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12v vs. 24v vs. 48v

K

kerry wise

Jan 1, 1970
0
What are the pros/cons of the various voltages? What is the most commonly
used voltage?
 
P

philo

Jan 1, 1970
0
kerry wise said:
What are the pros/cons of the various voltages? What is the most commonly
used voltage?


for the same amount of power...the higher the voltage
the lower the current.

since you can get a lot of loss on a long cable run...
the higher voltage is desirable.
 
B

Bughunter

Jan 1, 1970
0
While lower current, and the ability to reduce conductor size is the
compelling advantage of higher nominal voltage, one downside is the higher
incremental cost of modular additions.

If you had a 12v system, you can add a single panel or battery at a time,
but with a 48v system you have to add in multiples of 4 (12v nominal)
batteries or panels at a time. Since you don't do that very often, the lower
current advantage still outweighs this 'con'.

Some of this also depends on how big a thing you are powering. 12v might be
fine for a small RV, or single appliance application especially of you plan
on using some dc appliances. 12v RV type inverters are dirt cheap these
days. Higher voltage, where you have longer wire runs such as in a house
probably preferable. 24v might be a good intermediate compromise for a small
camp.

My RV runs on 12v, my house on 48v.

Having some choice is a "good thing".
 
G

George Ghio

Jan 1, 1970
0
kerry wise said:
What are the pros/cons of the various voltages? What is the most commonly
used voltage?

The rule of thumb is:

0 - 1000 Wh 12V
1000 - 3000 Wh 24V
3000 Wh+ - 48V

Mind you these can and will overlap quite a lot.
 
G

Glenn jacobs

Jan 1, 1970
0
What are the pros/cons of the various voltages? What is the most commonly
used voltage?

One isssue with a 48 VDC system is that charging voltages exceed 48 Vdc
which means that the cable from your panels may have to be Underwriters Lab
approved, which will increase the cost. That is primarily why I went with
24, I have a fairly long run from my panels and the wire cost difference
would have been significant. You would have to have more batteries in
series, assuming you are using lead acid.

jake
 
W

Winston Smith

Jan 1, 1970
0
One isssue with a 48 VDC system is that charging voltages exceed 48 Vdc
which means that the cable from your panels may have to be Underwriters Lab
approved, which will increase the cost. That is primarily why I went with
24, I have a fairly long run from my panels and the wire cost difference
would have been significant.

Even considering you need a smaller gauge for the lower current?
 
P

Paul Blyth

Jan 1, 1970
0
Bughunter said:
While lower current, and the ability to reduce conductor size is the
compelling advantage of higher nominal voltage, one downside is the higher
incremental cost of modular additions.

If you had a 12v system, you can add a single panel or battery at a time,
but with a 48v system you have to add in multiples of 4 (12v nominal)
batteries or panels at a time. Since you don't do that very often, the lower
current advantage still outweighs this 'con'.

Some of this also depends on how big a thing you are powering. 12v might be
fine for a small RV, or single appliance application especially of you plan
on using some dc appliances. 12v RV type inverters are dirt cheap these
days. Higher voltage, where you have longer wire runs such as in a house
probably preferable. 24v might be a good intermediate compromise for a small
camp.

My RV runs on 12v, my house on 48v.

Having some choice is a "good thing".

Hi to all, this is my first post to this group.

Another advantage of 12v is efficiency. Plenty of household devices are
now available as 12vdc and you're much better off running them direct
rather than via an inverter. I know some of you will quote that you
have a 90%+ efficient inverter but that's not the whole story. You're
super-efficient inverter is only that efficient at full load, it can be
as low as 40% efficient at partial loads, (go look for the efficiency
graph in your documentation). That's one power loss straight away,
another is the mains voltage AC step down converters used to provide the
12vdc that the device needs. These can easily have an efficiency of
only 50%! So if you plugged that 12vdc LCD TV which draws 30w into it's
psu and measured it's draw at the mains voltage end, well mine draws 45w
instead. Add that in with an inverter running at a generous 75%
efficiency partial load and you're looking at drawing around 56w for a
device that should draw 30w. In this example that means twice as much
generating capacity, twice as much battery backup, twice as much money
to power that device.

This applies to all you people with low voltage systems who're running
lights from an inverter too. If you want to optimise your system and
it's run times then go low voltage as much as possible. It's pretty
easy to get to a stage where you can even get rid of the inverter's own
power draw by turning it off most of the time! You only need to turn it
on to run anything with a large motor in it, and most household
appliances which use a large motor are available in super-efficient DC
versions. I realise people may say that super-efficient DC appliances
are much more expensive, in my experience it's even more expensive to
provide the power generation capacity for the non-DC devices, whether
they are efficient or not. This cost factor does depend somewhat on the
irradiation of your location though.

Apologies for ignoring the 24v and 48v options.
 
H

Hank McCall

Jan 1, 1970
0
Paul said:
Hi to all, this is my first post to this group.

Another advantage of 12v is efficiency. Plenty of household devices are
now available as 12vdc and you're much better off running them direct
rather than via an inverter. I know some of you will quote that you
have a 90%+ efficient inverter but that's not the whole story. You're
super-efficient inverter is only that efficient at full load, it can be
as low as 40% efficient at partial loads, (go look for the efficiency
graph in your documentation). That's one power loss straight away,
another is the mains voltage AC step down converters used to provide the
12vdc that the device needs. These can easily have an efficiency of
only 50%! So if you plugged that 12vdc LCD TV which draws 30w into it's
psu and measured it's draw at the mains voltage end, well mine draws 45w
instead. Add that in with an inverter running at a generous 75%
efficiency partial load and you're looking at drawing around 56w for a
device that should draw 30w. In this example that means twice as much
generating capacity, twice as much battery backup, twice as much money
to power that device.

This applies to all you people with low voltage systems who're running
lights from an inverter too. If you want to optimise your system and
it's run times then go low voltage as much as possible. It's pretty
easy to get to a stage where you can even get rid of the inverter's own
power draw by turning it off most of the time! You only need to turn it
on to run anything with a large motor in it, and most household
appliances which use a large motor are available in super-efficient DC
versions. I realise people may say that super-efficient DC appliances
are much more expensive, in my experience it's even more expensive to
provide the power generation capacity for the non-DC devices, whether
they are efficient or not. This cost factor does depend somewhat on the
irradiation of your location though.

Apologies for ignoring the 24v and 48v options.
where do you get "mains to 12V converter @ 50%" ? a switching conveter
should be 70 to 90%, a big iron transformer & diode job 80-90%
 
G

Gymn Bob

Jan 1, 1970
0
One transformer winding plant I worked in made 6 volt bulb pilot lamp
assemblies complete with a 120/6v mini transformer in the 2B panel mounted
assembly. The primary current was higher than the bulb consumed at 6vac.
Smaller transformers are less efficient than large ones with lots of iron.
 
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