I want to be able to make device to track the movement of a trailer.

The problem is that most trailers don't have 12 or 24 V power, even when on the move.

The average amount of power that I need depends on how much time the GPS and the phone are turned on. I can work with 20 mA at 3.8 V.

If I have a large pack of Lithium Thionyl Chloride batteries I can get maybe a year or two out of them.

Is it possible to generate enough power from the trailer movement, in the same way that an automatic watch generates power as the wearer moves?

I was thinking of an eccentric weight on a vertical axis generator. My initial calculations make me think that only tiny amounts of power would be available, but I would welcome any comments from anyone who has any experience of this.

 

I'm assuming you are talking about a semi-truck trailer. ? Any chance of coupling a small generator to an axle?

Some early airplanes, without electrical systems tied to the engine, had a small wind turbine/generator on the outside of the fuselage, to charge a battery for the radio.

Ken

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It is for both semi-trailers and full trailers.

I realise that there is ample power available from the axles. However, it would make it very difficult for the unit to be hidden, and it would make fitting it a lot more tricky.

I had considered propeller driven generator would work, but makes it almost impossible to hide the tracking device.

(Modern jets still have a propeller driven generator and hydraulic pump, but it is only used when the turbines aren't running. Ram air turbine - Wikipedia, the free encyclopedia)

 

Two Canadian passenger jets glided very far to successful landings when they ran out of fuel. One flew sideways to slow down just before landing. Amazing.

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No tail or signal lights ?

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The problem is that stop lights may only be on briefly, and tail lights only on at night.

A trailer being towed in the day, out of town where there is no braking, will not have any power on it.

 

Trailers with no power for brake lights or turn signals should all be stolen then trashed.
They should not be on public roads.

I forgot. The power comes from the truck, not from the trailer.

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I assume this is so if the mafia steals the trailer, you'll be able to track it? Would a small solar panel on the roof, to charge the batteries, be too obvious?

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A lot of trailers don't have a roof.

http://www.blstik.com.au/images/Picture%20014.jpg

 

Ok, I thought you were talking about a tractor trailer. I think the best method would be to attach magnets to the axle and make a crude alternator with a coil mounted above it. You could enclose the magnets in two red colored plastic C type halves so it just looks like a join on the axle. Where would the GPS and cell antenna go on this thing?

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--- The days of the digital watch are numbered. ---

 

Have you seen the Zoomback?

Zoombak Personal GPS Locators ×€ Portable GPS Tracker ×€ Vehicle Tracking ×€ Family Car Monitoring ×€ Dog & Pet Finder

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There are two real problems with having a roll-your-own alternator. One is that a lot of trailers don't have axles that rotate. Often it is only the hub, wheel and brake drum that rotates. There is no drive to the wheels, so there is no need for an axle to turn.

The other problem is the suspension travel. That would alter the magnet to coil distance a lot. It would also make the fitting very difficult.

The GPS and cell antennas can be inside the box as long as it is plastic. Both will work fine under a chassis.

Yes, they are a competitor of ours. They seem to be having trouble of their own:- Zoombak Personal GPS Locators ×€ Portable GPS Tracker ×€ Vehicle Tracking ×€ Family Car Monitoring ×€ Dog & Pet Finder. The UK website of Zoomback has this to say:-
Global economic crisis forces Zoombak LLC to close down its UK consumer business