Very useful demonstration of under sized cables. There are other improvements you need to consider for safety. Lithium batteries can deliver very high currents under fault conditions, in the region of 7000 amps. This requires fuses that can tollerate this. Recomended are classT or MRBF in suitable fuse holders, as 'master fuses'. Idealy each battery should have this fuse type as close as practical to the positive terminal before any other connection. Its necessary to have positive and negative buss bars to avoid stacking more then two lugs where you have multiple cables on a common point. Where there is a reduction in cable size a suitably rated fuse are needed. The battery manufactures claim of 'drop in' replacement for lead batteries needs to approached with some caution. Under charging they tend to 'pull' more current than lead batteries. Thus chargers and cables must be able to handle this without overheating. Whilst litthum batteries are fairly tollerent of charge voltages, optimum charge volts of absorbtion 14.2 volts and float volts of 13.5 are low stress values.
Ah so run the old cables in parallel with the new ones? Good idea, provided the stack of terminals doesn't introduce more resistance than the cable. I'm probably ok with these thick cables but it's a good point I hadn't even thought of! Thanks!
This has to be the most informative video I have seen on RUclips regarding Cable Selection and Vd on DC and its inherent effects. The power gains to the load attributed to I^2 X R has been fenomenal in this case due to larger cable selection and consequently a drop in R. Not sure what type of cables used if CCA or solid copper though?. Well executed.
Thanks so much, glad you enjoyed it! You're right there are gains to be made, and I probably didn't point this out as well as I might have. 160A at 10.9V (2:44) means the inverter was receiving about 1750W of power with the old cables, but at 7:03 it's 170A and 11.6V which is nearly 2000W. So my old cables were essentially being a 250W bar radiator!
Hey Greg, can I suggest a thermal imaging camera if you don't already have one? I just got a pretty cheap (relatively) little one that connects to my phone from Infiray. Super handy when it comes to quickly finding stuff that's overheating. Thanks for sharing your experiences!
Great suggestion! I've briefly thought of those before but the cost has put me off. But I'll look further into it in case I can find a more affordable one
Great video. I recently replaced my caravan AGM setup with 300a of lithium. Fortunately I've only got 1000w inverter but you've got me thinking. Pretty sure my Anderson plug cable running from the vehicle is undersized too.
Glad it helped! Yep the charging cable from the drawbar, as well as the charging cable in the vehicle itself from the battery, should all be considered. Good luck!
G'day Greg great video. I'm sure it will help people, but you did miss the elephant in the room. That fuse was screaming 450amps. The fuse is there there to protect the cables not the load. On the first run that fuse should have been one hundred amp. Maybe up to 250amps after changing the cables, depending on what cable chart you use. Great test. very entertaining
Interesting thanks Joel! The 450A fuse shipped with the 3000W inverter and they were installed together, so it's primarily there to protect the inverter. However implicit in that statement is that the rest of the system can handle more than 450A, so as you say the fuse should be first thing to go and not the cable. However it's interesting that the inverter has a max continuous input current rating of 375A, but peak up to 450- 500A, and the cable iTechWorld supplied with the inverter had 300A stamped onto the lug. So a bit of a mishmash of specifications there! I think they're designing the fuse to blow if the inverter shorts, and assuming the install will make sure the rest of the system can handle more than 450.
@@TheMusingGreg I would change the 300A for the same 95mm cable as well. That 450A fuse will hang in there and take more than its rating before it blows. Cable insulation also has a temp rating and some good ones can go up to 200degC or a standard could be as low as 60degC.
@@sparkletornado5890 Yeah I've thought of that; but under normal circumstances the inverter will only be drawing 250A when it's generating 3000W, so it's only in overdrive conditions, which would be rare and brief, that you might pass 300A, and only in fault situations it should head north of 400A. That said the voltage drop at 250A still may be significant so I'll consider it.
@@TheMusingGreg Using the correct cable size for inverter loads helps to minimize voltage ripple, which can be detrimental to system performance. To measure ripple, set your multimeter to AC voltage mode and take a reading at the DC terminals. A ripple of 1.5-2V is considered high. Excessive ripple forces the inverter to work harder, leading to increased strain on the system and causing micro-cycling of the battery, which accelerates cell aging.
@@sparkletornado5890 Yep that's a good point mate, especially with variable loads on the inverter. If it has to battle the output load climbing as well as the input voltage dropping, and then those two factors varying quickly, it makes everything work harder. My van is out at the moment but I would expect with those thick cables there wouldn't be much ripple in my system.
Yes indeed. Amps are the killer for cable size and always use a fuse with less rating than the cable can handle. A small error can indeed burn down your pride and joy.
You're right there Peter, no point your cables becoming the fuse! It's interesting iTechWorld supplied the 3000W inverter with a 450A fuse but only 300A-rated cables (based on what's stamped on the lugs). That said, being a 3000W inverter it's really only designed to draw 250A under full continuous load, 350A for 10 seconds and 450-500A for 2 seconds. So in normal use they would be fine and I guess a temporary overload of short cables like that isn't going to be a problem, and if there's a genuine fault then the fuse should blow fairly quickly.
Not a bad thought; while the inverter usually only draws 250A at 3000W, it can draw up to 4500-6000W for 2 second bursts, which is 375-500A, which I guess is why they use a 450A fuse. Busbars are a good idea, it never occurred to me. Probably cheaper than chunky cable too.
I agree a higher voltage system is definitely one way around this problem, especially for a brand new installation where you're doing it all from scratch. However if you're retrofitting it to an existing 12 volt system, you have to factor in the cost of changing 12v appliances to 24 or 48v, plus 12 volt converters when needed to run lower power 12 volt systems like water pumps or the radio. It would probably cost more to change all that than the cost of upgrading a few cables and keeping it all as 12 volts.
Yes, there is some bad system design there. Undersized cables with a very high amp load!. No one to blame there but the installer! Properly size battery cables for the loads is simple. there are apps you can download on your phone to calculate the correct wire sizes
Haha well that installer would be me! :D The old orange cables were what linked the two original AGM batteries, but when I first installed the inverter I supplied that thinner red cable I had from an old 1200W inverter. As I had AGM batteries I was only drawing small loads from the inverter for some time, but having just changed to lithium I was able to load the inverter right up for the first time, which is when this problem first presented itself.
I don't think these are CCA cables? What made you think that? I would certainly agree in principle with what you're saying if they were. For anyone else reading this, CCA stands for copper clad aluminium, which is copper on the outside but cheaper aluminium the rest of the way through.
You’re not the first and you won’t be the last. I’m a technician by training and you would rightly assume that I knew what I was doing. But alas no! 12 volt seems safe but start talking in terms of 100, 200, 300 amps and things can get very nasty very quickly. A very similar mistake to yours in fact. Overestimating cable size is a real trap!
Thanks for the comfort! Yep I'm a tech by trade too and the simplicity of the swap meant it just didn't occur to me. But as you say at those levels of current, all sorts of innocuous conductors suddenly turn into bar radiators!!
@@TheMusingGreg I’ve literally just upgraded my very small caravan to the same system as you, except one more battery. 360 amps worth and the 3kw inverter. I used a 20mm x 6mm busbar between batteries in parallel and they actually changed colour!! Yikes! Great channel Greg you should post more often.
Wow that's scary! Glad you're liking the channel, yeah I'd like to post more often and I've actually got the content for a number of videos all recorded, but it just takes so long (as in, numerous full days back to back) to pull all the different clips together into a decent video! So everything else including work has to go on hold while that's happening. I think in some respects I may have set myself unrealistic expectations with those really long solar blanket reviews which took weeks of solid work to produce, but don't want to follow them up with half-baked content! I've definitely got the iTechWorld battery review coming, and Hard Korr has sent me an updated version of the blanket I reviewed last year to look at, so hopefully they'll be done before too much longer!
Sorry I meant to add in the link in the description! Just done that but here it is again: www.solar4rvs.com.au/buying/buyer-guides/ultimate-dc-cable-sizing-system-calculator-for-rvs/
![Stromae, Pomme - “Ma Meilleure Ennemie” (from Arcane Season 2) [Official Visualizer]](http://i.ytimg.com/vi/1F3OGIFnW1k/mqdefault.jpg)
Very useful demonstration of under sized cables.
There are other improvements you need to consider for safety.
Lithium batteries can deliver very high currents under fault conditions, in the region of 7000 amps. This requires fuses that can tollerate this. Recomended are classT or MRBF in suitable fuse holders, as 'master fuses'. Idealy each battery should have this fuse type as close as practical to the positive terminal before any other connection. Its necessary to have positive and negative buss bars to avoid stacking more then two lugs where you have multiple cables on a common point. Where there is a reduction in cable size a suitably rated fuse are needed.
The battery manufactures claim of 'drop in' replacement for lead batteries needs to approached with some caution. Under charging they tend to 'pull' more current than lead batteries. Thus chargers and cables must be able to handle this without overheating.
Whilst litthum batteries are fairly tollerent of charge voltages, optimum charge volts of absorbtion 14.2 volts and float volts of 13.5 are low stress values.
All good points, thanks Michael!
Tip, next time when you switch the cables put the old one also on top of the new ones and the voltage drop will be more less.
Ah so run the old cables in parallel with the new ones? Good idea, provided the stack of terminals doesn't introduce more resistance than the cable. I'm probably ok with these thick cables but it's a good point I hadn't even thought of! Thanks!
This has to be the most informative video I have seen on RUclips regarding Cable Selection and Vd on DC and its inherent effects. The power gains to the load attributed to I^2 X R has been fenomenal in this case due to larger cable selection and consequently a drop in R. Not sure what type of cables used if CCA or solid copper though?. Well executed.
Thanks so much, glad you enjoyed it! You're right there are gains to be made, and I probably didn't point this out as well as I might have. 160A at 10.9V (2:44) means the inverter was receiving about 1750W of power with the old cables, but at 7:03 it's 170A and 11.6V which is nearly 2000W. So my old cables were essentially being a 250W bar radiator!
Hey Greg, can I suggest a thermal imaging camera if you don't already have one? I just got a pretty cheap (relatively) little one that connects to my phone from Infiray. Super handy when it comes to quickly finding stuff that's overheating.
Thanks for sharing your experiences!
Great suggestion! I've briefly thought of those before but the cost has put me off. But I'll look further into it in case I can find a more affordable one
Great video. I recently replaced my caravan AGM setup with 300a of lithium. Fortunately I've only got 1000w inverter but you've got me thinking. Pretty sure my Anderson plug cable running from the vehicle is undersized too.
Glad it helped! Yep the charging cable from the drawbar, as well as the charging cable in the vehicle itself from the battery, should all be considered. Good luck!
G'day Greg great video. I'm sure it will help people, but you did miss the elephant in the room. That fuse was screaming 450amps. The fuse is there there to protect the cables not the load. On the first run that fuse should have been one hundred amp. Maybe up to 250amps after changing the cables, depending on what cable chart you use. Great test. very entertaining
Interesting thanks Joel! The 450A fuse shipped with the 3000W inverter and they were installed together, so it's primarily there to protect the inverter. However implicit in that statement is that the rest of the system can handle more than 450A, so as you say the fuse should be first thing to go and not the cable. However it's interesting that the inverter has a max continuous input current rating of 375A, but peak up to 450- 500A, and the cable iTechWorld supplied with the inverter had 300A stamped onto the lug. So a bit of a mishmash of specifications there! I think they're designing the fuse to blow if the inverter shorts, and assuming the install will make sure the rest of the system can handle more than 450.
@@TheMusingGreg I would change the 300A for the same 95mm cable as well. That 450A fuse will hang in there and take more than its rating before it blows. Cable insulation also has a temp rating and some good ones can go up to 200degC or a standard could be as low as 60degC.
@@sparkletornado5890 Yeah I've thought of that; but under normal circumstances the inverter will only be drawing 250A when it's generating 3000W, so it's only in overdrive conditions, which would be rare and brief, that you might pass 300A, and only in fault situations it should head north of 400A. That said the voltage drop at 250A still may be significant so I'll consider it.
@@TheMusingGreg Using the correct cable size for inverter loads helps to minimize voltage ripple, which can be detrimental to system performance. To measure ripple, set your multimeter to AC voltage mode and take a reading at the DC terminals. A ripple of 1.5-2V is considered high. Excessive ripple forces the inverter to work harder, leading to increased strain on the system and causing micro-cycling of the battery, which accelerates cell aging.
@@sparkletornado5890 Yep that's a good point mate, especially with variable loads on the inverter. If it has to battle the output load climbing as well as the input voltage dropping, and then those two factors varying quickly, it makes everything work harder. My van is out at the moment but I would expect with those thick cables there wouldn't be much ripple in my system.
Yes indeed. Amps are the killer for cable size and always use a fuse with less rating than the cable can handle. A small error can indeed burn down your pride and joy.
You're right there Peter, no point your cables becoming the fuse! It's interesting iTechWorld supplied the 3000W inverter with a 450A fuse but only 300A-rated cables (based on what's stamped on the lugs). That said, being a 3000W inverter it's really only designed to draw 250A under full continuous load, 350A for 10 seconds and 450-500A for 2 seconds. So in normal use they would be fine and I guess a temporary overload of short cables like that isn't going to be a problem, and if there's a genuine fault then the fuse should blow fairly quickly.
I would change that fuse to a 250 amp fuse. I would also use busbars to connect each battery.
Not a bad thought; while the inverter usually only draws 250A at 3000W, it can draw up to 4500-6000W for 2 second bursts, which is 375-500A, which I guess is why they use a 450A fuse. Busbars are a good idea, it never occurred to me. Probably cheaper than chunky cable too.
Silly this 12v madness. Just upgrade to a 24, or 48V system. Way lower currents and more efficient.
I agree a higher voltage system is definitely one way around this problem, especially for a brand new installation where you're doing it all from scratch. However if you're retrofitting it to an existing 12 volt system, you have to factor in the cost of changing 12v appliances to 24 or 48v, plus 12 volt converters when needed to run lower power 12 volt systems like water pumps or the radio. It would probably cost more to change all that than the cost of upgrading a few cables and keeping it all as 12 volts.
Yes, there is some bad system design there. Undersized cables with a very high amp load!. No one to blame there but the installer! Properly size battery cables for the loads is simple. there are apps you can download on your phone to calculate the correct wire sizes
Haha well that installer would be me! :D The old orange cables were what linked the two original AGM batteries, but when I first installed the inverter I supplied that thinner red cable I had from an old 1200W inverter. As I had AGM batteries I was only drawing small loads from the inverter for some time, but having just changed to lithium I was able to load the inverter right up for the first time, which is when this problem first presented itself.
cca cables should not be used.
I don't think these are CCA cables? What made you think that? I would certainly agree in principle with what you're saying if they were.
For anyone else reading this, CCA stands for copper clad aluminium, which is copper on the outside but cheaper aluminium the rest of the way through.
You’re not the first and you won’t be the last. I’m a technician by training and you would rightly assume that I knew what I was doing. But alas no! 12 volt seems safe but start talking in terms of 100, 200, 300 amps and things can get very nasty very quickly. A very similar mistake to yours in fact. Overestimating cable size is a real trap!
Thanks for the comfort! Yep I'm a tech by trade too and the simplicity of the swap meant it just didn't occur to me. But as you say at those levels of current, all sorts of innocuous conductors suddenly turn into bar radiators!!
@@TheMusingGreg I’ve literally just upgraded my very small caravan to the same system as you, except one more battery. 360 amps worth and the 3kw inverter. I used a 20mm x 6mm busbar between batteries in parallel and they actually changed colour!! Yikes! Great channel Greg you should post more often.
Wow that's scary! Glad you're liking the channel, yeah I'd like to post more often and I've actually got the content for a number of videos all recorded, but it just takes so long (as in, numerous full days back to back) to pull all the different clips together into a decent video! So everything else including work has to go on hold while that's happening. I think in some respects I may have set myself unrealistic expectations with those really long solar blanket reviews which took weeks of solid work to produce, but don't want to follow them up with half-baked content! I've definitely got the iTechWorld battery review coming, and Hard Korr has sent me an updated version of the blanket I reviewed last year to look at, so hopefully they'll be done before too much longer!
@@TheMusingGreg Hey Greg I can’t for the life of me find that chart on that website you mentioned. Got a link? Thanks
Sorry I meant to add in the link in the description! Just done that but here it is again: www.solar4rvs.com.au/buying/buyer-guides/ultimate-dc-cable-sizing-system-calculator-for-rvs/