parallel carbon rods separated by a non-contuctive heat resistant material. Press too hard trying to get the tip to "dig in" and you chip the tip making your job even harder, tips are currently $10. Once electrons flow, the material bridging the space between the two carbon rods essentially becomes a resistance heater. Carbon conducts heat poorly so, again, provided the tip is only in contact with the point of work for the second or two required to melt solder you can indeed touch it immediately afterward and it is merely warm. Again, provided you use the tool only, and exactly, as the manufacturer says it works as specified. Note my language choice.
I cannot in clear conscience give this product anything less than a thumbs down. This tool did not survive the first project I put it to.
The project: Replace 12 LEDs on a PCB in a battery operated desk light. The steps are simple: desolder the leads on a LED, remove and repeat, then solder in the 12 replacements, test and return to service.
- Desoldering braid would make the job much neater and easier.
- Coldheat is not intended to be used for the length of time to apply desoldering braid, nor can sufficient pressure be used without damaging the tip.
- The insulating material between the carbon halves melted on the fifth LED.
- The plastic material that houses the contacts began to soften and had to be reshaped while still malleable.
- The tip had to be reshaped (a minor hack) with emery cloth multiple times.
- The handle also became warm, because the batteries inside the handle became warm with use.
- Accidentally contacting both leads on an LED lit all the remaining LEDs in the circuit.
- Arcing between the tip and the work seemed too common to be comfortable around things like static sensitive ICs.
The hacks required to keep the tool operational to see the project done:
- Shaping the soft carbon tip: the stock bevel tip looks a lot like the graphite leads in a drafting compass to me, so I treated it as such. Worn and chipped is useless anyway and was quickly renewed in a few seconds on fine emery cloth. I also rounded some of the edges to prevent chipping. It still chipped and wore but it took longer. The insulating material in the center is harder and an air gap has to be maintained. I did not have the tools to do this available to me, I was just trying to stretch the life of the tip. Then it melted.
- Using the pen upside down so the pilot light was on top. Unfortunately it meant the red contact light was on the bottom, but I could see it illuminate by glancing into my palm and looking for the glow. Note this also placed the bevel in an upper position. It is not transferring heat, only current like motor brushes so contact just has to be maintained. After using the pen in both orientations it did not seem to effect operation in the slightest.
- Power failure not due to battery life. I was using 2600mAh NiMH cells which although getting warm after several uses still tested fine on the charger. (I have a multifunction charger with LCD display) Batteries getting warm tells me the tool is drawing plenty of current. On troubleshooting the pilot light and/or heating indicator would flash on while manipulating the power switch. On disassembly to investigate the power switch I found that was indeed the problem and perhaps the tool's Achilles heel. The power switch is a sub mini SPDT and on research for similar I found a Radio Shack repair part 275-007 which is a DPDT. It's rating is 6VDC .3A and this is a problem. I did in fact take the Coldheat's switch apart and verified the burned contacts and partially melted plastic. I can easily believe it to have a similar rating to the Radio Shack part, and if that is the case then it should at MAX have 300mA passing through it. The switch is located between one side of the battery box and one side of the tip. Soldering is in effect a full short of the battery pack and passing it through a switch with a rating a small fraction of the available power is ludicrous. I removed the switch, soldered (yes, I got out another soldering iron to fix the soldering iron . . .) the wire straight from the battery pack to the tip terminal, reinstalled the batteries and immediately test melted solder with it as before. I just no longer had a power switch and would have to remove the batteries to turn it off.
My Verdict: The Coldheat cordless soldering pen, while on paper beats out traditional soldering irons, is in reality of such excruciatingly limited usefulness that it has no place on any serious repairman's workbench. That said, it is still a highly efficient tool for exactly what it is designed for: infrequent light soldering. No review that I have read said anything about battery life, so to me and because of direct experience, this may be it's one Pro. Just moved your stereo and need to tin a speaker wires in the far corners of a room, OK. Need to R/R a part on a PCB, OK. Need to R/R a half dozen parts on a PCB or put together a small project kit, NO, get out your regular plug in soldering iron. Sorry Coldheat, you're a nifty gadget but you need to have certain key flaws redesigned.