12V DC-AC trace Inverter Question

Illum · Aug 22, 2006

compared to lights this is really off topic... :grin2:

:laughing:

I current have a Vector [VEC024C] 400 watt modified Sine Inverter as an emergency power source in the event of a power outage during a storm. The inverter draws a maximum of 3.8Amps before the safety system shuts the circuitry down.

Inverter: http://www.weatherproducts.com/products_detail.asp?PID=96

Can anyone tell me how to calculate how big of a battery, or batteries [in Amp-hours] I would need to run a 400 watt load for 2 hours.

yuandrew · Aug 22, 2006

I've always used the Don row runtime calculator applet on their site.

http://www.donrowe.com/inverters/inverter_faq.html#how_long

Note: Sorry Netscape and Firefox users; it only works on Internet Explorer

3.8 amps at 120 volts is 456 watts. However, to get the same wattage from a 12 volt source; you'll be pulling about 38 amps from your battery not including the inverter's efficiency. You'll need some 10 gauge wire for that current draw.

Jumpmaster · Aug 22, 2006

Here's another good site...
http://www.sengpielaudio.com/calculator-ohm.htm

JM-99

WNG · Aug 22, 2006

Expect power supply efficiency to be only a little better than 50%.
I'd make sure to wire it with 8GA to the battery for 65A draw.

Bright Scouter · Aug 22, 2006

Well, power in watts - current in amps times voltage. So, guesstimating with not much loss in the inverter, which there will be some,,, I would say your input amperage would have to be about 35 amps to get that much wattage. Could you be pulling the voltage of your battery source down enough to kick in the safety system?

Bright Scouter · Aug 22, 2006

Fine, I guess when I get interupted in the middle of a reply by work, I am late to the answer party! Guess I better stick to work!

Illum · Aug 22, 2006

the specs advertise the safety system to engage when the batter hits 10.5V

yuandrew said:
I've always used the Don row runtime calculator applet on their site.

http://www.donrowe.com/inverters/inverter_faq.html#how_long

Note: Sorry Netscape and Firefox users; it only works on Internet Explorer

3.8 amps at 120 volts is 456 watts. However, to get the same wattage from a 12 volt source; you'll be pulling about 38 amps from your battery not including the inverter's efficiency. You'll need some 10 gauge wire for that current draw.

I'm assuming the calculator meant completely discharging the battery, which technically kills the life of the battery.

38 Amp draw.... :thinking:
the load's one laptop, two florscent lights and half a dozen fans
[Only thing I really need running in a storm w/o power is the phone system, lightning, and ventilation anyway]

Illum · Aug 22, 2006

Another question I forgot to mention when I started the thread, say I've connected the inverter to the battery and begin its operation, if the inverter is rated at 400 watts but im running only a 50 watt load, is it still supplying a full 400 watt power and therefore wasting my battery supply?

Bright Scouter · Aug 22, 2006

No, it will draw current based on the wattage used. But there is a baseline that it will draw at rest also. That has to be added to the drain.

Illum · Aug 22, 2006

Thanks Bright Scouter :wave:

I was just thinking of buying a smaller inverter in case I only needed to run a small load

TedTheLed · Aug 22, 2006

you want 800 watt hours from a battery. (actually 400 watts for 2 hours depletes the battery less than 800 watts for 1 hour) lets says a thousand watts to cover line losses, in and out of the battery losses, etc..

1000 watts/120 volts = lets say 9 (ac) amp hours. at 12 volts that's times 10 so it's 90 amp hours from a 12 volt battery.

when you are done withdrawing that power how full do you want your battery bank to be? if you want only 90 amp hours total, I'd say get at least 180 amp hour battery. bringing the voltyage down to 10.5 will damage the battery, keep it over 11 volts at least while there is a heavy drain on the battery.

I recommend you get something like a pair of Trojan J-250 6 volt batteries, wired for 12 volts. they are about $100 each, and should do the job plus a little extra and still have something left over.. -- if that's too expensive, I wouldn't go much below a 200 amp hour (at 12 volts) battery..unless it's ok that the battery is near dead after 2 hours..

the bigger the battery capacity you buy, the less the drain, the longer the life, the less the cost..

Illum · Aug 22, 2006

TedTheLed said:
you want 800 watt hours from a battery. (actually 400 watts for 2 hours depletes the battery less than 800 watts for 1 hour) lets says a thousand watts to cover line losses, in and out of the battery losses, etc..

1000 watts/120 volts = lets say 9 (ac) amp hours. at 12 volts that's times 10 so it's 90 amp hours from a 12 volt battery.

when you are done withdrawing that power how full do you want your battery bank to be? if you want only 90 amp hours total, I'd say get at least 180 amp hour battery. bringing the voltyage down to 10.5 will damage the battery, keep it over 11 volts at least while there is a heavy drain on the battery.

I recommend you get something like a pair of Trojan J-250 6 volt batteries, wired for 12 volts. they are about $100 each, and should do the job plus a little extra and still have something left over.. -- if that's too expensive, I wouldn't go much below a 200 amp hour (at 12 volts) battery..unless it's ok that the battery is near dead after 2 hours..

the bigger the battery capacity you buy, the less the drain, the longer the life, the less the cost..

For hurricane prepareness applications [where the batteries will be used sparingly and kept at full charge for most of their lifetime, 200 amp hours sounds like a system made for a house:laughing:

but I see where you would get that number :grin2:

this was my original idea... http://www.discoverpower.com/shop/emergency_disaster_camping_power_radio_light_72.asp
60 AH battery to a 1500 watt inverter.

I was trying to build a smaller version of it....from two 18 AH Exide Gel cells [12V each running parallel] and my 400 watter, but I guess 26AH wont last me 2 hours at 400 watt load, thanks...

TedTheLed · Aug 23, 2006

remember watts is always watts (since watts is volts X amps) but amps depends on the voltage. (another way to think of it; you need 10 amps at 12 volts dc to make 1 amp at 120 volts ac)

for my house I have 14 pairs of those J-250 batteries -- housed outside in plastic dog houses..they are over five years old and still going..

btw does everyone have hard wired phones available that run on telephone co. line power, in case the grid goes out? ( I have measured the power from the phone line, and it was around 30 ma -- I forget the voltage -- I'll check later -- but I do know the voltage when it rings is about 90 volts! enough to give you a jolt if you're working with the wires when a call comes in..it's an odd anomally left over from when all phones had heavy mechanical ringers that needed 90 volts to get them ringing! anyway it woud be wrong to use the telephone company power to keep your batteries charged, wouldn't it?)

Brock · Aug 23, 2006

Ya I would suggest at the minimum two T105 type batteries, commonly called "golf cart" batteries. They will vary by manufacture but are typically in the 200 ah range at 6 volts a battery. I have seen so many setups with smaller battery packs and people try to figure out why the system shuts off when kicking on even a small fridge. They smaller batteries can't handle the "punch" from a motor starting. Here is a bit of info on my little system
http://www.uwgb.edu/nevermab/solar.htm

TedTheLed · Aug 23, 2006

many of the larger inverters (like my Trace ps2512) allow you adjust the minimum battery voltage cut-off point..very necessary when running something like your solar jack-hammer..
I guess it would be prudent to set it back up when you're done with your high-drain device, I just hit the reset button which returns the inverter to all default settings..

roknrandy · Aug 23, 2006

Heres something I put together a couple of years ago to use for power outages and emergencies. I get 5 nights (6 hours each) use out of it.

http://members.cox.net/roknrandy1/Machine/Homemade Emergency Power.htm

yuandrew · Aug 25, 2006

btw does everyone have hard wired phones available that run on telephone co. line power, in case the grid goes out? ( I have measured the power from the phone line, and it was around 30 ma -- I forget the voltage -- I'll check later -- but I do know the voltage when it rings is about 90 volts! enough to give you a jolt if you're working with the wires when a call comes in..it's an odd anomally left over from when all phones had heavy mechanical ringers that needed 90 volts to get them ringing! anyway it woud be wrong to use the telephone company power to keep your batteries charged, wouldn't it?

Last time I did some work on my phone line; it's around 45-48 volts DC if I remember and my ring voltage is 95 volts at 20hz frequency. Sure, it could power an LED but putting any load on a phone line is probably going to cause problems. Kind of like leaving a phone off the hook.

I have a back up (later to be solar charged) system myself with a 300 watt True sine wave inverter that runs lights and a TV but I figure if you're going to run anything that has an adaptor (Wall Wart) such as a Laptop or portable radio; it will be more efficient to find a DC-DC converter for your device instead of doing 12 volts DC to 120 volts AC then to 18 volts DC for a laptop or 6 volts DC for my radio. If theres a "good" Radio Shack nearby; they're helpful.

TedTheLed · Aug 25, 2006

so far the highest power wall wart I've found (I think it was at radioshack)
has been an 'emerson universal battery eliminator' with regulated 300ma - 500 - and 1200 ma at 6, 9 , and 12 volts respectively; not enough to power an XM radio receiver ( 5 volts) ..going to a larger dc transformer may or may not be more efficient than going dc-ac-dc -- let me know if you figure something out.

Illum · Aug 25, 2006

yuandrew said:
I have a back up (later to be solar charged) system myself with a 300 watt True sine wave inverter that runs lights and a TV but I figure if you're going to run anything that has an adaptor (Wall Wart) such as a Laptop or portable radio; it will be more efficient to find a DC-DC converter for your device instead of doing 12 volts DC to 120 volts AC then to 18 volts DC for a laptop or 6 volts DC for my radio. If theres a "good" Radio Shack nearby; they're helpful.

True sine eh? thats way more expensive than the modified sine....

at the same rated wattage, does the true sine draw more amperage [under no load/load] than the modified sine?

12V DC-AC trace Inverter Question

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