Shmoocon 2012, 757 Labs and Harbor Freight
Last weekend was quite exciting, as a few members of 757 Labs built a project for Shmoocon. It was an audience feedback moose that took feedback via an internet website and visually (then audibly) responded. The eyes were BlinkM LEDs and the audio feedback was done by means of a Harbor Freight airhorn kit powered by ham radio power supplies.
Of course, being a con project, it was a bit last minute. Planning and software started much earlier, but it's just how things go. One huge last minute issue was when a relay failed. This relay was supplied with the Harbor Freight airhorn kit, and was used to switch the high current load of the compressor by means of the the microcontroller which was triggering the relay by means of a MOSFET.
After only a few tests the relay seemed to fail. One would guess the transistor failed, given that it's a 40 amp automotive relay. This failure, however, seemed to echo some online comments about the air horn kit.
Before heading to Radio Shack, I popped the top on one of the relays and low and behold, it's a lie. The 40 amp relay is really a fake case on a 5 amp relay. It was purposely made to look like it was a heavy duty 40 amp automotive relay, when it is not! I've heard about Chinese vendors doing this with capacitors, but never have witnessed it in real life. So here you have it, the 40 amp relay included with the Harbor Freight air horn kit is a lie.
The fix was ultimately to go to Radio Shack and pick up some replacement relays. A few taxicabs and a few Radio Shacks later relays that looked pretty similar to the Harbor Freight ones were in hand, but the Radio Shack ones weighed quite a bit more. We had 3 of the air horn kits, and sourced 3 replacement relays. The air horns draw at least 20 amps, so there is no way the supplied 5 amp relay (mocked up to look like a 40 amp relay) would last very long.
Relays before removal of cover. "40A" automotive relay
Relays after removal of cover. It's really a 5A PCB mount relay!
Unfortunately this delayed the airhorns until mid-day Saturday, as the Radio Shack nearby in the city closed early.
I wonder if Harbor Freight knows their supplier is lying to them?
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February 2nd, 2012 - 16:35
Please complain! Harbor Freight is usually very good about replacements when things fail, and they should be told if they’re selling faulty gear.
February 11th, 2012 - 18:17
Pobably they do know! I got a heatgun (the cheap black and red one) and the Low Power rectifier diode (single for halfwave) was a 3Amp. it’s a 1500W rated heating element so…. yeah. that blew up after probably about half an hour of runtime. had to find a 10A diode and replace it (any larger and the leads wouldn’t have even fit in the terminals)