12vdc 10A Switching Over Current Protection - Page 1
Forum section: electronics / projects

author: K1JOS
author_rank: Regular Contributor
timestamp: November 05, 2014, 06:39:47 pm
content: I have a high torgue DC bidirectional motor turning 75 pounds of anntena mounted mast. On startup it can draw 10A and then settles down to 7-8A. Sometimes, the coax cables to the antenna can get snagged around the mast or ice on the antenna/mast may be too heavy and I want to protect the expensive motor from drawing to much current. The simple solution would be to just place a fuse in line to the motor but this is outdoors, remote and high up so I would prefer a self-maintaining solution. I also want to add a wireless PIC or Amtel controller to the project but the high current switch protection is primary. I read elsewhere on EEVBlog forum about MOSFET/HEXFET switching that has current sensing. However there are so many choices with subtle differences in specifications I am lost. I was looking at the LT Linear Dec 2005 App note 105 on their Current Sense Circuit Collection. They have an example using LT1910, a dedicated high side MOSFET driver with built in protection features. It provides shorted load protection but only rated to 6A. I searched their website but couldnt find one that was rated for my needs at 10A.Also I need to be able to reverse polarity for direction control. Do I need a MOSFET current sense driver or are their better ways of meeting my objective?

author: jstarr
author_rank: Regular Contributor
timestamp: November 05, 2014, 07:35:44 pm
content: Thanks but as I said it is situated remotely (few hundred feet from the house) and I don't want to go back and forth in the winter to flip a breaker. Yes the DC supply is in a weatherproof box at the base but I also don't want it powered all the time. My goal is also to have a wireless controller that will control power, direction of rotation and provide compass sensor heading. I would like to stick to a solid state switch with some sort of reversible current overload protection. Any other advice in that regard??

author: Monkeh
author_rank: Super Contributor
timestamp: November 05, 2014, 07:36:54 pm
content: How curious, why the twin accounts?You can get remotely operated breakers off the shelf:http://www.e-t-a.com/products/circuit_protection_devices/electronic_circuit_breakers_and_solid_state_remote_power_controllers_ssrpcs/electronic_circuit_breakers/p/esx10-tc-dc-12-v/Those ones are interesting in that they're current limiting as well.

author: Jeroen3
author_rank: Super Contributor
timestamp: November 05, 2014, 07:54:12 pm
content: Do you want current limit, or overcurrent protection?Overcurrent protection is easy, get an INA202 or similar on the DC entry point of the controller.If you prefer an isolated solution, which doesn't care much about the used DC voltage because of the isolation, you can get one of those Allegro hall-effect sensors.I would also suggest the use of a comparator and logic (maybe a watchdog) if you're using analog outputs, instead of relying on software to turn of the bridge if measured value gets too high (or low). This way, a software or device failure will make sure the dc bridge turns off.A fuse or breaker doesn't hurt to prevent fire if the dc bridge fails. You're putting it outside without supervision, outside isn't the most friendly place for electronics.

author: Seekonk
author_rank: Super Contributor
timestamp: November 05, 2014, 08:44:14 pm
content: Complex current decisions are something that could be handled easily by a controller like the uno for $8 clone. Think of a low side FET with a low ohm resistor in the source. Developing only a half volt would give enough bits for the A/D to make a decision about current including time delays to prevent false trips. Status can be sent back via TS232 or add a wireless option.

author: K1JOS
author_rank: Regular Contributor
timestamp: November 06, 2014, 01:06:35 am
content: thanks to all for the excellent advice. I am not sure if I need over current or current limits. The motor has two mechanical stops (each direction) and there are two clutch settings(one per direction) that are adjustable to allow it to slip so as not to burn out. I was told to set each clutch so that the current draw was no more than a a few amps over the normal operating range, peak draw at start should be no more than 10A with normal draw around 8A. If the mast motor gets mechanically hung up before hitting the mechanical stops (ice bindings, etc) I figure the clutch should work the same way. After looking at the gears and clutch I figure this has to be very temperature dependent with the greased gear array needing more current during real cold weather. So my idea was to add some electronic oversight that if the current draw exceeded the clutch adjusted current draw, the power would temporarily shut off. I guess I may be overthinking the whole operation but I also want to control the power, direction and get some sensor data (mounted on the antenna mast) back to my indoor control so adding this current protection seemed like the right thing to do.PS Re: Twin account - my son-in-law a few houses down is a ham radio nut like me and we both love to read EEVblog. I just forgot when I jumped on his PC that it auto logs in when you bring up the website. Considering all the test stuff he borrows from me it's the least he can let me take of his.

author: macboy
author_rank: Super Contributor
timestamp: November 06, 2014, 04:08:59 pm
content: Auto-reset (self-reset) circuit breaker? Available in 10A (or anything else) at any auto parts store for a few $. The ones I am thinking of look like:

author: K1JOS
author_rank: Regular Contributor
timestamp: November 07, 2014, 01:42:38 pm
content: Thanks Macboy thats perfect !