Watts, Amps, Volts, Ohms ?

[Mr Magoo]

Here's a thorny problem I'm currently working on and could really do with some advice!...

I have a 7ft box trailer - it's use it to transport a large 'stop me and buy one' ice cream bike that weighs around 90-100kgs. Getting the bike in and out up a ramp manually is quite hard so I've fitted a 1HP electric winch in the back of the trailer to help me, just like this one...

12V, 2000Lbs Electric Reversible Winch with 1.0HP motor on eBay (end time 31-May-10 16:24:53 BST)

The winch works fine with a 15Ah Silverline Power Station - just connect up the positive and negative cables and away I go (if a little noisy!)...however the winch is operated by a remote control switch and I need to extend the length of the cables running from the switch to the winch so I can stand outside as the bike is pulled up the ramp. I've bought 3m of 2 core 12V cable from my local Chandlers that is rated at 29A. There are no markings on the cable to indicate the cross-sectional area, but each core measures approx. 2mm in diameter and is similar (if a fraction smaller) to the existing cable running from the switch to the winch.

As I understand it, as Amps = Power/Volts, and the winch is 1hp (which is around 750W) so Amps = 750W/12V = 62.5 amps. However, the winch is rated to pull a maximum of 900kg, clearly far more than the weight of my bike. My question is this - is the amperage proportional to the amount of work being done...as the bike weighs around 10% of the winch's capacity, am I safe to assume that the amperage will also be around 10% (say 6-7amps)? If so, am I therefore safe to use this new cable I've purchased to extend the existing remote switch?!

Any advice will be gratefully received!!!

[Curmudgeon]

There is an old joke about how many WASPs it takes to change a light bulb. The answer is two: one to mix the martinis and another to call the electrician.

After reading through this thread, I know exactly how those WASPs felt.

[perchance]

You are best to size the wire to the full load rating of the winch.If you accidentally stall the winch you will let the smoke out of the wire. You should also install a fuse or breaker to protect the winch.

[Mr Magoo]

Originally Posted by Curmudgeon

There is an old joke about how many WASPs it takes to change a light bulb. The answer is two: one to mix the martinis and another to call the electrician.

After reading through this thread, I know exactly how those WASPs felt.

I've no idea what this means!

[Curmudgeon]

Try googling the term "WASP joke." In the U.S., WASP is an acronym for white anglo saxon protestant, a group that is stereotyped as wealthy and reserved.

What I meant is that all of these electrical terms make my head spin. If the problem involves ohms, amps, watts or joules I'd rather pay someone else to solve it for me.

[skipmac]

Originally Posted by GordMay

I’ve never been enamoured of necessarily imprecise analogies for mathematically exact electrical relationships.

Agree 100% when it comes to real applications but I do find the water analogy very handy to help non electricians begin understanding the basic concepts of voltage, amperage and resistance. Then hit'em with Ohm's law. Got to walk before you can run.

Post #1 by the way is a great article. With permission from the copywriter I'll print it out and keep a copy in my maintenance logs.

Regards
SkipMac BSEE