Magswitch Technology MAGJIG95 On/Off Magnetic with 95 lb/43 kg of Vertical Holding Force Yellow

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I assembled one of the second pass 30A prototypes using different FET switches than the first pass -- substituting a Vishay SiSS28DN for the IRLHM620. The Vishay part claimed slightly lower RDSon (1.6mΩ vs. 1.8mΩ @ VGS = 4.5V) and a higher max VDS of 25V instead of 20V. I thought, erroneously, that the higher voltage rating might improve the survivability of input transients when batteries are plugged into the input. The addition of R1 between the input and the LDO solves the problem by eliminating the capacitor (C2) that caused the ringing so a higher voltage rated FET is not required to support 2S-4S LiPo batteries. There may be some users that want to locate the hall-effect sensor away from the main circuit board. I added pads to allow leads to be soldered instead of mounting the sensor on the board.

Edit 2020-02-02: BHarbour pointed out my laziness in his comment. The following is a bit of extra work to solidify the design.] Reducing the standby current: Those are 14AWG wires. I believe that 12AWG is the max size that the board will accommodate. 14AWG is rated at 34A for chassis wiring. If you think you will be averaging more than that, then the 12AWG is rated at 41A. It's all relative to power and heat -- use your discretion. Test Results: It’s a great magnet-science demo, but you’re probably not going to save money with assemblies like this. It's easier and less expensive to just buy an MJ-95 or MJ-150 and get on with it. My first thoughts were to add a snubber -- a series R and C across the inputs. This could be just a tantalum capacitor with an appropriate ESR value . The problem I found was that the capacitor had to be greater than 100µF and the series resistance (or ESR) around 100mΩ. I could not find a reasonable size ceramic 100µF capacitor with a 25-50V rating, or a tantalum with <500mΩ ESR. The solution for the snubber to work was to put 15x 10µF ceramic caps in parallel -- so I abandoned this idea in favor of adding resistance in series with the input.

This 3S battery had a much lower internal resistance and there is a bit more ring as a result (And there was quite a bit of wire length between the battery and the board). Even so, the peak is about 17V, which is not a problem for the switching regulator (which has a 20V abs. max. input voltage rating). Though it is doubtful that the board will survive a 4S LiPo battery. Load Tests:

The Zener + pass transistor approach is one that I considered an dropped. Most Zeners need a bit of current to get up into their knee region, where they're stable. After you add the resistor and another SOT NPN it's a larger solution. The LDO is certainly more expensive, but simple and reliable. Or it just could be my prejudices from a long time ago and things have changed now. The condition of the surface also matters. If it’s painted, the magnet is a tiny bit farther away from the steel, so you get less force. Have a rusty surface? Less force. Maybe your surface has an irregular shape; this might also affect the force. A perfect entré into the Magswitch Workholding System. Once you have this tool, get all the other great tool attachments and simply mount them to the base as needed. The MagPress is part of a family of welding, lifting and fabrication products, that reduce project cost to complete and days to deliver. Major shipyard customers say, “Using Magswitch tools helps us save over 20 hours every week of unproductive fitting and grinding just on one substructure!”This all looked pretty good. I decided to see what the input transient voltage waveform looked like for a couple of different battery types: Our Vertical Featherboard adds a dimension of dual plane workholding. For use with the Woodworking Starter Kit and the Pro Table Featherboard. In the Magswitch Workholding System, it mounts to the Reversible Featherboard Attachment, Universal Mounting Base and MagJigs, each sold separately. Pro Table Featherboard Every Magswitch product is proudly designed, developed, manufactured and tested by Magswitch to ISO 9001:2015 standards. Frequently Asked Questions What is Magswitch Shallow field?

Downtime is eliminated with Magswitch, unlike traditional steel lifting systems. With a 100% duty cycle, no more standing or waiting around. Cost Savings I decided to use a 4S battery and a 60A ESC to generate a current above 30A to test the circuit. When I connected a fully charged (16.8V) 4S LiPo to the input the circuit lets some of its magic smoke out. After all the cussing ended I was able to determine that the TPS70950 LDO had apparently latched up -- the current was enough to fuse the VIN lead open: With load current 35A, the voltage across the switch was 40mV (that's 1.1mΩ). Power dissipation is only 1.3W, which should not be a problem for a board even this small. I repeated the measurement with 20A load current and got 22mV across the switch, and the same switch resistance. No changes required. So here's the plan:

Low Current Switch Specs:

When you rotate the knob, you’re rotating the top diametrically magnetized disc magnet by 180°. Now the magnetic field flows from one magnet, through the steel wall and into the other magnet.

Magswitch MagJigs are a fixturing clamp that will easily secure your fixture into place. Rotate the knob to turn it on and off for magnetic hold force. With the Magjig, simply drill a hole in a fixture and place the MagJig in to use for downward pressure clamping.The change from the AH180 hall-effect sensor to the S-5716 sensor changes the way that the switch works. Previously, the switch would change state when the magnet was removed. Now... Read more » In what direction is a force pulling on the magnet? This also matters a great deal. You’re not going to be able to apply 150 lb of shear or sideways force against an MJ-150 and expect it not to move. This is true of all magnets. Don’t heat up Magswitch ® magnets. Like all neodymium magnets, high temperatures can partially demagnetize them. Avoid anything above 176°F (80°C).