Battery Charger run off AC inverter-BAD Idea??

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

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

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.

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.

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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.

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?

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.

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.

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?

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?

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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.)

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.

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?

Paperdesk said:

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

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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.

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.

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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.

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?

Paperdesk said:

so I'm assuming it's modified sine.

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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.

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

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???

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.

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.

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