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So I want to buy an Anderson plug to install on my car in case I need to give someone a jump. Some of them say 300 amps and some say they are 50. The confusion is tow trucks have these. If cars and trucks need 600 to 1000 amps, why don't the Anderson plugs fry?

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    Have you asked Anderson? – CharlieRB Jan 12 '17 at 15:17
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    Not sure why there are votes to close. This is specifically about the workings of a connector used in automotive applications. Seems on topic to me. – cdunn Jan 12 '17 at 17:59
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Anderson supplies a whole range of connectors with varying current ratings.

Also, current ratings tend to be conservative: these are steady-state ratings. So a 50-amp connector can handle 50 A all day without overheating. That connector can handle more power for a short while. Similarly, jump leads are often far thinner than you'd expect because they only need to be able to handle 500 A for 10 seconds.

  • Jump leads can also be thinner because they are very short, and the voltage drop is less problematic for such short cables. – J... Jan 13 '17 at 12:08
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The Anderson plug will handle the Amps if selected properly. Paulster and Hobbes have stated this. I know that the Anderson plug is good for its stated cont rating because I do a lot of work for the CHCH R&D Branch of Forklift Rectifier Design and Build Factory.

There is one thing to watch out for and that is HOT DISCONNECT. If you pull out an Anderson connector when there is significant current flowing you will get a big spark. If you were to pull your proposed Anderson connector after you have the car started there could be say 50 Amps still flowing into the flat battery from the Donor Car whose engine is still running. If this proposed system is to be used by people who know what they are doing then that's OK. When the plugs arc under hot disconnect they become very hard to reinsert. (Even for a big guy that can lift people out of wheelchairs.) When the plug gets arced like this you have to pull the plug to bits and file away the little molten balls of metal. This may need to be repeated several times so the plug is easy for others to use.

To summarise this the Anderson connector is suitable for cold switching. Most large DC chargers from reputable manufacturers cold switch so they don't wear out the plugs.

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Tow trucks use Anderson SB series connectors, typically the larger SB350, gray to connote 12V DC. Look up the current ratings for that beast. Note the listed hot-plug amperage, so yes, yanking it hot is fine.

A starter motor is a series-wound DC motor, and locked-rotor amperage is quite large. Once the starter motor starts spinning in earnest, its current draw rolls back considerably and voltage comes up, so cranking power is not necessarily diminished.

To clear up a misconception, wire is not a fuse, and it absolutely can, and will, carry overcurrent to its own destruction. Resistance of wire is proportional to its length. A kilometer of 12 AWG cannot carry 1000 amps because its resistance is too high. But a short piece has a resistance very near zero. It will quickly (not instantly) overheat, anneal and melt. Put this inside glass and it is a fuse.

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There are two things to remember when jumping a vehicle:

  • First - When jumping a vehicle, the leads will only provide as much juice as they can provide. As long as you've hooked up jumper cables correctly (not putting them on backwards), you'll only pass as much current as the cables will allow, nothing more. This is the reason we are able to use booster cables to provide electricity to a dead or weakened battery and get it to work. You have to let it sit for a while to allow the juice to recharge the battery in order to work, because if you try right off all you will get is clicking or very little response. Heavier gauge cables will allow you to jump the disabled vehicle much faster because they can transmit more juice right off the bat.
  • Second - You may not need the full amperage of what the car needs to get it started. Many times a battery is weakened and may only provide half of what the battery is rated for and thus not allow the vehicle to start. If the vehicle needs 600A to start and the battery is only providing 300A, all you need is an additional 300A to bring the vehicle to life. (Please note, I'm just throwing amperage numbers out there as an example).

In either case, you won't override the amount of amperage the Anderson plug will provide. If you want to install one to help other people, it should not be an issue.

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    Uh, no. If you use a 50A plug to connect a running vehicle with a healthy battery to a dead vehicle, the current will be vastly more than 50A. The cable won't limit the current meaningfully either, its resistance is much too low for that. Too-thin jumper cables will happily conduct hundreds of Amps while the insulation is melting off from the heat. – Hobbes Jan 12 '17 at 18:25
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    How would a connector or cable limit the current it carries? There is only one way to do that: through resistance, Ohm's Law. The resistance of a cable is incredibly low, and not enough to keep the cable safe. I've seen this happen: I used inferior jumper cables (10 mm2) to start a car, when I disconnected the cables I saw molten insulation dripping from the overheated cable. In normal situations, a fuse is used to protect the cable, but a jump start requires so much power that a fuse is not feasible. so we accept a potentially dangerous situation and we mitigate it using thick jumper cables. – Hobbes Jan 12 '17 at 19:31
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    When you jump a car, the current is limited by two things: the remaining voltage in the dead battery (if this battery were full, there'd be no current across the cable), and the resistance of the starter plus dead battery. Both have very little internal resistance, in order to work: the starter needs to draw a few hundred amps at only 12V, and the battery needs to be able to supply that and it can't if internal resistance is high. So you're almost creating a short-circuit when you jump-start a car. – Hobbes Jan 12 '17 at 19:34
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    I think @Pᴀᴜʟsᴛᴇʀ2 is basically right, but for the wrong reason. The highest resistance in a cheap jump lead is often the wimpy connectors at each end. If they only have a resistance of 0.1 ohms at each end of the cable, which is quite likely, you won't get more than 60 amps even if you short the battery to earth. The heat generated in the connection doesn't damage anything much, because the battery terminal is a chunky piece of metal to conduct the heat away and there is no insulation to melt. – alephzero Jan 12 '17 at 21:17
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    "you'll only pass as much current and amperage as the cables will allow, nothing more" Aside from "current and amperage" being redundant, this is dangerously wrong and misleading. – Andrew Medico Jan 12 '17 at 23:39
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I use the regular 45A PowerPoles specifically in your use case. The PowerPoles don’t fry because of three reasons:

  1. When you initially connect the two vehicle’s batteries together, you are creating parallel connection between the two cars so the “dead” battery starts charging immediately because the two batteries want to equalize their voltages. That is, current flows from the higher voltage battery (or running car’s alternator or both) into the lower voltage battery. The longer you leave the two batteries parallel connected before starting up the dead car’s engine, the more cumulative effect this equalization will have. Depending on the resistance, this current flow can be large initially -- possibly even dangerous if you don’t know the batteries or voltage involved -- but the current flow will decay quickly as the two voltages equalize to 0 volt difference or not enough voltage to overcome internal resistance.
  2. When you start the “dead” vehicle, both batteries from both cars supply the car’s electric starter motor with current. That is, both the previously dead battery and the power supplied to it via the Powerpole will see current draw. See (1) above where the “dead” battery can be much revived by equalization phenomenon. Therefore, the current flow through the PowerPole is actually shared with the revived battery thus reducing current through the PowerPole.
  3. Although the current for starting the engine can be upwards to 80A to 200A, it is only for about 1 second. Many connectors have "burst" ratings that allow for much larger current for a short period of time.

Anecdotal evidence: I’ve been using this PowerPole setup for years on my vehicles and to start friends and coworkers vehicles (see LiFePO4 battery described below). It has never failed to start a vehicle that actually had a dead battery problem. The PowerPole connectors and the wiring have zero wear and do not heat up after a successful jump. In fact, my two vehicles have permanently installed PowerPoles in them for jumping and for charging from a wall outlet. The PowerPoles are tapped directly off the car battery’s main terminal via crimped and soldered ring terminal cables. The leads are stored securely in the engine bay and one longer lead goes out to the front grille area where I can wall charge the vehicle without having to pop the vehicle’s hood.

An additional advantage of using a quick connector like a PowerPole on a vehicle: I always keep one $45 rechargeable HobbyKing Zippy 4-cell 4200mAh LiFePO4 battery in my glove compartment on each vehicle. Of course, this LiFePO4 has a 45A Powerpole lead on it! The 4-cell LiFePO4 battery has a nominal voltage of 13.2V and significant 30C output capability. This battery is what I actually use to start other vehicles and my own from a dead battery. I’ve never had to do a cumbersome vehicle-to-vehicle hook up yet but it’s possible through my Powerpole leads pre-installed in my engine bay I described above. Most people have been flabbergasted that this little battery (that fits easily in a glove compartment) with a small connector can start a huge engine -- but see the three reasons above for an explanation. When I jump start another person’s vehicle, I do have a spare alligator clip that has a short 16-gauge cable that terminates with Anderson pole connectors to plug into the LiFePO4 battery. Of course, with my vehicles, I can skip the alligator clips and plug the LiFePO4 directly into my vehicle’s pre-installed Anderson PowerPole leads (see above). I never leave home without this LiFePO4 battery.

To reinforce explanation (1) above, sometimes a dead battery is so substantially drained, the initial connection fails to start the engine. In that case, I’ve left my LiFePO4 connected to the dead battery for a minute or two longer to allow more equalization effect to accumulate. Until the point is reached where the dead battery has received just enough charge that the second attempt successfully will start the engine.

Background: I use Anderson Poles extensively in hobbies like RC and electric bikes which makes it very convenient to use on my vehicles as well. I have crimped 100+ Anderson PowerPole connectors for personal use over the years! The PowerPole’s hermaphroditic connection, reuseable housing and crimped connection are very useful features in many applications despite them being rated a bit lower in current handling over other connectors of the similar size. I have melted some PowerPole connectors at lower current values than their ratings in different scenarios.

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