Wire Type

rockypro1

10 W
Joined
Jan 20, 2018
Messages
69
Location
Ireland
Hi,

Today I went to get some wire at my electrical store. Its to go from my 48 volt 20 ah battery to the controller.
I was looking for 12 awg red and black. As been for electricity I thought it would be great cause it it can carry 240 volt here in Ireland,
it would work on a 48Volt battery. The guy said if I use it it will melt and burn out the battery, controller or hub.
He said I have to get this only for my e-bike == 12 awg 200c 3135 single cable ===

Link https://www.amazon.co.uk/dp/B07CBJ9VGH/ref=sspa_dk_detail_3?pd_rd_i=B07BYRGYMJ&pd_rd_wg=RB6db&pd_rd_r=MD00D2P09JMH4EYQDRJP&pd_rd_w=mlW2X&th=1

Is the right or what do you's think.

Thanks
 
keithd said:
12 AWG is rated to 20 AMPS I would think you want wire rated higher than your intended max amps

Ok. What gauge do you recommend yourself. Its just that the wire from the controller and battery are 12 gauge, the wire from the battery is 200c heat proof but the wire from the controller is not.
 
20 ah is the capacity of the battery. That doesn't really matter.
What matters is the motor current or how many watts the motor will take.

If the motor is limited to 20A, then 12ga will be fine. It will barely get warm. I've run 50A with 12ga.
Using heavier wire is OK, but probably unnecessary.
 
The thickness of the wire has a minimal relationship with the voltage. The characteristic of concern is the heat that results from amps.

There is a "continuous" and also a "temporary peak" amp-rating for wires. For a 20A max controller, you will be fine with 12GA.

If this was for an application where you would be flowing 20A continuously? Perhaps a thicker wire would be appropriate, but...your ebike will only draw the max 20A on occasion...
 
Turnigy silicone wire at Hobby King! All sizes, all colors.
Luv the stuff.
 
Thanks for the replies guys. very helpful.
I'm going to order some online. Can't find any where I live.
Cheers
 
I would not use any wire on my ebikes which does not have any marking on it.
Do you believe description on vendor web site or description printed on wire itself?
 
I have a 2kW hub motor having 40A cont. current and 60A max current rating. Please suggest suitable wire gauge for my application.
 
Supply house guy is actually pointing you in the right direction with the 200deg teflon coated silicon wire. But they wont stock that

12awg wire is rated 20a for household use but if its only 2’ of cable on a bike 12awg can draw 40-50a before it gets hot/unusable

If you want to buy something the supply house will stock ask them for a 5’ cut of SJEOOW 12/3 awg flexible cord. It should be like .60 cents per foot. This cable will have three 12awg fine stranded copper conductors you can cut out of the cable. If you think 12awg is too small ask for SJO 10/3 cable which is 30a industry rated.
 
What he said, partly because of the short length on a typical bike, 12g many stranded RC wire works fine to about 40 amps,

This is also because you never pull all 40 for that long a period, unless you are towing a 500 pound trailer or something.
 
The silicon shielded high strand count wire is nice to use. I went with 6awg for both phase wiring and battery personally. I plan to likely end up pulling around 150 amps so that seemed fairly reasonable and 4awg was too big. I see a lot of 12g wiring and questionable connections and bus bars. 12 or 10awg is fine for most small builds as long as the length is kept to a minimum and they are fused to protect the wire. If you find the insulation getting stiff over time that is a good indication of inadequate gauge. I would make a goal of having as low of resistance in the system and possible to minimize voltage sag under load.
 
Ratings for wires vary a lot, look online for wire tables that give some numbers. One table that I often see come up in searches is this one:

https://www.powerstream.com/Wire_Size.htm

For #12 wire this table shows 41 amps in chassis and 9.3 amps in power transmission. These continuous current values represent a range based on different operating conditions and design assumptions. I regard the 41 amp value as a maximum continuous value for most use cases (and de-rate from there). Since heating increases as the square of the current things go bad rather quickly as current is increased.

The length of a wire doesn't really change the current handling capacity. Adding length adds both power loss through I squared R (R is proportional to length) and at the same time increases the cooling surface area. So it basically cancels out. For this reason most wire tables don't discuss or show wire length as a factor in current capacity.

A major factor in how much current the wire can handle is what temperature it will operate at. The ability of the insulation to withstand high temperature is important here. Unfortunately some of the highest temperature insulations (like silicone) are very soft and easy to damage so tight tie wraps or metal edges can penetrate the insulation and cause shorts. This is also a problem with PVC insulation when it gets hot and becomes soft.

When wires are bundled together the heat from multiple conductors generates higher temperatures, so multiple wires in a bundle call for reduced current.

If there is good airflow the heat will be carried away faster and somewhat higher current can be carried. This is often true in RC applications, and in some ebikes, for example the wires to the motor probably get good airflow. The battery side wiring may be covered and not get good airflow however.

If you like your wiring to operate without getting hot then choose a little heavier wire. You will notice the wire get warm when charging if you have a high current charger. I was using #14 wire for charging at 12 amps. This table shows 5.9 to 32 amps for #14, but at 12 amps continuous it gets fairly warm in still air. The wire is also called on to provide cooling for the connector, so near the connector it was even warmer.

On that same bike I use two #12's in parallel for battery to motor current, giving it a max capacity of about 80 amps. The controller is set for 80 amps max, and those levels of current don't last long, so the wiring does not get warm that I've noticed. In this case it was easier to work with a pair of #12's than a heavier wire as we were paralleling four 8AH Lipos.

The heating of the wire wastes a small amount of energy. It is not a lot, but using heavier wire does increase efficiency slightly. Length matters here, hence the lower values of current recommended in the table for power transmission to avoid wasting too much power. Make the wires long enough, but no longer. Keeping length at a minimum plus and minus paired also reduces inductance which is important between the controller and the battery as additional inductance increases the voltage spikes on the FETs. On the motor side inductance and cable length is much less of a concern.

Stranding of the wire is important for flexibility and long life in the face of vibration. Finer stranding maximizes flexibility. The stranding in house wire is not really sufficient for ebikes. Automotive or marine grade wire is a better choice.
 
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