48 Volt System

[Adelie]

Originally Posted by GrowleyMonster

I always thought the cutoff was 50v nominal.

.......

Turns out that we are both right but you are much more right than I am.

Within the US there is a split between 50v & 60v being the cutoff for DC depending on the particular code with 50v being more common. (30v AC)
Even the 60v is supposed to be dry conditions, ripple free.

The fire code says 15vDC for wet or rippled current. 6v for AC.

The International Electrotechnical Commission (IEC) and the UK put the limits for Extra-low voltage at 50v AC or 120v DC (ripple free).

[team karst]

Even the IEC has various voltages, depending on wet/dry and type of equipment. Anyone have the spec for rec boats?

[skipperpete]

I had a 32volt system in a past boat and dropped it to 24v mostly because it was difficult to source 32 volt pumps and light globes. I seem to be sensitive to low voltage DC electric shocks possibly because I live and work in the tropics with a lot of perspiration happening and usually small cuts and abrasions. I get a real jolt from 32V , about the same from 24 and an annoying shock from 12v so for me a 48 volt system would be out of the question.
On a bit of a tangent, I just got an email from my marina office informing me that they had 2 fires over a couple of days that destroyed the very large capitainerie, first was a big fire that started in the solar array on the rooftop which was put out by the local sapeurs pompiers and then 2 days later another fire in the remaining panels that finished the roof off completely. All power was off to the building and the weather is cold. Does anyone have any experience with actual solar panel fires? And might a 48volt system be more likely to torch the array?

[SOLAR SUPPORT]

Originally Posted by skipperpete

I had a 32volt system in a past boat and dropped it to 24v mostly because it was difficult to source 32 volt pumps and light globes. I seem to be sensitive to low voltage DC electric shocks possibly because I live and work in the tropics with a lot of perspiration happening and usually small cuts and abrasions. I get a real jolt from 32V , about the same from 24 and an annoying shock from 12v so for me a 48 volt system would be out of the question.
On a bit of a tangent, I just got an email from my marina office informing me that they had 2 fires over a couple of days that destroyed the very large capitainerie, first was a big fire that started in the solar array on the rooftop which was put out by the local sapeurs pompiers and then 2 days later another fire in the remaining panels that finished the roof off completely. All power was off to the building and the weather is cold. Does anyone have any experience with actual solar panel fires? And might a 48volt system be more likely to torch the array?

You may be sensitive to electricity. Wet ground, humidity is also known to increase the effect of warping. In terrestrial solar energy systems, the voltage between the solar panels can go up to 1000V. The voltage of the system is the level at which the regulator lowers this voltage.

Incorrectly calculated cable cross-sections or insufficient maximum voltage value of the charge regulator are the main causes of this and similar accidents. Generally, when the weather is very cold and the sun's rays are strong, the performance of the system increases very much.

The reason for this is that the cell voltage increases by a certain amount for each degree below 25°C in pv cells. When the temperature of the Pv cells rises above 25°C, the cell efficiency decreases. The Wp value written on the solar panel labels can only be approached in such very cold weather and when the sun rays are strong. In case the air temperature drops below 0C°, the cell temperature may decrease below 25°C.

If the system is designed by taking into account the possibility of experiencing these conditions, the cooling air will not cause any problems in the system. A system voltage of 48 volts is a fairly normal level for off-grid installations.

[team karst]

Originally Posted by SOLAR SUPPORT

... A system voltage of 48 volts is a fairly normal level for off-grid installations.

Curiously, large solar arrays are running just above 1kV.
At least the 75MW arrays I have been working around.

[s/v Jedi]

Originally Posted by team karst

Curiously, large solar arrays are running just above 1kV.
At least the 75MW arrays I have been working around.

I think he means battery voltage, not solar array voltage. Victron sells higher voltage units, here is one for up to 450V solar arrays but it’s 48V battery: https://www.victronenergy.com/invert...rs-smart-solar

[GrowleyMonster]

Originally Posted by skipperpete

I had a 32volt system in a past boat and dropped it to 24v mostly because it was difficult to source 32 volt pumps and light globes. I seem to be sensitive to low voltage DC electric shocks possibly because I live and work in the tropics with a lot of perspiration happening and usually small cuts and abrasions. I get a real jolt from 32V , about the same from 24 and an annoying shock from 12v so for me a 48 volt system would be out of the question.
On a bit of a tangent, I just got an email from my marina office informing me that they had 2 fires over a couple of days that destroyed the very large capitainerie, first was a big fire that started in the solar array on the rooftop which was put out by the local sapeurs pompiers and then 2 days later another fire in the remaining panels that finished the roof off completely. All power was off to the building and the weather is cold. Does anyone have any experience with actual solar panel fires? And might a 48volt system be more likely to torch the array?

Back in the day, Gulf of Mexico shrimp boats used a 32VDC system, and some other vessels in other fisheries, too. There were a lot of electrical goods available and maybe still are, if you look to a fisherman's chandlery rather than a yacht chandlery. Chest freezers and refrigerators, potable water pumps, electric bilge pumps, lights and incandescent light bulbs, fans, (very good ones, too!) and of course 32v electric starter for the engine. Even the old Wood Freeman hunting type autopilots that ran off a flat top magnetic compass. Radar. Fathometer, especially the stylus type that uses a roll of special paper and burned the mark with the electrically charged stylus. Many AC equipped boats still use the 32VDC system for some things, particularly engine starting or for fans and lights in the house, for when the 120VAC plant is shut down. I always wondered why 32V and not 36V. I guess electric golf carts and 6V golf cart batteries weren't really a thing back in the 70's. Many trucks, buses, and heavy equipment used the 8v X 4 system,

[RaymondR]

Originally Posted by s/v Jedi

I think he means battery voltage, not solar array voltage. Victron sells higher voltage units, here is one for up to 450V solar arrays but it’s 48V battery: https://www.victronenergy.com/invert...rs-smart-solar

My guess would be that the promoters of large solar arrays, like the power line folks before them, have discovered that running high volts instead of high amps keeps the outlays on copper down.

My prediction is that now that solar systems become more ubiquitous a greater availability of higher voltage DC storage and generation systems will come available for us boating folks to exploit.

Switch mode power conversion systems are dirt cheap and everywhere these days, hardly a transformer and diode rectifier system in sight anymore, and as lithium, with it's high current acceptance capability, replaces lead more higher voltage storage and charging systems will come into use.

[SOLAR SUPPORT]

It should be noted that the cost advantages that come with increasing voltage levels of batteries, energy converters and power transmission infrastructure are not limited to the reduction in cable cross-sections.

The costs of devices such as solar charge controllers, inverters, ac-dc chargers and electrical control equipment also decrease as the system voltage increases. This is what I am trying to convey. It's definitely not a discovery.

[s/v Jedi]

Originally Posted by SOLAR SUPPORT

It should be noted that the cost advantages that come with increasing voltage levels of batteries, energy converters and power transmission infrastructure are not limited to the reduction in cable cross-sections.

The costs of devices such as solar charge controllers, inverters, ac-dc chargers and electrical control equipment also decrease as the system voltage increases. This is what I am trying to convey. It's definitely not a discovery.

Exactly, take a Victron MPPT controller. Those are rated for charge current output. This means that they double in power when you go from 12V to 24V and they quadruple in power when you go from 12V to 48V. And the price difference is significant!

There’s more: voltage drop allowance is a percentage of the voltage. Important circuits must stay within 3% voltage drop, which for 12V is 0.36V but for 24V it becomes 0.72V and for 48V it’s even 1.44V.
But this voltage drop is the result of the current times the resistance of the wire. This all adds up to enormous differences.

Let’s say we have a circuit with 1 Ohm resistance. How much power can we put through this circuit while staying in a 3% voltage drop?

For 12V: allowable drop is 0.36V. This means a maximum current of 0.36 / 1 = 0.36A. So the maximum load is 12 x 0.36 = 4.32W

For 24V: drop 0.72V, current 0.72A, max load 24 x 0.72 = 17.28W

For 48V: drop 1.44V, current 1.44A, max load 48 x 1.44 = 69.12W

So the difference is squared: When you double the voltage, you can supply 4 times as much power and when you go from 12V to 48V then you can supply 16 times as much power through the same circuit!

[RaymondR]

Great post Jedi, got straight to the guts of the matter in easily understood terms.

[s/v Jedi]

Originally Posted by RaymondR

Great post Jedi, got straight to the guts of the matter in easily understood terms.

Thanks, I surprised myself keeping it so compact and easy

[Adelie]

Originally Posted by team karst

Curiously, large solar arrays are running just above 1kV.

At least the 75MW arrays I have been working around.

Well when I get the point that I have 250kW or so of panels installed on my boat then I’ll have a look at going with higher voltage panels.

[Adelie]

Originally Posted by s/v Jedi

Exactly, take a Victron MPPT controller. Those are rated for charge current output. This means that they double in power when you go from 12V to 24V and they quadruple in power when you go from 12V to 48V. And the price difference is significant!



There’s more: voltage drop allowance is a percentage of the voltage. Important circuits must stay within 3% voltage drop, which for 12V is 0.36V but for 24V it becomes 0.72V and for 48V it’s even 1.44V.

But this voltage drop is the result of the current times the resistance of the wire. This all adds up to enormous differences.



Let’s say we have a circuit with 1 Ohm resistance. How much power can we put through this circuit while staying in a 3% voltage drop?



For 12V: allowable drop is 0.36V. This means a maximum current of 0.36 / 1 = 0.36A. So the maximum load is 12 x 0.36 = 4.32W



For 24V: drop 0.72V, current 0.72A, max load 24 x 0.72 = 17.28W



For 48V: drop 1.44V, current 1.44A, max load 48 x 1.44 = 69.12W



So the difference is squared: When you double the voltage, you can supply 4 times as much power and when you go from 12V to 48V then you can supply 16 times as much power through the same circuit!

That also means that 4x the heat is being generated in smaller wires.

[SOLAR SUPPORT]

To understand the cost reductions that come with rising system voltage, you should focus on the electrical power formula. In general terms, Power is physical work done per unit time or energy converted per unit time. P = work/time = U x I

To give an example: A small windlass needs an electric motor with 700-1000 watts in order to be able to pull the chain and the anchor attached to the end of a certain length to the boat without difficulty within the desired time. Continuing with this example: Electric power through a conductor: It is calculated with the formula P=UxI. You must supply the power required by the windlass with the voltage suitable for the structure of the motor on it.

If the motor works with 12 volts: you will find the upper value of the current to be transmitted over the cable for the power you need to transmit from the battery to the motor: 1000W/12V = 83.3A.

If the windlass has a motor suitable for 48 volts with the same power, it is possible to transmit the same power with 20.8A current by using 48 volt batteries. This means you can use a cable with a thinner cross section up to 1/4 compared to 12 volts.