Amp Hours & Voltages & the Like: Leccy for the Terminally Stupid
- Thread starter Dubversion
- Start date
gentlegreen
I hummus, therefore I am ...
Those adverts are full of hype.Minnie_the_Minx said:
Every electric heater ever made is 100 percent efficient at spinning your meter.
A radiant heater may be more effective at keeping just you warm rather than the whole room. Actually, heated underwear is the most efficient option
Electric heating is wasteful because so much energy is wasted converting (gas) into electricity and getting it to you.
free spirit
more tea vicar?
ah - dammit.Dubversion said:
*short answer*
if you were drawing 500watts continuously, the invertor was 85% efficient, and you're using a bog standard car battery you'd probably get around 10 hours use out of it if the batteries were fully charged and new without either the invertor cutting out, or you damaging the batteries, though depending on the invertor you could possibly push that to 15-20 hours though if you did it regularly the battery would fuck up pretty quick.
If it's a proper deep cycle battery then you'd probably get 25-30 hours ish off it at a push again dependant upon the operating range of the invertor.
*long answer*
ok everyone above's pretty much right, though there's some stuff you need to check on your invertor instructions...
first check if the 500 watts is the average or peak output. A lot of cheap invertors list their peak output rather than their average / continuous - if it was it's peak output then that'd mean it would handle 500 watts for a short period, but it'd overheat and shut off if you tried to draw it continously. The continuous / average rating is the highest level you can run it at continuously for hours on end without it overheating and cutting out.
2nd check is what the operating voltage range of the invertor is - ie what range of input voltage from the batteries will it operate at before it cuts out - 11v-15v, 10.5v-15v, 11.5v-14.5v? This will potentially have a major impact on how long the batteries will last before the invertor cuts out.
third check if it's a square wave, modified sine wave or pure sine wave invertor. Basically the square wave ones are generally the cheapest, and pure sine wave the most expensive. If it doesn't say then I'd presume it'd be a square wave one, coz the pure sine wave ones tend to make it obvious. Basically this matters if you're using it for sound as square wave invertors will generally send a big buzzing sound through the system, and depending on how sensitive your amp is may fuck it completely.
the diagrams below should show you why, basically the invertor is doing 2 jobs, changing the voltage upto 240 volts, and changing from direct current to alternating current. Square wave invertors make a very basic attempt at aproximating AC, modified sine wave are a bit better, and pure sine wave are 99% perfect.
square wave
modified sine wave & pure sine wave
If you've already bought your invertor though it's worth checking it out with you amp as different amps react differently to it, and some basic invertors are better than others.
**
ok as wouldbe suggests the invertor will not be 100% efficient, if it's a cheap one then it could well be only 85% effecient (feel the heat they give off and you'll understand why). This means that if it was capable of doing 500 watts continuous this'd be giving you 500/230 =2.2 amps from the invertor (most invertors actually kick out at 230 rather than 240 volts)... but actually drawing (2.2/85)*100 = 2.58 amps from the batteries.
If you were running this full tilt at 500 watts continuous you'd be drawing 2.58 amps per hour / 2.58 ah.
How long you can run it then depends on how long the batteries will run before the voltage drops under the operating voltage range of the invertor, which depends on the type of battery, rate of discharge, and operating voltage range of the invertor.
free spirit
more tea vicar?
i might just plug stuff in and see what happens.
you all forgot the bit where i was stupid
you all forgot the bit where i was stupid
i dunno - the lights are fitted to the vehicle, they're small and in truth would probably run off a 12volt if they hadn't been converted (suspect that was their original use) and the radio is a little Pure DAB portable with a DC adaptor, so not much. The stereo - if i take it - is one of those T-Amps with, again, a DC adaptor.
nothing here is going to be a big guzzler of energy, i suspect
nothing here is going to be a big guzzler of energy, i suspect
we're using the following set-up
leisure battery > inverter (as yet unseen, it's being borrowed, but i know it's 500w) > two pin connection to those big sockets used for outdoor mains feeds > household sockets fitted throughout the van, plus fitted lights.
how would i attach a charger directly to a battery? and could I then run other stuff?
leisure battery > inverter (as yet unseen, it's being borrowed, but i know it's 500w) > two pin connection to those big sockets used for outdoor mains feeds > household sockets fitted throughout the van, plus fitted lights.
how would i attach a charger directly to a battery? and could I then run other stuff?
free spirit
more tea vicar?
oh bum - it'd seem you're right. been a while since I did stuff with inverters.WouldBe said:
scratch what I said above then
Backatcha Bandit
is not taking your calls
A couple more tips to add to the confusion:
Between the battery and inverter, use the thickest, shortest cable possible. Over any cable there will be a voltage drop, but this is less the thicker the cable and more the higher the current, (but the same irrespective of voltage).
We measure this voltage drop in terms of 'volts per amp per metre'.
Here's an example:
Say you're running a 500W load - as Wouldbe says that's over 40 Amps at 12 volts.
If you tried to get that down a long, thin cable, you could be losing a volt on the way.
At 12 volts, that's a fair percentage - and if your inverter is set to shut down at 10.5 volts, it will be shutting down when the battery hits 11.5 volts. Not good.
Using the same cable to power a 500w appliance at 240v, you're drawing much less current (just over 2 Amps) for a start (so less voltage drop) plus whatever voltage drop you did experience would be a much smaller proportion of the 240v (a 240th, rather than a 12th).
That's why 'mains' wiring is thin compared to 'low voltage' wiring.
For a 500w inverter, the absolute minimum (if you're planning on running a full load) thickness for the input wire is 6mm square (cross-sectional surface area), but personally I'd go for at least 16mm csa.
The other consideration, of course, is that if you use too thin a wire, you run the risk of it overheating and causing a fire.
It's also a good idea to earth the inverter to the metal body of the van - most inverters have a little screw tag just for this.
Between the battery and inverter, use the thickest, shortest cable possible. Over any cable there will be a voltage drop, but this is less the thicker the cable and more the higher the current, (but the same irrespective of voltage).
We measure this voltage drop in terms of 'volts per amp per metre'.
Here's an example:
Say you're running a 500W load - as Wouldbe says that's over 40 Amps at 12 volts.
If you tried to get that down a long, thin cable, you could be losing a volt on the way.
At 12 volts, that's a fair percentage - and if your inverter is set to shut down at 10.5 volts, it will be shutting down when the battery hits 11.5 volts. Not good.
Using the same cable to power a 500w appliance at 240v, you're drawing much less current (just over 2 Amps) for a start (so less voltage drop) plus whatever voltage drop you did experience would be a much smaller proportion of the 240v (a 240th, rather than a 12th).
That's why 'mains' wiring is thin compared to 'low voltage' wiring.
For a 500w inverter, the absolute minimum (if you're planning on running a full load) thickness for the input wire is 6mm square (cross-sectional surface area), but personally I'd go for at least 16mm csa.
The other consideration, of course, is that if you use too thin a wire, you run the risk of it overheating and causing a fire.
It's also a good idea to earth the inverter to the metal body of the van - most inverters have a little screw tag just for this.
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