I Almost Melted My Cables Learning This About 48V Solar

Added: 2026-05-13

[00:00:00]Uh, so I did a little off-grid experiment here a couple of days ago and I learned something that I should have known a long time ago.

[00:00:09]I was running about 1,000 watts off of these two ag cables and they got blistering hot. The 1000 watts I was pulling was running this 48vt charger.

[00:00:24]And on this system, at the very same time, these little teeny wires were barely warm to the touch.

[00:00:33]Same power, totally different behavior.

[00:00:38]So, I had a little light bulb moment.

[00:00:41]Hey, good morning everybody and welcome back to the channel. Fastmoving trade wind conditions today. About 80 degrees, lots of showers intermittently.

[00:00:52]Everything's looking pretty good. So, let me walk you through what I I learned and feel like I should have learned it a long time ago. A lot of you guys have painstakingly walked me through this before. I think it finally sunk into the gray matter. Okay, so I had 200 amp hours sitting there fully charged, ready to go.

[00:01:15]And they're tied into a 3000 watt pure sinewave inverter.

[00:01:21]had my trusty watt meter plugged in so I could see exactly what it was doing. And I turned it on and let it rip.

[00:01:30]Yeah.

[00:01:34]1,50 watts.

[00:01:38]Yeah. Now that inverter stopped making noise, but you can hear how quiet that is.

[00:01:51]17.7 amps going in. And I did just check my Victron app and I've got about 50 watts coming in off of 900 watts available there cuz the sun isn't really up yet.

[00:02:10]And while that charger was running, I was watching this and and I was watching the percentile click up nice and fast actually. I mean, it was down to 90ome percent and I could watch this click over every, you know, few seconds or so really. It wasn't taking very long and I was very happy. And the first things I was doing, I was like testing, you know, how hot are these getting? How hard are these getting? And then I'd come back over here and I'd watch and I was like, "Oh, look. It clicked up again. It clicked up again. Oh, I'm loving I'm loving this charger." Right.

[00:02:49]And it must have been, I don't know, 2 minutes. And I started smelling plastic.

[00:02:55]And I kept going, "Oh, oh, these little wires, they don't feel hot."

[00:03:00]And then I jumped over to here and I went like that and I could not hold that. This thing was blistering hot. So, I quickly shut the system down. Yeah.

[00:03:08]So, that's when the light went off. And in the heat of battle, what wasn't making sense in my brain was those great big cables were blistering hot. And those little teeny ones, barely any warmth to them whatsoever.

[00:03:26]And then I heard a little voice, might have been one of you guys in the background saying, "Watt watts."

[00:03:34]But current changes drastically depending on the voltage.

[00:03:39]Yeah.

[00:03:41]12 volt needs huge current.

[00:03:44]48 volt moves same power easier.

[00:03:50]And wire heating follows current.

[00:03:55]1,00 watts here, roughly 100 amps versus about 18 amps, 20 amps on 48 volt.

[00:04:07]Just amazing, right?

[00:04:11]One of the things I love about living this way is the systems I live on keep teaching me things.

[00:04:20]I'm always reading and watching and listening to you guys about things to do differently.

[00:04:30]But it wasn't until I smelled rubber burning that I got a real education.

[00:04:40]Wire sizing really, really matters. And it's why a lot of off-grid homesteaders are really gravitating towards 48 volt especially over the past few years with the uh introduction of lithium iron phosphate batteries as our uh you know power system storage tank. Different than the lead acid days, right?

[00:05:08]So what are some of the stories in your off-grid experience uh where you even after years uh you know got the light bulb moment?

[00:05:21]Yeah, they still happen.

[00:05:25]So, I did talk to AI this morning and as I was doing that, I could hear uh our good friend Matt in the background and I was remembering his comment when we were talking about AI and how I am very late to the game with AI as I have been about a lot of technology.

[00:05:48]And as I was getting ready to ask my question, I remembered he said, "You need to know what question you're asking, you know." Um, so I was very mindful of that. And I'm just sitting there having my coffee going blah blah blah like I do to myself in the morning uh just out loud so AI could try to make sense of what I was asking because I remember him saying you know if you don't ask the wrong right questions uh you might be doing yourself more harm than good. So, I was mindful of that.

[00:06:28]And I'll read you for those of you interested what I said uh in a blah blah blah form and what AI told me about this topic. And it was very good. And I'm going to keep rereading it because Yeah. So, here we go. All right. Here it is word for word. So, okay, I want to ask a question and I hope I do it the right way. So, I as an experiment, I tried to hook up my 58.4 volt 18 amp 48vt charger. I tied it into a 12volt system with two aug cables on the batteries and a 3000 watt inverter.

[00:07:12]It said I was pulling a,50 watts and I was noticing that the two gauge cables got too hot. So, I was pretty close to exceeding what I could pull off of those cables. But interestingly enough, the charger was charging 18 amps into my 48vt system with no more than 10 or 12 gauge wires hooked to my bus bars and they didn't get hot. Can you explain to me how this is happening?

[00:07:39]Took AI all of about 1 second to say yes. And what you observed actually makes sense uh perfect sense electrically.

[00:07:48]The key is the power stays roughly the same, but current changes dramatically with voltage.

[00:07:54]You were essentially using a 12volt battery system to feed a charger that was outputting power into a 48vt battery system. Here's the important relationship. P= V * I. So higher voltage, lower current for the same power. lower voltage, much higher current for the same power. In your case, on the 48vt charging side, your charger was outputting 58.4 volt * 18 amps equals 1,51 watt. So, the charger was delivering about 1,50 watts into the 48vt battery bank. That means the wires from the charger to the 48vt bank only had to carry 18 amps. That's why your 10 or 12 gauge wiring stayed relatively cool. 18 amps is not a huge amount of current on the 12vt side. But the inverter feeding that charger had to supply the same 1,000 watts from only 12 V. So now the math changes. 1,00 watts divided by 12 V equals 83 amps. And realistically because of inverter loss you are probably p pulling more like 90 to 100 amps continuous maybe even higher in surges. That is a lot of current.

[00:09:17]Why the two gauge cables got hot. Heat in cables is mostly caused by current not wattage directly. The heating effect follows this relationship.

[00:09:28]P loss equals I^2 R. That I squared part is huge. If you double current, heating goes up four times. So 18 amps on the 48vt side, modest heating. 90 plus amps on the 12vt side, major heating potential. Even good two aug cables can get warm if the run is long, lugs aren't perfect, crimp resistant resistance exists, inverter terminals are slightly resistive, or you're pulling near 100 amps continuously.

[00:10:07]What you discovered, you basically rediscovered one of the biggest reasons higher voltage systems are so attractive for off-grid living. 12volt systems become extremely heavy at high power.

[00:10:20]48vt systems move the same power with far less current. Less current means smaller wire, less voltage drop, less heating, higher efficiency. That's why 1,000 watts on 12vt is brutal. 1,00 watts on 48 volt is easy.

[00:10:38]And honestly, your observation that the smaller charger output wire stayed cool while the giant two aug battery cables heated up is exactly what electrical theory predicts.

[00:10:53]All right.

[00:10:55]Just like what a lot of you guys know, like the back of your hand and what you have told me over the years. and it just didn't sink on sink into me until I smelled it happening.

[00:11:11]So, in conclusion, I've basically given up trying to use this as a, you know, a system to rob from here to put into the 48vt system and just continue to use it as a backup system. I mean, for my purposes, if if this system gets drained down, uh I can always just switch over to that other system and run my refrigerator freezer. And if I choose not to, you know, I'll fire up the generator and use this, no problem.

[00:11:49]Still learning, my friends, and it feels good to be doing that. and thanks for all your contributions and comments over the years. Uh yeah, funny how you learn things sometimes.

[00:12:06]Aloha everybody. Be well in your neck of the woods. Things are good here.

[00:12:11]Real good. Yeah.

[00:12:13]What do you think about all that? Huh?

[00:12:20]Yeah. Could have been worse. Oh, I just thought of another question to ask AI.

[00:12:27]Stop laughing at me, would you?