What AWG wire for 52v battery?

paulstung

100 W
Joined
Jul 18, 2016
Messages
124
On my original bike I was running a 60v 23amh.battery but the bms blew and I've just had it lying around doing nothing so I'm going to reuse the cells for my next build a 52v not sure on the amh as of yet, I've not got that far in the figuring out of things with the frame.

I've not got a spot welder so I'm going to use silicon wire instead of nickel strips. The bms I'm going to use is probably a 50A, do my question is what's the best awg wire to use. The cells are the LG GBMG11865

Thsnks guys..
 
Just like a fuse or circuit breaker, the BMS protects both the device and the wires. So if you use a 50A BMS, the wire must be rated for at least 50A.
But since wire current rating is determined by insulation, you have to find the current ratings for the specific wire you're going to use to select gauge.
When unsure, I like 10AWG, as it is compatible with the most relevant connector families.
 
fatty said:
Just like a fuse or circuit breaker, the BMS protects both the device and the wires. So if you use a 50A BMS, the wire must be rated for at least 50A.
But since wire current rating is determined by insulation, you have to find the current ratings for the specific wire you're going to use to select gauge.
When unsure, I like 10AWG, as it is compatible with the most relevant connector families.

Ampacity is determined not by insulation, but by conductor cross-sectional area.

https://www.powerstream.com/Wire_Size.htm
 
Hello sure there are people on here more qualified work out correct answer but I can point you in right direction , there are data tables online link provided by Chalo above that give amp rating for each awg, a useful tool for selecting correct wire for application, I also like to check specs of particular cable I purchased, your controller peak output is an important number as this determines selection of BMS in your case 50 amps and size of battery and main discharge wires with bit added on for safety, with regards to cell connections the wire can be thinner but depends on battery cell configuration And how many series connections you are able to make between your parallel groups divide total discharge ( BMS peak not continuous) by that number with little bit on top for good measure, your parallel connections size are determined by parallel cell group number and cell amps ,if you are planning on soldering connections be aware of dangers involved :mrgreen: Peace
 
Chalo said:
Ampacity is determined not by insulation, but by conductor cross-sectional area.

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

That chart is trash and you are wrong.

That chart uses NEC, 700, circMils/Amp, and we can easily get away with much less inour (EV) builds for we do not need to subscribe to insurance regulations ( like 700CircMil/Amp) for our bike is not being insured.... and u can use like 25o (CircMilsPerAmp) ballpark.

That chart is trash...; for people who worry about insurance regulations: ( like Helmet laws for motorbikes, but not for bicycles, one is insured and expensive, there is DATA on it, is required by LAW, one is NO DATA and noone cares, not required by LAW cause noone does expensive damage ) ( Like burn a home down or kill someone, expensive) Chalo... ) . Most online charts are trash.

The ampacity of a Cu conductor depends on the temperature rating of the insulation.

The effect of resistance to current flow is heating and this is dependent upon the size of the conductor, the insulation material around the conductor, and the installation environment. ... Similarly, the higher the temperature resistance of the insulating material, the higher the ampacity or current carrying capacity.

Cable ampacity of a single conductor is calculated based on the size of the electrified conductor, the established ambient temperature and the temperature rating of the insulation and jacket compounds. An increase in temperature rating of the compounds and/or an increase in conductor size will increase cable ampacity.

Ampacity is defined as the maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. The ampacity of a conductor depends on its ability to dissipate heat without damage to the conductor or its insulation. This is a function of the insulation temperature rating, the electrical resistance of the conductor material, the ambient temperature, and the ability of the insulated conductor to dissipate heat to the surrounds.

For 50A, 10g is fine, 8 Ga is better, but you could get away with 12g auuge. On our little bikes.

I
n many instances, a circuit’s unique application correction factors (as described above) will warrant the need for ampacity adjustments. There are four conditions that will determine whether a correction factor is required:

1) Ambient temperature – The temperature rating of a wire must include the ambient temperature in the application. If the temperature rating of a wire is 90°C and it needs to be placed in a 75°C ambient condition, then the allowable temperature rise of the wire is 15°C (90°C minus 75°C). In this example, the Ampacity of the conductor size specified will need to be de-rated by 50% (based on being limited to a 15°C rise instead of a 30°C rise).
2) Duty cycle – many times the level of current in applications will vary over time depending on the type of loads. Electrical motors, for example, draw a large amount of current at start up for a short period of time and then the current level reduces as the motor reaches the steady state rpm. In these cases, the wire size is selected such that the temperature rise of the wire does not exceed 30°C.
3) Overall system requirements – Consider the load and maximum temperature rating of the devices and equipment that make up the electrical system. Sometimes they can be the limiting factor and not the wire. In other cases, the equipment can generate its own heat which will require a higher temperature rating for the wire.
4) Effect of adjacent load carrying conductors / rate of heat dissipation – More than three current carrying conductors (ground wires are not considered current carrying for these calculations) in a cable or conduit or enclosure affects the ampacity of the wiring as described above. In some cases, multiple wiring systems that generate heat are placed together in a common enclosure that impedes the ability of the wiring to dissipate its own internally generated heat which causes additional temperature rise. This condition also requires that each circuit be evaluated to confirm that the maximum 30°C temperature rise is not exceeded.
 
If you're getting enough heat to cook regular PVC insulation, you're doing it wrong. Higher temperature means more resistance, which gives you even more heat, etc. Even if you avoid a thermal runaway situation, you'll dump some of that unnecessary heat through the conductors into the battery and electronics. It's no good.

I've mentioned several times before that parts of the power circuits in our e-bikes (like PCB traces and FET legs) have smaller effective wire gauge than what we use in cables. They can get away with this because the distances are short and there's adequate heat sinking for the relatively small amounts of resistive heat being generated. To some degree I think this principle applies to hub motor phase leads too.

When I first began consulting the chart I posted, it allowed for gauges lighter than what I had been using when I only consulted ohms/ft tables. Now I use 14ga zip cord in places where I used 12ga or even 10ga cord before. It's better balanced with the Anderson Powerpoles I typically use for battery cables. For short, <1m cables that run in free air along the frame tubes, I have even pushed 10% higher than the chart's recommended limits, to 35A with 14ga wire. I wouldn't do it to a customer's bike that I might not get to inspect afterwards, but in my own bikes I've had no problems so far.
 
Thank you all, very good info.

With regards to soldering directly onto the cells kind of. The pack I'm converting is a 16s, 9p and are already spot welded, I'm just going to carefully remove 2 from each series row, and when rebuilding just solder the parallel connections. If that makes sense...?
 
OK, that should work. You don't want to solder directly to the cell bottom. You can solder to an existing spot welded nickel strip. You still need to be careful not to overheat the cells.
 
Big soldering iron 60amp 80amp and flux. plus a damp spronge for fast cooling. leave the biggest parallel strips. less Soldering the better.
 
Back
Top