Solving for voltage drop over 200'

[jbatx]

Hey all, I need some advice on solving a voltage drop issue that has emerged due to some planning and provisioning mistakes which I made.

The layout...

Shipping container has my batteries, scc, inverter and the array is just out side the container.

21.1 kwh lifepo total capacity
5kw 120v inverter
5kw array

The cabin with all the big loads is about 200' away.

The geography and future development plan forced the distance. The mistake was running 120v over 10/3 solid copper for the main line from the inverter to the main cut-off and breaker box.

Originally the load was going to be no more than about 10a. I should have gone with a higher awg and 240 from the start. But, alas, I didn't.

The Inverter has been upgraded from 3kw to 5kw and the peak load now is about 25 amps over that 120v 200' run now that the cabin has a new induction cook top, electric kettle, fridge, and mrcool minisplit.

Some guests use everything at once because they don't like to read... I guess.

Bottom line is that lights dim a lot when the induction cooker kicks on. They dim less when the heat is on. I need to reduce the voltage drop somehow.

I have considered...

1. Split phase 240v with a sungold 4kw inverter - replacing my current 5kw 120v. Then splitting the two big loads onto different 120 lines.

2. Sending 240v from a new 240v single phase inverter to a 4kw step down transformer and 120v into the breaker box as it's currently wired.

Running bigger awg wire is not an option due to geography, hassle and cost of trying to get expensive bigger wire through 2" conduit with curves that contains existing wire. Heck, the wire would cost hundreds alone.

What would you do ?

 

[Hedges]

Transformers?

120V to 480V (+/-240V center tap grounded)
Back to 120V at far end.

4x the voltage, 1/4 the current, 1/16th the power loss

 

[camelCase]

Low voltage lighting? Install switching that only allows one major appliance to run at a time? i.e. if you want to run the induction cook top, then you have to flip a switch that turns off the mini-split? Take the electric kettle out of the unit and put in a cook top one so they can't double up on the power usage for cooking?

For the 240v option, I my preference would be option one and rewire the breaker panel with a standard service panel that splits the 240 into separate 120 legs.

 

[jbatx]

Transformers?

120V to 480V (+/-240V center tap grounded)
Back to 120V at far end.

4x the voltage, 1/4 the current, 1/16th the power loss

Good idea. 480 scares me. I'd feel more comfortable going just to 240v. 12.5a at 240 over 230' has a drop of 2.5%, which is acceptable.

Would this work?

ROCKSTONE POWER 5000 Watt Voltage Converter Transformer - Heavy Duty Step Up/Down AC 110V/120V/220V/240V Power Converter - Circuit Breaker Protection – DC 5V USB Port - CE Certified [3-Year Warranty] https://www.amazon.com/dp/B00J0CF8W...abc_V57Q861D1TBQZQKHKMFS?_encoding=UTF8&psc=1

 

[MichaelK]

To me, installing an all-electric stove in a solar-only dwelling is just begging for failure. I'd recommend pulling the stove and replacing it with a propane model.

You could install a tank near the container and just run plastic gas pipe from the container to the cabin. To do mine, I rented a trencher, and cut the 130' of 18" deep trench before lunchtime. I just installed Tees in the line for the kitchen stove and the utility room hot water heater.

I'm very happy with the new gas stove I just installed last year. All I needed to do was screw in the correct orifices for propane instead of natural gas.

 

[diyernh]

Could you move some batteries and the inverter into the dwelling? Leaving the slow, but steady charging from solar over the the long wire? The high current draw could happen quickly with the batteries and inverter inside, slowly recharging from any remaining batteries and solar in the container.

 

[Bluedog225]

Lots of good ideas here. I agree the cooktop presents some issues.

 

[Brandon8792]

Depending how big of an induction cooktop you could be screwed on that size of inverter.

A full size stove alone can pull 12,000 watts, maxing out a 12kw inverter without any other loads… even if it’s a dual cooktop, one is probably a 3000 watt, and the other 1800w… that along with the heat and air, or anything else is still begging for trouble.

For anything that’s going to last, I wouldn’t want to push it more than 80% of its peak power at anytime, and 50% would guarantee a long life. Just my suggestion from my 12kw off grid inverter setup… and I’m still wanting to do some form of soft start of super capacitor system to hold off startup loads on the ac side to not be as forceful on the inverter

 

[jbatx]

It's a single burner duxtop commercial unit. Little thing. It's staying put. 1800w max.

https://www.amazon.com/dp/B07G9YKPQ...abc_101BVYK7W9F6XBG94981?_encoding=UTF8&psc=1

 

[jbatx]

Could you move some batteries and the inverter into the dwelling? Leaving the slow, but steady charging from solar over the the long wire? The high current draw could happen quickly with the batteries and inverter inside, slowly recharging from any remaining batteries and solar in the container.

I considered that early on in the project. The shipping container was chosen because it can house the power and water out of the elements and away from flammable stuff like the suites ...which I call cabins, But are actually large insulated safari tents. There's no place to safely put the electrical and batteries at the big tent.

Oh, the container is where it is because it's central point on rhe property and distributes too all the tents. It was also physically impossible to get it any closer to rhe tent's plateau.. I mean unless I wanted to rent a big ass crane.. no. There is only one tent now. There will be three. Obviously when that time comes, larger and/or multiple inverters will be needed.

Also, the shipping container has a larger cantilevered roof on a 3.5% slope to catch a lot of rain. The roof cover the container and the two 5400g rain tanks. All of that and the trees keep the container in the shade all day. So, it doesn't get very hot in there, even in the summer.

 

[jbatx]

I think the best solution given all the factors is to step up to 240 then back down to 120. I just need to select the right transformers

 

[Hedges]

Good idea. 480 scares me. I'd feel more comfortable going just to 240v. 12.5a at 240 over 230' has a drop of 2.5%, which is acceptable.

480V center tapped is just 240V, same as the British use. So long as you don't grab both hots at once.
Typical wire used in conduit, or UF, has 600V insulation so could carry as much as +/-600V (not sure if that is peak or RMS, but +/-240Vrms is way under)

Would this work?

ROCKSTONE POWER 5000 Watt Voltage Converter Transformer - Heavy Duty Step Up/Down AC 110V/120V/220V/240V Power Converter - Circuit Breaker Protection – DC 5V USB Port - CE Certified [3-Year Warranty] https://www.amazon.com/dp/B00J0CF8W...abc_V57Q861D1TBQZQKHKMFS?_encoding=UTF8&psc=1

At 26 lbs, is that thing really 5000W?
It says to avoid using over 3500W, and you've got a 5000W inverter.

Here's an example 5kVA (isolation) transformer. 75 lbs.

https://www.grainger.com/ec/pdf/4WUD9_1.pdf

Non-isolating transformer would be half the weight, 37 lbs. (compared to 26 lbs, pretty close to 5000 VA vs. 3500 VA)

 

[Bluedog225]

Give some thought to transformer hum.

 

[jbatx]

Give some thought to transformer hum.

Good point. I don't know when hum becomes a side effect. That'd be a bad thing out here. It's middle of nowhere quiet out there.

 

[Hedges]

My preferred approach is used higher voltage DC (up to 600 Voc) from PV over the distance, keep AC wiring shorter.
Benefit is that SCC can tolerate the drop, it is only lost power. Surge for motors, or heavy loads, is over the short AC wiring.
One disadvantage is that power peaks during a short part of the day, could be more total loss. But maybe not with significantly higher voltage.

My system has 100' or 150' to some strings, each routed in 12 awg. During average weather, Voc is 480V and Vmp is 380V. So 3x your 120Vrms, for 1/9th the loss.

I have 6 awg running 150' from inverter back to the house. (other loads are local.) I do notice incandescent lights dimming when loads turn on. LED doesn't.

Considering the price I saw for quality 120/240V transformers, unless you find a used deal, a split-phase inverter and distributing loads across the two phases could be better. Also add a small balancing transformer, to help with extra loads on one phase.

 

[acdoctor]

It may be late and my brain maybe tired but making 120 to 240 split phase doesn’t increase the voltage on any current carrying conductors. If you have extra conductors to add the other phase just parallel. Might even get by using the equipment ground driving a rod at the far end. 2 inch conduit is larger enough for 4 4/0 conductors to fit. It should not have more than 270 deg. Of bend with out a pull box.

 

[Hedges]

It may be late and my brain maybe tired but making 120 to 240 split phase doesn’t increase the voltage on any current carrying conductors. If you have extra conductors to add the other phase just parallel.

Only if loads on each phase cut in half, the rest redistributed to other phase.
But you could get several loads on one, none on the other.
So you're right. Instead of 3-wire 120/240V, if you did 4-wire two for line, two for neutral, that could be better. Or larger gauge.
Only doing 240V loads, or 240V transmission by means of transformer and stepped back down to 120V, saves copper. 2-wire transmission at high voltage is best.

 

[Smokin]

Load sequencer!!!!!!

 

[mikejoconnor]

Currently you are getting 10v / 8.7% of resistance loss. If you moved the inverter to the dwelling, and ran ~450v from your PV array to the inverter, you would be running closer to 10-12 amps on the long run instead of 25. That would drop your resistance loss to under 6v / 1.3%.

You may need to swap to a different charge controller, but for a long run it's a reasonable solution.

 

[jbatx]

My preferred approach is used higher voltage DC (up to 600 Voc) from PV over the distance, keep AC wiring shorter.
Benefit is that SCC can tolerate the drop, it is only lost power. Surge for motors, or heavy loads, is over the short AC wiring.
One disadvantage is that power peaks during a short part of the day, could be more total loss. But maybe not with significantly higher voltage.

My system has 100' or 150' to some strings, each routed in 12 awg. During average weather, Voc is 480V and Vmp is 380V. So 3x your 120Vrms, for 1/9th the loss.

I have 6 awg running 150' from inverter back to the house. (other loads are local.) I do notice incandescent lights dimming when loads turn on. LED doesn't.

Considering the price I saw for quality 120/240V transformers, unless you find a used deal, a split-phase inverter and distributing loads across the two phases could be better. Also add a small balancing transformer, to help with extra loads on one phase.

I think I agree about the spit phase approach ...after doing more research and finding real world prices.

A sungold 6kw split phase is 1199 right now. Where as two transformers will likely run me 1500. ...and add two more parts into the system.

I spoke to my contractor and he feels confident in our ability to run another set of conductors. Those would give us 2x 10awg solid copper. Or bigger