# Battery Charger run off AC inverter-BAD Idea??



## Paperdesk (Aug 28, 2007)

Here's the issue,

Many dc/ac inverters (to convert 12vdc to 110vac) state that you should not use them to charge batteries. I'm wondering if this is some sort of legal disclaimer, or if there is a real issue here?

I only have a 110v charger (Titanium-2800), and am wondering what the issues are with using a small inverter with that charger in a car.

It's not that it's such a big problem for me to get a small travel charger that runs off 12v, but I'm really wondering about this issue anyway.

I'm hoping someone here with more brains than me can figure this out 

Thanks,

Ted


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## D-Dog (Aug 28, 2007)

Hmmm, good question. I have a 300 watt, 400watt, and 600watt inverter and the only battery chargers they say are bad are the ones that have no wall wart/block , like a razor, or ones with hazerdous voltages present at the terminals like for some powertools. I have charged AA nimh and lithium rcr2's with these inverters without a problem, however, you might want to hear another answer or two before you do this, as I could be missing something. The inverter you have probably outputs a modified-sine wave or a step(p?)ed-sine wave. This should not pose a problem, as most ac products drop the sine wave of ac into a square wave (straight up and down) anyways before recharging a spotlight or running a computer, etc. The only thing is you might hear a slight humming or the product might get a little warmer. Then again, better to error on the side of caution, so I would wait for Silverfox or one of the others too


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## Paperdesk (Aug 28, 2007)

So it may depend on the sine waves? I could try to find out what my inverters produce . . . The smallest inverter I have is only 70 watts, and the largest 1000. I've used them both in the past and they did seem to work, but I don't know if I'm damaging the chargers, cells or maybe the inverter? Thanks D-Dog for weighing in.


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## WildChild (Aug 28, 2007)

Paperdesk said:


> So it may depend on the sine waves? I could try to find out what my inverters produce . . . The smallest inverter I have is only 70 watts, and the largest 1000. I've used them both in the past and they did seem to work, but I don't know if I'm damaging the chargers, cells or maybe the inverter? Thanks D-Dog for weighing in.



Most inverters produce modified sine waves (square wave). I have the same warning on the inverter I just bought, but they say for charging NiCD cells... That's strange. I tried a cell phone charger with no visible ill effect with it. The funny part is that I bought this inverter to charge NiMH and Li-Ion batteries and to use my laptop.


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## Paperdesk (Aug 28, 2007)

I also only purchased the inverter for laptop use (which also involves battery charging) and charging AA cells.

So what bad things can happen if you charge batteries this way? Why would they warn us not to use it if it's not really a problem?


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## D-Dog (Aug 28, 2007)

The only time it is a problem is if the device plugs right into a wall (no transformer) or if the charging circuitry is in the battery, like some power tool packs.


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## JimmyM (Aug 28, 2007)

A true sine wave inverter is no problem whatsoever. There are 2 kinds of modified sinewave inverters and then there are the worst ones... squarewave. The problem with non-sine wave inverters is that electronic power supplies (not just a simple transaformer), is that some use "zero-crossing" switching. The inernal switching can become "confused" when the voltage switches too quickly from (-) to (+). A sine wave is gradual. The modified sine inverter flavors differ in the voltage step from zero to peak voltage. (The voltages I use are examples) The simpler versions go from +100V to 0V almost instantly, then holds for 1/240th sec, then switches to -100V almost instantly, then holds for 1/240th sec, then switches to 0V almost instantly, and holds again for 1/240th sec.
The "better" ones have an additional step between +100V and 0V.
So it goes from +100 to +50 to 0 to -50 to -100.
When you rapidly switch from 0V to 100V or 0V to 100V there is a current spike. The bigger the voltage step, the bigger the spike. That's why things run warmer on mofified sine inverters than on true-sine. Even more heat on a square wave.


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## Paperdesk (Aug 28, 2007)

Wow JimmyM. Great explanation! I guess there is no real way to know what kind of power my inverters use, short of contacting the manufacturer? I would assume, that if they say it's not recommended, then probably they use the "bad" sine wave patterns?


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## JimmyM (Aug 29, 2007)

Paperdesk said:


> Wow JimmyM. Great explanation! I guess there is no real way to know what kind of power my inverters use, short of contacting the manufacturer? I would assume, that if they say it's not recommended, then probably they use the "bad" sine wave patterns?


If your inverter in pretty new and does NOT have a giant transformer in it, it's most likely a modified sine wave inverter. If you look at inverters in the same power range as yours and see most are more expensive, you most likely have the "1 step" modified sine type. If you see that yours is on the pricier end of things, you probably have the "2 step".
What manufacturer and model number? Titanium-2800 (just re-read your OP.)


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## turbodog (Aug 29, 2007)

Yeah, what he said. Some things depend on sort of "watching" the waveform itself. They will miss the switchover and "latch" sort of wide open. Not a good thing.

I don't know of ANY pure sine wave units for sale at typical local places. If they ARE pure sine, they WILL say it.

Also, FWIW, computer UPS supplies SOMETIMES (read the model specs) have pure sine output. I know the apc smart-ups series is pure sine output.


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## Paperdesk (Aug 29, 2007)

I got the small inverter at Costco. It was pretty cheap, like between $10 and $20. It's a Vector Pocket Power Inverter VEC047CD.

Here's a link I found that shows the same inverter: http://www.buymebuyme.com/retail/customer/product.php?productid=45480&cat=283&partner=froogle

My charger is the Tg-2800 from Amondotech. My charger plugs streight into the wall.

So the question is, assuming this is one of the "bad" ones, what will that do to my charger? Could the voltage spikes could fry it, even though it's being converted down to dc again?


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## JimmyM (Aug 29, 2007)

Paperdesk said:


> Ditto the "latch" comment.
> My charger is the Tg-2800 from Amondotech. My charger plugs streight into the wall.


Is it kind of heavy, like it's got a transformer in it? If so, it's probably a safer bet than just the tiny switched mode supplies used by cell phones, etc.
On a side note: I've got a Porta-Wattz 1000 (modified sine, 1200W peak, 1000W 5min, 800W continuous) inverter in my camper. I've run several cell phone chargers and 2 different laptops on it. You do notice that the laptop supplies run quite a bit warmer than normal.
What it won't run... those chasing Christmas lights, 2 different LCD projectors.


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## Illum (Aug 29, 2007)

Paperdesk said:


> So it may depend on the sine waves? I could try to find out what my inverters produce . . . The smallest inverter I have is only 70 watts, and the largest 1000. I've used them both in the past and they did seem to work, but I don't know if I'm damaging the chargers, cells or maybe the inverter? Thanks D-Dog for weighing in.


 
most budget inverters are modified sine...which doesnt really effect equipment to my experience but causes additional heat output in a few power adaptors and causes a humming noise from any wire wound coil motors or permanent magnet motors. 

Modified sine at 600watt runs around ~$100
true sine at 600 watt runs around ~$250 and very very hard to find in stores, but its the cleanest power source you can use
if you want to invest in one I'd recommend buying from solardyne

I use a 400 watt from vector manufacturing for years running everything from fans to laptops to area lights [hurricane evac, no power] with no issues...another thing I noticed...my laptop [Toshiba A15-S129, old old chunk of technology]seem to charge slower than wall power by about half an hour to a full hour and the adaptor gets HOT, but charging my new laptop [IBM X32] has no issues.


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## Paperdesk (Aug 29, 2007)

Really great info everyone! My inverter does feel heavy for it's size, but it is still very small and was cheap, so I'm assuming it's modified sine.

I also noticed my laptop adaptor does get really hot. Probably not a good thing for my rechargable batteries! Based on this info, it sounds like my AA battery charger isn't likely to be damaged by plugging it into this inverter, but perhaps the additional head could damage the batteries themselves (since my unit is the plug in the wall kind, no cord or wall wart).

Anyone else come to the same conclusion?


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## JimmyM (Aug 29, 2007)

Paperdesk said:


> so I'm assuming it's modified sine.


Probably a safe assumption. Use the batteries until they're dead then plug it into the inverter and let 'er rip. See what happens. Most likely, nothing scary.
I love inverters. I have 2 Deka 9C12 batteries (130lbs ea) totaling ~450AH in my popup for "dry camping". I can run all week using the inverter for fans, laptops, cell phones. It's great.

Enjoy.


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## D-Dog (Aug 29, 2007)

I too say it's a modified-sine wave one, since almost all pure-sine wave ones will advertise it right on the inverter. In addition, I have charged ni-mh, lithium, and I could ni-cd using my modified-sine wave with no problem. These chargers plug directly into the wall and I haven't had any heat problems

My laptop has run for hours off my inverters and has experienced no ill effects except for more heat in the block


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## lowatts (Aug 29, 2007)

I just bought a Sam's Club house brand 500 Watt inverter. I think the normal price is over $50 but was being cleared out at under $19. It comes with cords for direct battery connectiona and lighter socket connection.

Its instructions says it puts out modified sine wave, even includes a picture of its output compared to pure sine wave, pretty unusual to have this much technical information for a low end consumer product. It also says not to use it with devices that charge themselves, but OK to use with chargers. That's what puzzles me, why OK to use on chargers but not OK for devices that have internal chargers???


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## Paperdesk (Aug 29, 2007)

Good question Iowatts! That is a unique distinction.

I'll run a test charge cycle with my charger and inverter, and post what happens. I'll specifically pay attention to how hot everything seems to get.


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## jrmcferren (Aug 29, 2007)

Your safest bet would be to use a charger that has a switchmode power supply. Switchmode power supplies usually like modified sine wave versus a sine wave. My charger has a 12 volt input, put I don't know the regulation requirements (comes with a switchmode power supply) so if I need to go mobile with it I will use my 200 watt inverter.

Iowatts:
Do not exceed about 150 watts with the cigar lighter cord (unless the lighter has a 20 amp fuse then the limit is around 200 watts). The cigar lighter cord was provided for convenience (and may even have a lower-rated fuse for the purpose) and the direct connect is for higher power.


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## johnny13oi (Aug 30, 2007)

How can one tell if their device has switch mode power supply?


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## jrmcferren (Aug 30, 2007)

The easiest test for a switchmode power supply is to see if the voltage range is from 100 volts to 240 volts. This test has never found a false positive for me in any device made after the 1980s, but this test will have many false negatives.


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## Illum (Aug 30, 2007)

lowatts said:


> Its instructions says it puts out modified sine wave, even includes a picture of its output compared to pure sine wave, pretty unusual to have this much technical information for a low end consumer product.



not really...I'd be surprised if my inverter DIDN'T have the information
mine was in the back of the instruction manual 
I'm surprised Vector manufacturing included anatomy shots of their inverters 
http://www.andyhweaver.com/inverter/vector_lg.jpg

Looked about right when I disassembled it trying to figure out why the "turbo fan" never turned on once during its service of 3 years while a lesser 300 watt from another company had the fan running the moment it was switched on.

hey, does anyone have issues with using the radio while running the inverter? 
I get a wall of static on just about every frequency..which goes away immediately after I shut off the inverter


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## TPA (Sep 11, 2007)

Yep. Typically inverters are very noisy RF-wise. The higher quality pure sinewave units are much better in this respect. Also, a good radio goes a long way with this as well. I've had the best luck with Sony car radios in terms of working in high RF environments. I actually have a Sony car radio mounted in the audio rack directly next to my computer, perfect AM radio reception with no hetrodynes/whines/noises in the signal, even at night.


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## Illum (Sep 13, 2007)

Battery Charger run off AC inverter-BAD Idea??
only if your running the charger for the battery off the AC inverter installed on the battery...its almost like plugging an UPS onto itself

TPA, I understand.....but the interference only occurs when I'm running something like a 60 watt bulb...but not when I'm running a 40w fan or anything that has a motor in


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## TPA (Sep 14, 2007)

Illum_the_nation said:


> Battery Charger run off AC inverter-BAD Idea??
> only if your running the charger for the battery off the AC inverter installed on the battery...its almost like plugging an UPS onto itself
> 
> TPA, I understand.....but the interference only occurs when I'm running something like a 60 watt bulb...but not when I'm running a 40w fan or anything that has a motor in



No, there are some serious issues with cheaply built chargers and modified sine wave power. I've seen more than a few powertools' batteries (and sometimes chargers) get toasted by the mod sine wave. Apparently these chargers just use a rectifier or two to convert AC to DC with minimal . Works fine under "normal" conditions, but with modified sine wave, your peak voltages will be different as well as the timing of the rise/fall of the cycle. Even decently-built power supplies will run warmer on modified sine wave because of the different waveform. 

As far as the RF noise, here's my guess as to what's happening:

With AC power, there's something called power factor. Basically not everything is 100% "efficient" at pulling power from the powerlines and will send some of it "back" through the neutral (very poor, oversimplified explanation, google power factor for more info). Incandescent lights have a power factor of 1.00, which means they are using everything they can get from the powerlines. Electric motors vary, but often have a power factor of ~0.35-0.65. I'd imagine some of the "power being fed back" helps cancel out some of the RF noise while the circuit with only the light bulb ends up being an antenna.


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## JimmyM (Sep 14, 2007)

The RF noise comes from the "hard" switching used in modified sine wave inverters. The internal switching causes "ringing". A high frequency distortion in the wave form just after the internal switch (probably mosfets) turn on or off. It would look like a jagged line on an oscilloscope immediately after a voltage transition. These distortions generate frequencies in the radio band.
Power factor is a measure of the Volts*Amps versus Watts. In a DC circuit Watts=V*A. In an AC Circuit, Watts=V*A*PowerFactor. In an AC circuit a power factor is the relationship between the voltage and current waveforms. In an purely resistive circuit the voltage and current wave forms are completely in phase and have a power factor of 1.00. In an inductive circuit, current lags voltage. The greater the phase offset, the lower the power factor (In inductive circuits, it's often referred to as a Lagging Power Factor). Inductive loads are frequently coupled with capacitors to raise the power factor. Current Leads voltage in a capcitive circuit.


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## TorchBoy (Sep 14, 2007)

Purely anecdotal, I realise, but I've used a couple of NiMH battery chargers (both apparently with switchmode power supplied) and CFLs from my Xantrex inverter without problem.


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## JimmyM (Sep 14, 2007)

TorchBoy said:


> Purely anecdotal, I realise, but I've used a couple of NiMH battery chargers (both apprently with switchmode power supplied) and CFLs from my Xantrex inverter without problem.


 
Which Xantrex model? I've got some of their equipment in my camper (TrueCharge40, Link10, Portawattz 1000). I've got a pair of Deka 9C12 batteries. That last bit was way off topic, but I wanted to brag.


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## TorchBoy (Sep 15, 2007)

Are those really Xantrex models? It doesn't look like it.

See this post for my rave about my inverter. I've also carried it around in a backpack (while using it) - heavy, but o so good.


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## JimmyM (Sep 15, 2007)

TorchBoy said:


> Are those really Xantrex models? It doesn't look like it.
> 
> See this post for my rave about my inverter. I've also carried it around in a backpack (while using it) - heavy, but o so good.


 
They're xantrex models NOW. Xantrex went around and bought up other companies, or a bunch of companies merged. Heart Interface, Trace, StatPower and a few others.


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## TorchBoy (Sep 15, 2007)

JimmyM said:


> They're xantrex models NOW. Xantrex went around and bought up other companies, or a bunch of companies merged. Heart Interface, Trace, StatPower and a few others.


Well well, I do live a sheltered life. Thanks. :twothumbs


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## D-Dog (Sep 16, 2007)

I have used the Xantrex xpower 300, 600, and 1500 before with a number of charger now and hove not had a single problem.


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## txmatt (Sep 17, 2007)

I had an older Canon digital camera (S110) that its battery charger wouldn't peak-detect and stop the charging process of the lithium battery if the charger was plugged into a modified sine wave inverter. That's about the only issue I've had.

I now run a Maha 204 directly from 12VDC for AA/AAA NiMH charging while camping and a pure sine wave inverter for other uses.


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## TorchBoy (Sep 17, 2007)

txmatt said:


> ... its battery charger wouldn't peak-detect and stop the charging process of the lithium battery ...


I don't think lithium batteries have a peak like NiMH does. If I understand it correctly they use voltage controlled charging, not current controlled charging. Maybe the charger was getting confused and supplying a higher voltage than it should have. That wouldn't be good for the battery.


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## txmatt (Sep 17, 2007)

Whatever charge completion algorithm it used, the charge light would never turn to green indicating it had finished charging. I assumed the "noise" associated with the non-sine wave supply power interfered with detection of charge completion. I still used it to charge this way when I needed, but only for a couple hours at a time.


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## TorchBoy (Sep 17, 2007)

I'd say you're right Matt, and stopping it after a couple of hours sounds like a good idea. Did you measure any voltages while it was charging? There's a graph in this article which shows what the voltage of lithium chargers are doing: http://www.caplamp.org/Knowledge/Charging_lithium-ion_batteries.htm


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## txmatt (Sep 17, 2007)

Nah, never really did any testing with it. I only needed to charge with the inverter a few times on camping trips before I upgraded digital cameras so I never took the time to investigate further.


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## TPA (Sep 18, 2007)

Hm.. I'm curious, but not curious enough to try this myself (only had my Maha C9000 & 800S for about 24 hrs now)... How well do the Maha 800 & 9000 series chargers work on mod-sine-wave power?


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## SilverFox (Sep 18, 2007)

Hello TPA,

I don't know about the 800S, but the C-9000 works great on 12 volts.

Tom


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## cy (Sep 18, 2007)

my APC 500,(probably not smart series) measures 80 volts no load, with std voltmeter. same unit with Fluke 87 RMS meter shows 106.8v under load with cord unplugged. 



turbodog said:


> Also, FWIW, computer UPS supplies SOMETIMES (read the model specs) have pure sine output. I know the apc smart-ups series is pure sine output.


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## JimmyM (Sep 19, 2007)

TPA said:


> Hm.. I'm curious, but not curious enough to try this myself (only had my Maha C9000 & 800S for about 24 hrs now)... How well do the Maha 800 & 9000 series chargers work on mod-sine-wave power?


Hey, those babies are under warranty. I smell a torture test! If you let the smoke out, return them for replacements.


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## TorchBoy (Sep 19, 2007)

SilverFox said:


> Hello TPA,
> 
> I don't know about the 800S, but the C-9000 works great on 12 volts.
> 
> Tom


Tom, have you ever measured the current at 12V they use? And how does that relate to charge current?


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## SilverFox (Sep 19, 2007)

Hello Ian,

I believe it draws just over 2 amps.

Tom


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## TorchBoy (Sep 19, 2007)

SilverFox said:


> I believe it draws just over 2 amps.


What about at lower charge rates, do you know?


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## SilverFox (Sep 19, 2007)

Hello Ian,

I don't know, but would speculate that the current draw would follow the charge rates.

Tom


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