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What? ONLY 50 amp rating? (a rant about current)

There are a number of things to understand about jumper cables and vehicle electrical systems and these are easily confused by going shopping...

I went to Canadian Tire the other day to pick up some garden supplies and decided to have a look at standard commercially available cable sets.  I can only tell you I was astounded by the array of different ratings. One set was rated at 1000amps!!! What are you going to start with 1000amps? Maybe some farm equipment? A tractor trailer? My buddy's stereo? Not to mention that you needed to be Arnold Schwarzenegger  to open the jaws! (I am 6'3" 250lbs and I had trouble opening them).

So, in the interest of fair play I looked at some more meager examples. I found cable sizes in 10,8,6,4, and 1/0 (that's the 1000 amp one). Since my cables are 8GA I compared it the an 8GA of theirs - rated for 300 amps?!?!  I thought to myself, what makes these cables capable of sustaining a 300 amp draw for any length of time? Then it came to me, they CAN"T. You see the answer is quite simple. There are different ways of measuring capacity: constant and surge. Constant means that the cables can sustain their specified rating indefinitely (based on no change in environment and maintenance). Surge means that the cables can only sustain their specified rating for a few seconds.

You may ask, so what? You only turn the key for a few seconds at a time anyways. This is true but, let's discuss first a fundamental fact about electrical equipment and that is they run more efficiently and effectively when they have sufficient power.  While barely sufficient power gives the appearance of functionality it does not men that the unit is working effectively. The resulting effect is, your vehicle doesn't have the current to crank over fast enough, generate a sufficient spark, compensate for the dead battery and run the remaining electrics that come on with the ignition. My point? Simple....if your cables are not capable of carrying current for any period of time they will inevitably heat up. Ok, so they heat up, why is that a problem? Again the answer is simple, heat is caused by resistance in the conductor to the draw of current placed on it and INCREASES as the resistance INCREASES and the heat INCREASES with the resistance, and so on, and so on...Are you seeing the pattern here? The end result, you hook your jumper cables up to start a disabled vehicle and you begin to turn the engine over as you are do this the available current decreases just as you need the current to persist to start the vehicle. But I digress....

Let's look at what current is capable of (I was thinking about this since one article I read says that a starter can draw several hundred amps upon startup)

bullet60 -150 amps will Arc Weld ?!?!?!
bullet20 amps will ruin a slipped screwdriver ;-)
bullet50 amps will activate a plating solution
bullet0.5 amps will stop your heart
bullet100 amps will supply the average house

So to say that a car requires SEVERAL HUNDRED AMPS to drive a starter start I find hard to believe when the lead to most starter motors is 10GA which by specification is limited to 30amps (constant).

It's been 18 years since I took electronics in college so I am going to have to research the correct way to determine the surge current to give you a better comparison  It has something to do with the curve rate in heat and resistance rise compared to current and time. In other words how high can you drive it for the required period of time before the heat and resistance makes it either ineffective or unsafe.

I admit I am not entirely knowledgeable about car starters. I plan on doing some serious research over the next few weeks on this issue so stay tuned. this article isn't finished yet...


Well, I spoke with a friend who is C.E.T. (Certified electronics technologist) and who works for a power company and his say is that the surge current is approximately 3 times the constant. I inquired to him the calculation for the actual surge rating and he says it's a long complicated equation that is easily manipulated?!?! Well, that sort of answers alot of questions.

This tells me that the ratings on alot of booster cables are quite artbitrary. That provided the cables SURVIVE the operation they are being touted for they can earn the rating...

One thing he did warn me about is DIESELS. The current required for starting a diesel engine is considerable (starter, glow plugs, fuel pump). He said he tried an 8 GA set on a diesel and just about melted the insulation off the handles. 

The two advantages that the CYCLEBOOST system has over standard cables are 1) construction,  every other cable set I have seen are only crimped, mine are crimped and soldered providing both a sound mechanical and electrical connection and 2) the set only uses clips at one end, the clips are the weak point on any jumper cable connection. This is susceptible to debris and corrosion on the terminals, how well you put the clips on. the angle that you mount them on resulting in the amount of surface contact you achieve when you put them on the terminals. The fact that one end of the CYCLEBOOST is bolted to the terminals means that at least one end has a stable connection.  Some booster cable clips have teeth for gripping the terminals it usually results in less surface contact. The smooth clips require you to pay attention to what you are doing but you achieve more surface contact on the terminals.

I hope my rant has given you some insight. The exercise certainly gives me pause to think how some products are rated for our consumption...

Andrew Wells



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