I purchased an AGM lead acid deep cycle battery, inverter and solar panels. All of the provided cables connecting these devices were made of thick copper.

I also have Goal Zero Yeti 400 lead acid battery which has a built-in inverter. I wanted to chain this to another AGM battery using its mini Anderson plug port. I went to an electrical shop and they gave me what I needed to chain the batteries and it’s all working fine. The cables that they gave me for connecting the chaining port to the terminals on the second battery were much thinner cables made of a silver coloured metal. What metal is this likely to be? The copper cables are a lot more expensive per metre and look much more robust. Are the thinner cables satisfactory or should I be using the thick copper cables for this purpose?


I can confirm that the wire is tinned copper 5x3.2mm (WxH), PVC insulated, maximum temperature 80°, rated current 7.5A, stranding 24x0.2mm, diameter 1.9mm, AWG 18. It chains the 2 batteries via a 45A Anderson powerpole connector set. The length of cable between the 2 batteries is 2m.

The purpose of my question is to prevent a catastrophe (such as a fire) and I am trying to quantify the capability of this setup. What are the quantitative limitations? Am I on the edge or well within safety limits based on the information I have provided? It’s working well so far but want to avoid any surprises later on.

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    \$\begingroup\$ As with all questions that start out with "What is the best ...", you MUST define what "best" means to you in your application. What is most important to you: Cost? Flexibility? Efficiency? Aesthetic appeal? \$\endgroup\$ – Dave Tweed Jan 3 '18 at 15:06
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    \$\begingroup\$ AWG18 is a bit light for ~20A service (from your comment below), especially at low voltage. I would recommend AWG12 as a minimum. \$\endgroup\$ – Dave Tweed Jan 3 '18 at 22:09
  • \$\begingroup\$ @DaveTweed What would you say is the maximum amperage I should draw with AWG 18? I have briefly drawn 220W though i believe it has a 200W inverter. I can comfortably stay well inside this (<150W) and I’ll need to in order to get the daily life I’ll need from my battery and solar panel capacities. \$\endgroup\$ – Guru Josh Jan 3 '18 at 22:35
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    \$\begingroup\$ AWG18 is 20 mOhm/m, so if you can tolerate a 5% drop (0.6V @ 12V nominal), then your 4 meters of wire could handle about 7.5A (interestingly, the same number as the "rating" you quoted above). 15A would give you a 10% drop in voltage. AWG12 has 4x the area (1/4 the resistance), giving just 0.4V drop @ 20A. \$\endgroup\$ – Dave Tweed Jan 3 '18 at 23:09

The metal is likely to be tinned copper.
If the wires that the electrical shop (sic) gave you is satisfactory or not, is up to you, according to what current you expect to go in the wires, and what voltage drop you accept over the cable (and secondary, max temperature of the insulation material on the wires)
EDIT: According to new information; If what you want to avoid is heat buildup and fire, what you need to do is choose heavier gauge wire. The heavier the gauge, the less heat is built up. If the wire is rated for 7.5A max, then that is what I suggest you stick to, unless you are comfortable with making the appropriate calculations and following criticality evaluation yourself.

Anyway, the answer to your question regarding material is still: Copper - tinned or not. For more info on choosing the correct gauge, see Here and here

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  • \$\begingroup\$ Are the thick copper wires significantly superior? Without fully understanding all of these variables, would it be best to use the thick copper wires to cover all possibilities? They are 12V batteries drawing no more than 250W so looking at around 20 Amps maximum. What sort of amperage can tinned copper accommodate and what are the consequences of significantly exceeding this? \$\endgroup\$ – Guru Josh Jan 3 '18 at 14:57
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    \$\begingroup\$ Significantly superior does not mean anything in this context. Superior at what? Superiority is not a quantitative measure that can be compared. It is the same material, with a surface treatment, so tinned copper will carry current just as well as non-tinned (in this application anyway). You have not specified the gauge of the wire you purchased. The current carrying capacity of copper is not the limiting parameter - like I said, its voltage drop across wire and maximum allowed temperature increase. The consequence of exceeding the current carrying capability of a conductor is fire. \$\endgroup\$ – MrGerber Jan 3 '18 at 15:04
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    \$\begingroup\$ Thick copper wires does not mean anything either. Thick is not a quantitative measure. For line workers, thick copper conductors is probably going to be finger thickness, but for finer electronics work, AWG 18 would be considered thick. \$\endgroup\$ – MrGerber Jan 3 '18 at 15:08

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