So, 60Vdc parts. Where are y'all getting them?

[TaliaDPerkins]

I am trying for an all electric bus to the greatest degree possible.

I have 6400W of solar, and a 4p16s LiFePo4 battery set @ 304AH/cell, 2 of EG4 6kXp inverters for 220Vac HVAC & general house 120vac, and 3 of 4kW 48vdc nominal (60Vdc limit) to 230VAC for kitchen appliances, backup for the mini split, etc. If every inverter was maxed out in a worst case scenario, I would be pulling close to 970A from the batteries at 50.5Vdc at the combined battery busbar.

I have conceded there is likely weather for which I will have no hot water, no non-frozen water and tanks, and no house heat unless I use propane or diesel, and since I already was getting a diesel coolant heater -- I'll be using that for hydronic floor heat if the mini split can't keep up. Next back up is the diesel air heater -- at the penultimate extremity I would try to run the engine to keep the hydronic heating up. As an ultimate "I don't want to die here tonight", backup, I could rig a hot tent camping stove through a window. Yes, the windows are deleted. Yes, the RV windows are double glazed. Why yes, I plan on visiting Alaska, for a while, and not freezing.

I have avoided propane successfully as a house utility, and have two questions.



Aluminum 500/400MCM power cabling, has any one ever used it? Does a 16ton hydraulic crimper and the dies for such sound like it will get it done to make safe connections? Yes, I know to use Penetrox wherever AL touches Cu. The Al cabling cost is like $600, the Cu cabling cost is like $1700. I am taking a buy once, cry once philosophy to my roving forever home -- but if I can avoid throwing money away I will.

16T Hydraulic Crimping Tool 8 AWG to 600 MCM Battery Cable Crimping Tool 0.87 inch Stroke Hydraulic Lug Crimper Electrical Terminal Crimper with 13 Pairs of Dies

https://www.amazon.com/dp/B0BCFG9BFS?smid=A15RXF8WAZUON9&ref_=chk_typ_imgToDp&th=1

This seems like the correct thing to me. I am asking for a reality check -- for that and for Aluminum cabling generally.

2nd topic. I have sourced fusing for my needs. It's not even expensive. What is turning out to be near impossible to get are 60VDC (or better) rated battery disconnect switches with continuous running current in the range I anticipate, which could well be 300A day to day, and 400A even with no inverter in surge mode if I am cooking and the lights are on and the HVAC pulls in. And since fusing is sized for surge mode, worst case is that a switch may have to interrupt that ~970A @ 50.5Vdc or ~870A @ 55.2Vdc depending on state of charge in a fault event.


Where are are people with 48VDC nominal systems getting components? 16 LiFePo4 cells in a string is 51.2VDC nominally. 100% SoC is 58.4Vdc. Most of the DC vehicle switching stuff I see tops out at 32VDC, or, is not for vehicles and is topping out at 100, 500, or 1kVDC, and items with the latter ratings are large and very $$$.


[Edit: I know I'll edit this, I'll find typos.]

 

[AlphaHare]

I personally wouldn't use aluminum cable in an RV application. Could you do it with buss bars?

FWIW - the RVIA Low Voltage (<60 VDC) standard does not have aluminum as an option, copper only to SAE J1127 and J1128 (welding cable and stranded cable).

 

[TaliaDPerkins]

Copper at all is $$$

And busbar $1k more than Cu cabling.



And busbar is generally more $ to have it insulated.


Al insulated cable at THHN or THHX I can zip tie/wire harness to where it won't vibrate. Chief problem with Al is the expansion/contraction with temperature changes, and, dissimilar metals corrosion. Using Al rated connectors and crimping them properly "should" resolve connector creep. The Penetrox "should" solve corrosion (that and the whole thing is protected from the environment).



In theory.


I asking here about, has anyone done it with success (or with problems)?


If no one has used Al cabling for high amperage DC in a skoolie, then I guess I get to tell people how it goes?



Not sure I put any great store by the RVIA when they used solid instead of stranded copper for 120/240vac . . . (at least Chuck Cassady said they did about 2 years ago :ermm: ). But thank you!



Chief concerns at the moment is who makes DC accessory components rated at 60 VDC and up to say 72, etc, and for amperage up to that 970A. Full load rated battery disconnects are the kind of thing that should work, but at that DC voltage they are proving to be a problem to find. BEP Marine, Blue Sea for example -- no help there yet.

 

[AlphaHare]

I like Chuck too. The RVIA follows the NEC for AC and the NFPA for most everything else - not their own codes.

I'd worry about vibration. Aluminum work hardens very easily, stranded copper does not.

 

[AlphaHare]

Another thing I just remembered from past employment....

Are you familiar with Diesel Locomotive Cable? This is about the toughest stuff anywhere for vibration and current capacity.

https://www.awcwire.com/power-cable-and-portable-cord/dlo-diesel-locomotive-cable

I know you're looking at cost, and this is still copper, but the ampacity goes off the charts.

 

[TaliaDPerkins]

Thank you AlphaHare,

That is a more economical source of tinned copper stranded than I have run into before!


My chief concern with ampacity is the conductors going from the totality of the battery bank to the rest of the system. It is very unlikely all inverters would surge at once with the batteries also low -- which circumstance plus 10% margin I think produces that maximum amp flow of 970A.


Copper has a higher brief overload capacity than does aluminum. I am weighing the relative simplicity of downsizing to at most 0000AWG, and counting on slow blow 500A fusing to permit safe handling of surges without interruption and still make open in the event of a genuine short.


I'm looking at a lot of I^2/T specs, wires as fusible links specs, and temperature rise with overload specs 'til my eyeballs bleed.

 

[Mercuric Mind]

For power equipment you can check out this place. https://www.rinconpower.com/products
Or look into power controls for EV applications.

 

[TaliaDPerkins]

Thank you, still $800 per, but better that I have seen.

 

[TaliaDPerkins]

What is to be done?

I hate to belabor a point or a question uselessly, however.


DC voltages in RV/skoolie solar systems will only climb as efficiency and lower losses are sought.


24VDC is an effective minimum for vehicles bigger than trailers and vans and truck bed campers. Systems are going for 36V, 48V, and 60 & 72VDC.


MPPT charger input are going for 100 VDC & 160 VDC minimums and 400& 500/600 VDC maximums.


It seems vehicular switchgear is not keeping up.

 

[Kentucky Dreaming]

My truck camper works great on 12 volts DC. But the walls are falling apart from water damage.

 

[AlphaHare]

It seems vehicular switchgear is not keeping up.

To be fair, your full system max (50.5V @ 970A) is 48,985 Watts. That's more than my house (220v @ 200A) a 44,000 Watts.

This is the realm of bespoke system engineering. I'd guess it's going to be a long time before garden-variety vehicle electrical components get anywhere close. Can you break into independent sub-systems to reduce the individual power handling to more manageable levels?

 

[TaliaDPerkins]

Some things to consider . . .

400A panels and 240vac nominal service are not uncommon, especially as the ability to charge 1 or more electric vehicles at homes is requested. 96kw


And that is theoretically the intended everything on at once at least briefly and nothing trips capability.


What I am trying to bring to light is the inability of most DC components to switch/interrupt higher than 32VDC (a common maximum I see). DC systems in RV house storage are moving towards 48VDC -- raising voltage is the easiest way to increase power without more copper. It's simply not uncommon for the DC storage side of things to be 48VDC, and many domestic solar system are going higher.


The specific worst case I am trying to build for is the very unlikely event of all 24kw capacity in inverters being on their allowed period of overload (twice normal capacity for variously 3 to 10 seconds) and a disconnect needing to open and clear at that time. That is not a likely situation. Far more likely would be ~242A drawn when something trips.


The things is most disconnects seem not to be rated for over 32vdc.

 

[Mercuric Mind]

Some things to consider . . .

400A panels and 240vac nominal service are not uncommon, especially as the ability to charge 1 or more electric vehicles at homes is requested. 96kw


And that is theoretically the intended everything on at once at least briefly and nothing trips capability.


What I am trying to bring to light is the inability of most DC components to switch/interrupt higher than 32VDC (a common maximum I see). DC systems in RV house storage are moving towards 48VDC -- raising voltage is the easiest way to increase power without more copper. It's simply not uncommon for the DC storage side of things to be 48VDC, and many domestic solar system are going higher.


The specific worst case I am trying to build for is the very unlikely event of all 24kw capacity in inverters being on their allowed period of overload (twice normal capacity for variously 3 to 10 seconds) and a disconnect needing to open and clear at that time. That is not a likely situation. Far more likely would be ~242A drawn when something trips.


The things is most disconnects seem not to be rated for over 32vdc.

I'm not an electrical engineer but ,I believe that once the voltage gets above that 32V the arcing becomes an issue when making or breaking connections under load. This isn't an issue with AC as much because every cycle the voltage drops to 0v. So on the DC switching equipment there needs to be arc suppression to prevent contact welding. Related to contact welding, be sure to have an ability to slowly charge up any capacitors, like in an inverter, prior to closing any switch / contactor to prevent its destruction.

 

[TaliaDPerkins]

I begin to see a market for vehicular rated 100 ~ 200 VDC rated breakers and disconnects, probably with compressed air assisted arc breaking . . .

Capacitors a la snubbers for arc suppression for the amperage range involved could become prohibitively large and expensive quickly, probably better to just have the intended on purpose procedure be make and break with no load, and use active arc extinguishing for emergency breaks.

 

[Mercuric Mind]

This is along the line of what I was talking about with a pre-charge circuit to charge the capacitors in a inverter charger.https://www.youtube.com/shorts/QGqJp89hEfo Here is a schematic of the automatic system pre-charge circuit on my power system. It is a one off device my dad (retired electrical engineer) and I designed and built to prevent any contact welding on system startup. It is likely overkill. It is designed to work with control signals from the orion jr II BMS.

 

[TaliaDPerkins]

That is interesting and potentially helpful. I am chiefly concerned about the problems of disconnecting an already running maximum/shorting load on an emergency basis -- generally, I can make sure the loads are off when I go to energize the system.

Thank you!

 

[AlphaHare]

There is a huge world of equipment capable of your switching needs - this is simply in the range of power generally considered industrial controls rather than RV. Industrial controls probably won't have a UL or CSA or CE listing for RVs, but I wouldn't hesitate to use them if I dealt with possible vibration issues.

Here's a crappy one from Amazon - there are 100's like it

https://www.amazon.com/DIHOOL-Circuit-Off-Grid-Disconnect-Inverter/dp/B09P4QQMM7/?th=1

 

[TaliaDPerkins]

That is far better than many, thank you. I may well end up using that exact one. I may simply have to concede my goal of an interrupt rating for amperage which can handle an unrealistic but possible "worst case" scenario.

I particularly appreciate the 15kA rating for breaking capacity. Take that, inadvertent dead shorts!

"Here's a crappy one from Amazon - there are 100's like it" <-- And actually no, in many hours of searching that did not show up, even the series did not.