Buy power electronics? Watch out for them wires... (1 Viewer)

[e9999]

Rant of the day:

I'm so annoyed with the generic cheap chinese electronics... Of course, you'll say, what do you expect...? True enough, but there are limits. Or you would hope there would be.

I'm looking right now at 60A LFP battery chargers. (Dang batteries are getting big and take a looong time to charge with the wimpy chargers I have.)
Not a problem you say, should be plenty of those on Amazon. Yes, there are a few. But...

Now, for context, I have been playing with wires a lot recently, including being busy with making big enough wires to carry safely the currents I need for some solar tests. So I guess I'm oversensitive to that aspect, admittedly.

Well, I was looking at that 60A charger on Amazon. I mean 60A is quite a bit by the usual household electronics standards. I was stunned at the size of the wires that thing had on it. If I had to guess looking at the wires size in comparison to the rest of the system on the photos, I am guessing those are probably 14ga wires. Maybe 12, but I doubt it. So if you know a bit about ampacity, you'll know that a typical 12 or 14 AWG wire will not carry 60A safely. By a long shot. Might help a bit if the insulation is silicone but I think that may still be a stretch. And this one has alligator clips on it that look like 10A ones as well. So I'm thinking that those wires are severely undersized and I would not want to use that thing inside the house, and likely not at all unless I'm fully convinced it's OK (maybe if it has some unobtainium magic insulation).

Kinda like this cheap power meter I have that is "rated" at 100A but has 12AWG wires on it. (the wire connector melted at 40A).

So, anyway, folks, maybe not a bad idea to double check these wires gauges when you look at more powerful electronics if you don't want a bad surprise. I guess that's kind of obvious but I think we all to some extent count on reasonably well designed and safe electronics on Amazon, and may buy things quickly without checking much when in a hurry. Well, maybe we shouldn't.


[End of Rant. I feel better already...]




[On another sad/funny note, one of the reviewers of another but similar cheap chinese charger took his apart and discovered that they had used a really old and very cruddy surplus server power supply and simply hid it under a new shiny metal cover. Kinda reminds me of those chinese 18650s with a AAA inside and some sand for ballast that I've seen...]

 

[spressomon]

Just know SOK and Renogy don't stand behind their products including their LFP batteries, these days ...lots of complaints coming off another non-'MUD site I peruse.

 

[e9999]

I have had a really bad customer experience with Renogy in the past after getting a defective product of theirs, so am not surprised by what you say.

I was just looking at power meters and there are some -looking identical to the one I mentioned I have- still with 12AWG leads, but the meter is "rated" at 200A in the description.... It's a competition to more nonsense, apparently.

What is interesting is that in the case of these 60A chargers at least, most of the ones I saw have no reviews or only a few on Amazon. Sure looks like they are trying to make a quick buck by overselling underdesigned products to unsuspecting customers, possibly with a few fake reviews. And you see the same generic product with different names in the description (not even on the product on some). So easy to switch "Sellers" in case of trouble, I guess. In some of the few apparently legit reviews I read, there was mention of there being no company contact information at all to be found, so no way to contact them. I guess there will always be shady operators. At least, if you move fast enough, Amazon is extremely good with refunds, so that's something. I just try to not buy anything that does not have at least a few hundred reviews and a 4.5 / 5 rating. And I saw no such charger. So, need to revise my plans, apparently.

But what really bothers me about all this is the risk of fire with undersized wiring. How are they remotely willing to put people's houses at risk through bad design....?

 

[peesalot]

Seems like that should be 10 wire or even 8 for a 60 amp circuit ?

 

[e9999]

more like 6 AWG at least, I think, depending on quality of insulation, but I doubt very much that this cheap chinese stuff has expensive high temp insulation on.

I saw one similar 60A charger that looked like it had thicker wires and solid clamps and I could make out in one of the pics that this was 8AWG wire. Better.
Thing is that you can't trust the pics anyway, seen some where they were mixing pics of good and lousy clamps in the same description.




To be fair and complete, and after calming down a bit from the rant, I feel that I should reiterate / clarify that this whole ampacity thing is very dependent on the insulation. In fact, I have seen claims of high quality wire with very good silicone insulation that was reportedly able to withstand 60+A in 12AWG size. So, I suppose it is in theory possible that chargers like the one I saw could have thin wires but yet be capable of continuous 60A *if they had very high quality wires*. So you'd have to ponder the likelihood of the latter being the case. Especially if you see some really small cheap alligator clamps on the wire.

 

[peesalot]

OK but that 8awg is rated for 40amps @ 110V how does that compare to 40amps at 12V ? Seems the #8 would be more than sufficient for 40amps @ 12V ? or I am missing something ?

 

[e9999]

I would think that the overall voltage doesn't matter for ampacity. The power dissipated in the wire is dV*I but that is really R*I^2. The resistance is a function of the wire physical characteristics (and temp secondarily), not voltage (directly). So the current -not the voltage- determines the heat generated which in turn determines the temperature of the insulation and whether it will be affected or not, IOW the ampacity. But somebody correct me if that's wrong.

 

[AgentOrange]

If I remember right, the amps don't care much about the voltage. The increased voltage only means more watts. 60 amps is 60 amps. Depending on the length of the run, I'd run #4 or #2 wire to give the 80% rule some wiggle room. If you wire for 75amps, then the wire will always be cool enough

 

[spressomon]

Not protocol but a good work around for my application: I ran 1/0 from engine bay/battery into the nose box of my Escape 15A to supply current to the Sterling BB1260 (maximum 60A output). The BB1260 electrical connect receptacle has a max cable size of 6AWG for the + & - inputs. Connected the 1/0 and the 6AWG to a busbar with the 6AWG to the BB1260 being ~6" in length. No issues.

 

[e9999]

^ that sounds good, you maintain good voltage with the 1/0 if it's a long run, and many 6AWG should handle 60A. The worst one I see in the NEC ampacity chart is 55A for the 60degC insulation. Above that temp rating I see 65A and more.

I have a stash of silicone 200deg C insulation wire. That stuff is pricier so I save it for more demanding uses. That would be perfect for short runs like your 6" where you are limited by the receptacle and may be high on the amps. I don't know offhand what a silicone 6AWG would handle, but would not be surprised if it's over 100A. (Keep in mind also that it's not because a unit is rated at 60A that it won't pull quite a bit more at times. I have a "30A" DC-DC and I got in trouble cuz it was pulling 40A -maybe even 45A, I don't recall- from the source battery.)

 

[Land Shark]

OK but that 8awg is rated for 40amps @ 110V how does that compare to 40amps at 12V ? Seems the #8 would be more than sufficient for 40amps @ 12V ? or I am missing something ?

Amps are Amps

 

[peesalot]

I guess so when you compare household wire size for 15 and 20 amp breakers it would be same in rig, curious what the solid vs stranded resistance is on say a 14 & a 12 ?

 

[sdnative]

Amps are Amps

I agree that Watts are Watts, but not sure that Amps are Amps.

AC current is a sinusoidal waveform with a P-P and RMS value. I believe you may be correct if you are comparing AC RMS amps to DC amps in this context.

 

[peesalot]

Is there a difference in amps between AC & DC as far as wire size to carry the intended load ? I was comparing in my mind a 15amp 12v DC circuit to a 15 amp 110v AC circuit and other than solid vs stranded I dont see much diff.

 

[e9999]

^ I don't think so, in the big picture. There may be some subtleties like surface effects and such, but I don't think they are significant to the discussion at hand. By their very definition, the current and voltage values for AC are given in such a way that they are equivalent to the DC ones in terms of power, that's why we are using the RMS values for AC and just multiply the voltage and current to get power for AC as well, without having to worry about peak values, frequencies and such. Well, at least if we are not worried about what happens at the millisecond level. If you think about it, the 120V we are talking about for houses is not really 120V at all. In reality, the voltage varies between +170V and -170V or so. The 120V is just the DC power equivalent average, there is nothing special/visible about the 120V value if you look at the voltage trace. So, yes, the RMS (what you always hear about) for AC amps is the relevant value here because it is the basis for power calculations, including in the wire.

In any case, from what I see you writing, I think that where some of the confusion lies is that you are thinking of overall voltage as an indication of power, which would normally be correct but not in this case. It is just the voltage drop over the length of the wire that matters for the power dissipated in the wire (thus the ampacity), not the overall voltage. For example, I'm running an inverter with a 13V battery. What matters to the wire heating is not the 13V, it is the 0.4V I lose in the wires. That is a small fraction of the power spent by the battery. The rest is of course used to power the inverter. The needed size of the wire is primarily a function of what is happening in the wire, it has nothing much to do with what's happening in the inverter (besides lowering the voltage a bit). This whole business about sizing wire has 2 components: the primary one (usually, because of safety reasons) is the ampacity (sizing the wire so it does not damage the insulation by getting too hot), which is what I'm talking about in the OP, and also -not what I'm talking about here- avoiding overly large voltage drops in the wire (for load behavior purposes). These are 2 separate issues, intent-wise (although connected indirectly).

 

[sdnative]

Agreed probably not much of a difference.

 

[e9999]

It also is worth keeping in mind that the charts about ampacity and wire sizing are predicated on *continuous* use. Which are intended for safety, so a conservative value. Of course, the wire will handle a higher current than specified for some period of time, basically until it gets too hot for the insulation. That is a function of thermal inertia and also the ambient conditions. The higher the overcurrent, the shorter that period will be, naturally. The tricky part is to know what that duration is to remain safe, of course. But for instance, in practice, I would not be bothered much if I were to run 100A in a basic 10AWG wire (nominally good for only 30+A) for a few seconds. Basically if it does not feel hot to the touch, you're probably good. Having said all that, for the charger use, as in the OP, which could be for hours, I would definitely go by the charts.

 

[peesalot]

Nicely written, so back to the op idea - gimme it in laymans terms, in the rig a 6 ft , 10 wire ( stranded) on a 30 amp fuse will have how much drop ? I do not know the math and I realize the other variables but mainly am curious to run some #'s on my stuff and see if I am actually using a proper wire after looking at insulation, length, etc not just saying its a 10 wire on a 30 so its good ? And if I read your post correctly you are going deeper and taking that ? into the devices . Are you an engineer by chance ?

 

[e9999]

^ First figure out how much current you'll need to keep your load going. Then, just look up 2 charts on Google. One is the ampacity chart, that is how much wire you need to carry that given current without damaging the insulation (you'll need to know what kind of insulation the wire has); this is not a function of wire length. That's the ampacity we have been talking about. The second is the voltage drop, which is a function of wire length. You can either figure out what voltage drop you'd get for a given current, wire size, and length. Or conversely, what size you'd need for a given current, length and allowable voltage drop (to keep the load happy). If the 2 sizes you get from the charts are not the same, use the bigger one to be safe. In doubt, and if $$ are no object, always get the bigger wire, you can't go wrong. (Until you can't bend it any more.)

 

[Land Shark]

I agree that Watts are Watts, but not sure that Amps are Amps.

AC current is a sinusoidal waveform with a P-P and RMS value. I believe you may be correct if you are comparing AC RMS amps to DC amps in this context.

Yes sir. I definitely don’t have the background to talk peak and RMS values to great degree on the sine wave but do have a basic understanding of that. Electronics class was 34 years ago. Ha ha