Author Topic: 12V Power Inverter Question (Read 5709 times)

LeftoverSammy · « **on:** January 23, 2004, 12:53:11 PM »

Hey Now,
I just purchased a 12V, 400W/800W peak power inverter to charge my SLA's at Festy shows during the summer months while camping

. My question is for those who have run these P-inverters via their car or deep cycle battery......how long can you run the inverter to charge your SLA without having to start the car to charge your battery?

In the instructions it says to start your car or RV every 60~90min. to avoid draining your battery and run the car to charge the battery for 10min. However I think this is a general rule of thumb only if you are pulling some serious power (over 150W??).

For example: my older style Eco-charger SC-61 pulls about 20W, 120V @ .18A (180mA). The specs on the inverter say it has an “idle current draw” of .4A (400mA) - meaning it draws this current without any devices attached.

Is it correct to assume that when I hook my SC-61 to this inverter it will draw the .18A (20W) plus the load rated at idle current of .4A for a total of .580A or 580mA? That would be a total power of 70W or so (120Vx .580A = 70W). Is this right?? If indeed this is about what the inverter will pull in terms of power how long will the inverter run @ 70W off a standard automotive battery?

If you consider a standard 12V 12AHr SLA and applied around a 580mA current draw the SLA would only last about 21hrs or so run time wise (roughly). Most of the time my 7.2AHr SLA’s only take about 5hrs or so to charge so wouldn’t an automotive battery which has a much bigger amp hr rating pretty much last all night long??

Does anyone know roughly how much a standard automotive battery is in terms of amp hr ratings?? I don’t want to have to wake up every 2hrs during the night to run my rig for 10min. at a time to recharge my auto battery if its just not needed.

Thanks for any info folks!

LoS

leegeddy · « **Reply #1 on:** January 23, 2004, 01:16:21 PM »

Quote from: LeftoverSammy on January 23, 2004, 12:53:11 PM

Hey Now,
I just purchased a 12V, 400W/800W peak power inverter to charge my SLA's at Festy shows during the summer months while camping . My question is for those who have run these P-inverters via their car or deep cycle battery......how long can you run the inverter to charge your SLA without having to start the car to charge your battery?

In the instructions it says to start your car or RV every 60~90min. to avoid draining your battery and run the car to charge the battery for 10min. However I think this is a general rule of thumb only if you are pulling some serious power (over 150W??).

For example: my older style Eco-charger SC-61 pulls about 20W, 120V @ .18A (180mA). The specs on the inverter say it has an “idle current draw” of .4A (400mA) - meaning it draws this current without any devices attached.

Is it correct to assume that when I hook my SC-61 to this inverter it will draw the .18A (20W) plus the load rated at idle current of .4A for a total of .580A or 580mA? That would be a total power of 70W or so (120Vx .580A = 70W). Is this right?? If indeed this is about what the inverter will pull in terms of power how long will the inverter run @ 70W off a standard automotive battery?

If you consider a standard 12V 12AHr SLA and applied around a 580mA current draw the SLA would only last about 21hrs or so run time wise (roughly). Most of the time my 7.2AHr SLA’s only take about 5hrs or so to charge so wouldn’t an automotive battery which has a much bigger amp hr rating pretty much last all night long?? Does anyone know roughly how much a standard automotive battery is in terms of amp hr ratings?? I don’t want to have to wake up every 2hrs during the night to run my rig for 10min. at a time to recharge my auto battery if its just not needed.

Thanks for any info folks!

LoS

if i'm reading you correctly, you're going take a 12v DC-AC converter to run your 12v AC-DC charger to charge your 12v SLA?

why don't you just charge your 12v SLA via your RV's battery?
seems like an aweful lot of wasted energy in heat dissipation from your 2 conversion steps.

marc

LeftoverSammy · « **Reply #2 on:** January 23, 2004, 02:02:26 PM »

No, you are missing the point.

I used the 12V SLA as a COMPARISON illustrating current drain on a 12V SLA vs. one an 12V automotive battery. MY SLA's that need to be charged are 6V not 12V. So I DO need a DC/AC converter to run my AC charger in the field.

Now if I had some sort of DC charger that stepped down from 12V to 6V then I would not need a power inverter would I now?? I'm pretty sure ANYONE who is charging 6V SLA's while at festy's are using 12V power inverters to run their AC to DC 6V chargers......

If my math is correct one could expect to run this power inverter that is only drawing a meger 70W for many hours on a standard auto battery....I'm just looking for feedback to those of which who have.

LoS

rustoleum · « **Reply #3 on:** January 23, 2004, 02:06:19 PM »

The invertor I use has a "low" power light that will alert me when I am approaching the point that I won't be able to start my car. I'm going to guess that yours doesn't have that nifty little feature?

Rusty

leegeddy · « **Reply #4 on:** January 23, 2004, 02:57:20 PM »

Quote from: LeftoverSammy on January 23, 2004, 02:02:26 PM

No, you are missing the point. I used the 12V SLA as a COMPARISON illustrating current drain on a 12V SLA vs. one an 12V automotive battery. MY SLA's that need to be charged are 6V not 12V. So I DO need a DC/AC converter to run my AC charger in the field.

Now if I had some sort of DC charger that stepped down from 12V to 6V then I would not need a power inverter would I now?? I'm pretty sure ANYONE who is charging 6V SLA's while at festy's are using 12V power inverters to run their AC to DC 6V chargers......

If my math is correct one could expect to run this power inverter that is only drawing a meger 70W for many hours on a standard auto battery....I'm just looking for feedback to those of which who have.

LoS

i see your objective now.

may i suggest a voltage regulator circuit that will take your 12v and drop it down to what ever voltage you need? you can get a those gadgets in many places.

i think you're making it more difficult than it really is, IMHO. no offense by my statement. it's just that you want to take a DC voltage > convert it to AC voltage > back to DC voltage to charge a DC voltage supply. you're taking a loooong detour to reach your destination.

>>Now if I had some sort of DC charger that stepped down from 12V to 6V then I would not need a power inverter would I now?? I'm pretty sure ANYONE who is charging 6V SLA's while at festy's are using 12V power inverters to run their AC to DC 6V chargers......

perhaps people like to take long detours or show of their nice shiny power inverters.
which route would i rather take?

DC > AC > DC > DC or

DC > DC? the latter is MUCH more efficient, according to laws of physics.

marc

LeftoverSammy · « **Reply #5 on:** January 23, 2004, 03:02:21 PM »

Yes, it has a low battery light indicator and alarm

however it doesn't trigger into alarm until your auto battery reaches 10.5V. I think at that point your car, truck or RV would not start w/out a jump. $:-\$

It would be nice to just plug and forget until its done and not have to worry about starting my rig every now and then.

LoS

LeftoverSammy · « **Reply #6 on:** January 23, 2004, 03:16:27 PM »

Marc,
This is true - a step down circuit is a much more efficient process but not necessarily the best option economic wise. The power inverter I purchased was made by Colman and was only $20 new, so it was pretty darn cheap way to go.

I am not aware of a step down converter on the market (anyone??) that is that cheap unless you build yourself (which could be done with transformers and such but you also risk OVER charging unless it has a smart circuit like my eco-charge does). Last thing I want to do is over charge me SLA in my rig while I sleep and night and inhale acid fumes or risk a fire!!

It really has nothing to do with showing my new toy off or what ever. Perhaps some folks are hung up on that. Penis envy thing I guess. Also, (not taking any offense here) I really don't think it is all that in-efficient going this method. These new generation power inverters are actually very efficient, although perhaps not as much as the path you suggested.

Using my original charger with my SLA's has been recommended by several folks and is a tad bit safer IMO while in a campground where accidents are not really worth the risk. If there was some sort of smart charger on the market that was below or @ $20 then I am all ears bro!!

Thanks for the active conversation!!!

Los

sexymexi · « **Reply #7 on:** January 24, 2004, 12:27:13 PM »

so do you think its possible, well i guess rather i should say safe to charge a 12v sla from your cars alternator?? is that what i'm getting from this? cause you sayd why have the power inverter goign to a charger, then to the sla, but i don't think that it would be very safe to charge a sla from a car's alternator... i'm sure its pushing much more than the battery charger, and could be potentially dangerous to the sla.

personnally i'm looking for a generator for festivals. or just having a lot of batteries on hand. but i've seen generators for pretty cheap, like under $200, or i was goign to rent one for the week, and use it there, and not worry about having dead batts. also a generator would be a really nice thing for your campsite... have the power you need for whatever. good luck.

matt

chase · « **Reply #8 on:** January 24, 2004, 03:36:27 PM »

the best thing to do is befriend one of the vendors and see if you can charge your batteries there. offering to hook them up with copies of the show usually helps. obviously this is not always possible. i wouldn't feel safe using a voltage regulator to run my 12V car battery > 6V SLA. although DC > invertor > AC charger > SLA isn't the most efficient way, it most certainly is the safest. i'd bring some jumper cables just in case. worst case scenario you have to get jumped before you leave.

leegeddy · « **Reply #9 on:** January 24, 2004, 06:10:24 PM »

>>the best thing to do is befriend one of the vendors and see if you can charge your batteries there. offering to hook them up with copies of the show usually helps. obviously this is not always possible.

an excellent idea.

>> i wouldn't feel safe using a voltage regulator to run my 12V car battery > 6V SLA.

why not? there are plethora of manufacturers who make those cigarette-lighter-plug voltage convertors. it's very easy to obtain 6V from one of those gadgets.

>>i'm sure its pushing much more than the battery charger, and could be potentially dangerous to the sla.

my home SLA charger outputs 14V for my 12V SLA. it works just fine. however, i don't think it's safe to hook up your SLA to anyone's alternator and "step on the gas".

my original inquiry was about the extra (and unnecessary) AC step in the original post. he simply wanted to charge his 6V SLA from his car. i merely suggested skipping the AC step all together and just stick with DC.

marc

Author Topic: 12V Power Inverter Question (Read 5709 times)

LeftoverSammy

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leegeddy

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rustoleum

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LeftoverSammy

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sexymexi

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