Size of inverter needed

capitanojuliano · January 2016

What size pure-sign-wave 12 volt inverter to run
10 laptop computers
3 Desktop Computers
3 Floor standing domestic fans
1 Internet Router
and 10 x 5 watt LED lights

Photowhit · January 2016

Too many variables, Desktops can run 150-1500 watts, floor fans 50-300+, Laptops from 25-200+

mike95490 · January 2016

It's going to be too large for a 12V system, Start looking at 24V gear

Mountain Don · January 2016

I don't mean to sound like a smartass but I would start by adding up the watts that are usually listed on the device power block or name plate.

BB. · January 2016

Get a Kill-a-Watt type meter... They should be pretty common now almost anywhere for your power needs (120/230/50hz/60hz).

http://www.solar-electric.com/kiacpomome.html

And you will want to conserve as much power as possible--Especially if you are looking at solar power.

However, that does raise the question--Is this going to be a UPS type system instead (AC mains -> battery bank -> AC inverter) used to provide power for ~4 hours per day during afternoon blackouts?

-Bill

capitanojuliano · January 2016

Yes you are right, this set-up is going to be charged by a mains battery charger and is a back-up system when there is a power outage. The frequency is such that probably even a 10 amp charger has enough time to re-coup the batteries.

BB. · January 2016

In general, I would suggest that you look at a 5% minimum rate of charge for the battery bank (if using AGM or GEL).

And, you have to decide on the type of batteries you want to use... If your power outages are rare, then a "float service" battery type (used for UPS systems) would be a better choice... The downside that these batteries, if cycled deeply, will not have very good cycle life. From my limited experience, I would suggest replacing batteries of this type (typically GEL and AGM) every two years, or after a couple of deep cycle events.

Note, when designing a solar power system, we suggest using ~1/4 of the battery bank's power per day... For a UPS system, the banks are designed to support the systems for ~15 minutes, so the battery bank may have 30 minute capacity (C*2 discharge rate).

This keeps your battery bank "small" and relatively cheap to replace every 2 years (for reliability).

If, however, you have "scheduled" power failures every weekday afternoon, you are probably better off designing this as we would for an off grid system. Design the battery bank to meet both conditions:

8-20 hour discharge rate (nominal battery bank current draw).
Maximum draw on battery bank 5 hour discharge rate (minutes to 1 hour). And 2.5 hour maximum draw rate for surge current (seconds, starting water pump, fans, etc.).
25% to 50% draw of battery bank capacity for "afternoon power failure" (battery bank should be 2-4x daily use AH capacity).
Suggest 10% rate of charge--Deep cycle batteries may do better with >5% rate of charge.

If you are looking to "ride through" power outages... Make sure your Internet service is capable of doing that too (battery/generator backed ISP connection). In the US, is is really unclear if cable/DSL connections have battery bank up at all, or if the backup would last more than a few hours.

And there is always the question about long term power outages (days)--Solar/fuel based genset, etc...

-Bill

capitanojuliano · January 2016

I shall be posing a new question which is an expansion of the previous topic.
Unfortunately it will seem even more unspecific as to exact consumption.
I thank you for your input thus far which is helping toward my provision of power in Cambodia.

South Africa · January 2016

Having been through power failures last year, here is a quick summary of what you may need for a UPS:
10 laptop computers - average of 100w = 1000w
3 Desktop Computers - average them on 250w = 750w
3 Floor standing domestic fans - average 50w = 150w
1 Internet Router - negligible
and 10 x 5 watt LED lights - 50w
Total +-2000w

You do not want to run inverter at 100%, and users are going to add more stuff, so start at a 3000w pure sine wave inverter.
Then to calc how many batteries you need: How long do you want to power the load for?
Make SURE you take into consideration that you do NOT want to drain the batteries below 50% DOD.
Now that you know how many batteries AH you need, decided 48v or 24v for the inverter, for it impacts on battery costs.

Type of batteries, I want to add to Bill posts, is that UPS inverters are not too clever with charging batts, generally speaking.
So do not go for the expensive deep cycle solar batteries. 99% of the time batteries in UPS'es are just sitting there.
Get maintenance free 'deep cycle' batteries. They last about 2-4 years depending on usage, but must NEVER be drained, ever, below 50% DOD.

Size of inverter needed

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