1
\$\begingroup\$

In other words, does a 1000-watt inverter, draw the same as a 500-watt inverter if they are charging only a laptop? The laptop will draw the same amount and the inverter capacity is really just that, capacity?

i.e. 1000-watt inverter CAN draw UP TO 1000-watts, and the same for 500-watt inverter.

My issue is that I plug in a 1000-watt inverter to a battery, and voltage is dropping to 12.2v. I was informed that I should keep my battery voltage, above 12.4v to keep it healthy and I worry that 12.2v constant (during full solar input) and 11.8v (at night when there is no sun) is killing my battery.

I am currently using a 1000-watt inverter, and now I'm wondering if it is overkill and need to downgrade to a 500-watt inverter to charge a laptop/run cable modem/router (~100-watts/per hour).

\$\endgroup\$
  • 1
    \$\begingroup\$ Look at the efficiency curves and do your calculation. \$\endgroup\$ – Eugene Sh. Sep 7 '16 at 16:26
  • 1
    \$\begingroup\$ Approximately, yes, they would consume the same amount of battery power. All else being equal. But some inverters are more efficient than others. And there are a lot of very poor quality inverters available on the market for some reason. Note that a 1000 Watt inverter would need to use around 100 Amps from the battery to produce a true 1000 Watts. So you would need to use very heavy cable. A lot of cheap 1000 W inverters don't even allow connections with heavy battery cable. \$\endgroup\$ – mkeith Sep 7 '16 at 16:28
0
\$\begingroup\$

If two 100% efficient inverters, one 500W max throughput, one 1000W, are used to drive the same load, they will pull the same power from the battery.

Of course neither will have 100% efficiency. Even at no output load, they will draw some power. The chances are high that the 1000W inverter would draw more idle power than the 500W, but it's not a foregone conclusion. A well designed 1000W inverter could be more frugal at no and low loads than a badly designed 500W.

For your application, rather than suffer the inefficiencies of two stages of conversion, it will be more efficient overall to use a single 12v input DC to DC laptop SMPS, and one to your router/modem, unless they are 12v input (mine are) in which case run them straight form the battery.

\$\endgroup\$
  • 1
    \$\begingroup\$ I agree with everything said except for running straight from the battery. If the battery behaves badly your devices connected directly would let out their magic smoke. Maybe use a DC-DC regulator that has a boost stage and then an LDO or buck. Not the most efficient in the world but better than using an inverter \$\endgroup\$ – Daniel V Sep 7 '16 at 17:53

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.