Power inverter question

**menudude** · 08-28-2009, 09:55 AM

Thank you... I honestly tried searching but I must not of used the right keywords

**IssaquahWA1979** · 10-13-2009, 05:13 PM

the wattage of the inverter does not play any impact on the lack of amp hours the battery can provide and although I agree the DC supplies are more efficient you are not talking about changing the run time by hours more like minutes. Regular vehicle starting batteries are designed to crank an engine for a short period at very high discharge rates they do not like being slowly discharged down to dead as this over time kills them and its why they do not do the job well.

**menudude** · 10-13-2009, 06:21 PM

Originally Posted by IssaquahWA1979

the wattage of the inverter does not play any impact on the lack of amp hours the battery can provide and although I agree the DC supplies are more efficient you are not talking about changing the run time by hours more like minutes. Regular vehicle starting batteries are designed to crank an engine for a short period at very high discharge rates they do not like being slowly discharged down to dead as this over time kills them and its why they do not do the job well.

Thanks for your help, you think i should replace the battery?

**IssaquahWA1979** · 10-13-2009, 07:13 PM

if you are planning to use the system with the vehicle off for durations of time then yes I would or put a secondary battery on a battery isolator and use a deep cycle battery for the pc. I know many like the optima line but I have found them to be disappointing when it comes to long term durability and output performance I myself prefer odyssey batteries although expensive will last a long time and give some exceptional performance, Sears has a house brand that is actually Odyssey.

Based on your 180 watts of usage you can roughly figure 18 amps of current draw (adding in some room for inverter and cable losses) so if you add that up per hour and multiply by 2 that is what size battery you should be using. So for example if you want to run your system for say 10 hours you would need a 180 amp hr. battery at full discharge. So in reality you need two of them in order to only pull the battery down 50% which is about as low as you want to go for repeated discharge cycles. If it sounds expensive it is, not to mention not very practical when it comes to the weight of such sized batteries.

One other thing I might add is you may want to use a watt meter to see how much power you are really pulling with the PC or a ammeter to see exactly what you are pulling from the battery, this will give you some real numbers to base your run times and battery needs in order to fill your run time expectations.

**menudude** · 10-13-2009, 07:16 PM

Originally Posted by IssaquahWA1979

if you are planning to use the system with the vehicle off for durations of time then yes I would or put a secondary battery on a battery isolator and use a deep cycle battery for the pc. I know many like the optima line but I have found them to be disappointing when it comes to long term durability and output performance I myself prefer odyssey batteries although expensive will last a long time and give some exceptional performance, Sears has a house brand that is actually Odyssey.

Based on your 180 watts of usage you can roughly figure 18 amps of current draw (adding in some room for inverter and cable losses) so if you add that up per hour and multiply by 2 that is what size battery you should be using. So for example if you want to run your system for say 10 hours you would need a 180 amp hr. battery at full discharge. So in reality you need two of them in order to only pull the battery down 50% which is about as low as you want to go for repeated discharge cycles. If it sounds expensive it is, not to mention not very practical when it comes to the weight of such sized batteries.

One other thing I might add is you may want to use a watt meter to see how much power you are really pulling with the PC or a ammeter to see exactly what you are pulling from the battery, this will give you some real numbers to base your run times and battery needs in order to fill your run time expectations.

Thanks for your help. It looks like the cheapest route would be a laptop or small carputer. I appreciate the time you took to answer my questions.

**IssaquahWA1979** · 10-13-2009, 07:18 PM

not a problem at all for those of us with big trucks and lots of batteries I can be kind of arrogant about not worrying about the power consumption but with smaller cars its really a big thing as the battery capacity is much less and the room for such things is much harder to accomplish. you may want to consider some of the smaller carputers others have mentioned as they consume far less power.