# How do car batteries and inustrial battery chargers handle such high currents (amps)? **URL:** \ **Category:** Factual Questions\ **Created:** [January 21, 2020, 8:21pm UTC](https://boards.straightdope.com/t/how-do-car-batteries-and-inustrial-battery-chargers-handle-such-high-currents-amps/846769 "2020-01-21T20:21:50Z")\ **Posts on this page:** 13\ **Page:** 2
**Author:** ![48Willys](https://avatars.discourse-cdn.com/v4/letter/4/db5fbb/32.png) [@48Willys](https://boards.straightdope.com/u/48Willys)\ **Post date:** [January 23, 2020, 7:09am UTC](https://boards.straightdope.com/t/how-do-car-batteries-and-inustrial-battery-chargers-handle-such-high-currents-amps/846769/21 "2020-01-23T07:09:32Z")
Just to add to the confusion here, in many factories, the forklift chargers all have 3 phase 480 volt inputs. Being 480 volts means that the amperage required for them is smaller. Being 3 phase means that the amperage required for them is smaller still. This means that the wires needed for the input can be much smaller. The cables that attach the charger to the battery will still need to be fairly large. Keep in mind that most forklift batteries are at least 48 volts, many are in the 90 volt range. I can almost guaranty that each charger has its own circuit breaker on an electrical panel somewhere. I think that it is required in the national code. All of the ones that I have dealt with have been laid out that way. IHTH, 48. ---
**Author:** ![48Willys](https://avatars.discourse-cdn.com/v4/letter/4/db5fbb/32.png) [@48Willys](https://boards.straightdope.com/u/48Willys)\ **Post date:** [January 23, 2020, 7:17am UTC](https://boards.straightdope.com/t/how-do-car-batteries-and-inustrial-battery-chargers-handle-such-high-currents-amps/846769/22 "2020-01-23T07:17:06Z")
> [@RedSky](#): > > If you look the wall plug it’s nothing like your house, their running three phase power, each charger is plugged into 480 volts. IME, Most forklift chargers in a factory are hard wired, and do not have a plug for the input. Those chargers are bolted to the floor & are not going anywhere. Thus, no need for a plug. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [January 23, 2020, 7:30am UTC](https://boards.straightdope.com/t/how-do-car-batteries-and-inustrial-battery-chargers-handle-such-high-currents-amps/846769/23 "2020-01-23T07:30:13Z")
To determine the max current capability of a wire, you first have to look at two things: - Conductor material (usually copper) and plating material on conductor (e.g. no plating, tin, silver, nickel). - Type of insulation (e.g. PVC, silicone, PTFE, ETFE, or even no insulation). The conductor (along with the plating) has a max temperature rating, and the insulation has a max temperature rating. Whichever of the two is lower determines the max temperature spec of the wire. If, for example, the conductor was copper w/ silver plating (max temperature rating of 200 °C) and the insulation was PVC (max temperature rating of 150 °C), then the wire would have a max temperature spec of 150 °C. Once you know the max temperature spec of the wire, you can calculate max current based on the following: - Cross-sectional area of conductor. (This determines resistance per unit length. The smaller the area, the greater the resistance, the greater the power dissipation due to I²R, and thus the higher the temperature for a given current.) - Solid or stranded conductor. (AEBE, stranded can carry slightly more current vs. solid.) - Wire length (a very short wire can carry more current due to heatsink effects at end terminals). - Thickness of insulation. - Emissivity of insulation. - Orientation of wire. (AEBE, a horizontal wire can carry more current than a vertical wire.) - Whether or not the wire is “alone” or bundled with other wires (and how many are in the bundle, and how much current they’re carrying). - Temperature of ambient air. - Velocity of ambient air. - Thermal characteristics of sheath or conduit, if present. - If AC, frequency of the current (AEBE, resistance per unit length will increase as the frequency increases due to the skin effect, thereby raising its temperature.) - Time (1 ms? 1 s? 10 s? Continuous?). And that’s off the top of my head. I’m sure there are more variables. Of course, not all the variables are of equal importance. Some have a 1st order effect, while others are 2nd order, 3rd order, etc. Suffice to say, in order to calculate an accurate value for the max current spec of a wire, you need to take a lot of variables into account. A computer model is a must. AEBE = all else being equal ---
**Author:** ![Marvin\_the\_Martian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/marvin_the_martian/32/2898_2.png) [@Marvin\_the\_Martian](https://boards.straightdope.com/u/Marvin_the_Martian)\ **Post date:** [January 23, 2020, 4:31pm UTC](https://boards.straightdope.com/t/how-do-car-batteries-and-inustrial-battery-chargers-handle-such-high-currents-amps/846769/24 "2020-01-23T16:31:40Z")
> [@48Willys](#): > > No VW was ever positive ground. I used to be a VW mechanic at a dealership. The Beetles, (Type 1s), were all 6 volt up to 1966, in 1967 the Beetles came out with 12 volt electrical systems. The buses, (Type 2s), and the Square-backs, (Type 3s), all switched over to 12 volts at about the same time. Type 4s were always 12 volt systems. > > IME, VW drivers are still a pretty communal bunch, especially air cooled VW drivers / owners. > > I am not trying to argue here, I just do not want a reader to be misinformed. > > BTW, I found that replacing the 2 gauge factory battery cables with 00 gauge ones fixed many of the air cooled 6 volt electrical issues. So much so, that now when I repair any 6 volt systems, they end up with 00 gauge battery cables right away. > > IHTH, 48. Well, I was six or seven years old at the time so forgetting a few details isn’t too shocking. I think the Beetle was a 1963, so definitely 6 volt. The Microbus we got next was definitely 12 volt. Was the battery under the front hood? If so, a pretty long electrical run back to the starter so not surprising that upping the size of the battery cable helps, especially since a 6V system has less headroom for voltage drop. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [January 23, 2020, 7:00pm UTC](https://boards.straightdope.com/t/how-do-car-batteries-and-inustrial-battery-chargers-handle-such-high-currents-amps/846769/25 "2020-01-23T19:00:50Z")
> [@Dr.Strangelove](#): > > To expand on this a bit, ampacity charts [such as this one](https://www.powerstream.com/Wire_Size.htm) have separate columns for “chassis wiring” vs. “power transmission”. The chassis wiring current limits are several times that of power transmission. The power transmission ratings assume conductors which may be bundled together, have fairly strict temperature limits, and long lengths. Chassis wiring will be better ventilated and have shorter lengths, and can get away with higher currents. Cool, perfectly sensible portmanteau word, ampacity. Never knew it. Side question: conductors other than copper have different ampacities. Wouldn’t special-purpose applications, from semiconductors to solar arrays to massive batteries, have custom materials engineering? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [January 23, 2020, 7:06pm UTC](https://boards.straightdope.com/t/how-do-car-batteries-and-inustrial-battery-chargers-handle-such-high-currents-amps/846769/26 "2020-01-23T19:06:50Z")
> [@Leo\_Bloom](#): > > Cool, perfectly sensible portmanteau word, ampacity. Never knew it. > > Side question: conductors other than copper have different ampacities. Wouldn’t special-purpose applications, from semiconductors to solar arrays to massive batteries, have custom materials engineering? I’m not really sure what you mean, but many metals other than copper are used for conductors. Aluminum is used for transmission lines, because it is much cheaper and lighter than copper, and that makes up for it’s lower conductivity. Gold is used in IC bond wires (see\*\* Dr. Strangelove\*\*’s post above), as is aluminum. Indium Tin Oxide is used for solar cells. Superconductors are used in MRI machines, and Silver was used in the Manhattan Project for “Calutrons,” because Copper was scarce (Silver is probably ideal for this, but sort of pricy). ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [January 23, 2020, 7:14pm UTC](https://boards.straightdope.com/t/how-do-car-batteries-and-inustrial-battery-chargers-handle-such-high-currents-amps/846769/27 "2020-01-23T19:14:08Z")
I guess I was so impressed with the clarity of _that_ ampacity chart I was wondering about all the other ones out there. Superconductor amapacity chart. Huh. Actually, was sort of wondering if conductors other than copper would be useful/economically efficient to save space under the hood. Obviously not :). ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [January 23, 2020, 7:22pm UTC](https://boards.straightdope.com/t/how-do-car-batteries-and-inustrial-battery-chargers-handle-such-high-currents-amps/846769/28 "2020-01-23T19:22:20Z")
> [@Crafter\_Man](#): > > … > Once you know the max temperature spec of the wire, you can calculate max current based on the following:… > > - Orientation of wire. (AEBE, a horizontal wire can carry more current than a vertical wire.)… Holy crap, gravity limits the little suckers at this scale? ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [January 23, 2020, 9:11pm UTC](https://boards.straightdope.com/t/how-do-car-batteries-and-inustrial-battery-chargers-handle-such-high-currents-amps/846769/29 "2020-01-23T21:11:26Z")
> [@Leo\_Bloom](#): > > Actually, was sort of wondering if conductors other than copper would be useful/economically efficient to save space under the hood. Obviously not :). The wiring doesn’t take up much room under the hood in a normal car. However, electric cars benefit from improved conductivity. Because you need less material for the same conductivity, you can pack the electromagnet windings more closely, which makes them smaller, which means you can use even less material. So the motor weighs less and is more efficient, so the battery can be smaller, and so on. Copper is good but silver would be better, so it’s too bad it’s so expensive. Superconductors are a possibility but the cooling system weighs a lot and itself takes energy. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [January 24, 2020, 7:10am UTC](https://boards.straightdope.com/t/how-do-car-batteries-and-inustrial-battery-chargers-handle-such-high-currents-amps/846769/30 "2020-01-24T07:10:09Z")
> [@Leo\_Bloom](#): > > Holy crap, gravity limits the little suckers at this scale? Yes. All else being equal, the max current capacity of a (single) wire that is oriented horizontally will be slightly higher vs. if it were oriented vertically. Stated another way: all else being equal, a (single) wire that is oriented horizontally will have a slightly lower temperature vs. if it were oriented vertically. ---
**Author:** ![48Willys](https://avatars.discourse-cdn.com/v4/letter/4/db5fbb/32.png) [@48Willys](https://boards.straightdope.com/u/48Willys)\ **Post date:** [January 24, 2020, 8:25am UTC](https://boards.straightdope.com/t/how-do-car-batteries-and-inustrial-battery-chargers-handle-such-high-currents-amps/846769/31 "2020-01-24T08:25:00Z")
> [@Marvin\_the\_Martian](#): > > Well, I was six or seven years old at the time so forgetting a few details isn’t too shocking. I think the Beetle was a 1963, so definitely 6 volt. The Microbus we got next was definitely 12 volt. > > W **as the battery under the front hood?** If so, a pretty long electrical run back to the starter so not surprising that upping the size of the battery cable helps, especially since a 6V system has less headroom for voltage drop. Bolding mine. No, the battery was under the back seat on the right hand side. About 18" from the starter. If one did not keep the positive post on the battery covered with the factory plastic lid, or some other insulator, the battery could short out on the bottom of the seat. If that happened, a fire was often the result. Many a beetle was totaled for this reason. On almost all of my type 1s, I built a 1/2" plywood cover for the entire battery. On a few of them I used a cut down truck mud flap. I never had this problem. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [January 24, 2020, 11:46am UTC](https://boards.straightdope.com/t/how-do-car-batteries-and-inustrial-battery-chargers-handle-such-high-currents-amps/846769/32 "2020-01-24T11:46:57Z")
> [@Leo\_Bloom](#): > > Holy crap, gravity limits the little suckers at this scale? I’m not sure if you are making a joke, but the reason is that wires (like most warm objects) are primarily cooled by natural convection. Natural convection just means the surrounding air is warmed up, which then rises upwards. If the wire is vertical, it rises up along the wire, so the cooling effect is less than for a horizontal wire. ---
**Author:** ![dstarfire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dstarfire/32/5762_2.png) [@dstarfire](https://boards.straightdope.com/u/dstarfire)\ **Post date:** [January 28, 2020, 7:13pm UTC](https://boards.straightdope.com/t/how-do-car-batteries-and-inustrial-battery-chargers-handle-such-high-currents-amps/846769/33 "2020-01-28T19:13:22Z")
> [@48Willys](#): > > Just to add to the confusion here, in many factories, the forklift chargers all have 3 phase 480 volt inputs. Being 480 volts means that the amperage required for them is smaller. Being 3 phase means that the amperage required for them is smaller still. This means that the wires needed for the input can be much smaller. > > The cables that attach the charger to the battery will still need to be fairly large. Keep in mind that most forklift batteries are at least 48 volts, many are in the 90 volt range. > > I can almost guaranty that each charger has its own circuit breaker on an electrical panel somewhere. I think that it is required in the national code. All of the ones that I have dealt with have been laid out that way. > > IHTH, 48. I’d forgotten about industrial power being 3-phase. And yes, each charger goes into a heavy-duty wall outlet and 1-2 (our turret trucks use 2 batteries) of these outlets will be connected to a junction box with an industrial\* switch (I’d assumed the switch was just for safety so they could turn off the sockets when the chargers were unplugged). > [@48Willys](#): > > IME, Most forklift chargers in a factory are hard wired, and do not have a plug for the input. Those chargers are bolted to the floor & are not going anywhere. Thus, no need for a plug. about 1/3 of our chargers are currently non-functional, so a plug is very much needed, at least in our facility (Amazon shipping center). We have a high turnover (including local management), so the equipment sees a fair amount of abuse. Also, they tend to redesign the floor layout every few years as usage changes. - designed in such a way that you can’t accidentally bump it from one position to another. includes support for locking a switch in one position with a padlock. [Previous page](https://boards.straightdope.com/t/how-do-car-batteries-and-inustrial-battery-chargers-handle-such-high-currents-amps/846769.md?page=1)