Using 3 LiGo batteries to charge a computer.

[zacksc]

I was thinking of using 3 LiGo batteries in series to charge a laptop computer. Making an Anderson to 110 volt (female) adapter and then plugging my MacBook charger into that. Does that sound safe? Will it work okay? Have you guys done that. (Ligo is a 36 volt 98 watt-hour Li-ion battering from Grin Technologies.)

All advice is welcome; advice about safety is especially welcome. I do not have a lot of experience with dc voltages above about 40 volts.

 

[fechter]

Look at the input voltage rating on the charger. If it is a wide input range, like 100-240 vac, then the Ligo pack should work fine. There is a good chance it would work with only 2 Ligos in series (72v).

 

[zacksc]

polarity?
So on the 110 plug there is the side where the wider blade plugs in, which has a silver screw; and then the side connected to the thicker blade slot, which has a gold colored screw. Which one should be positive and which one negative, for the 120 volt DC input??

 

[zacksc]

Look at the input voltage rating on the charger. If it is a wide input range, like 100-240 vac, then the Ligo pack should work fine. There is a good chance it would work with only 2 Ligos in series (72v).

Thanks. I think the charger uses what is called a switch mode power supply. I'll try it with 3 Ligos first and then drop try dropping down to 2 Ligos next. Is the polarity important?

 

[zacksc]

I mean I imagine it probably doesn't matter, but is there any reason to prefer connecting the plus side of the battery to the wide blade side of the 110 v plug or visa versa?

 

[fechter]

With most of them the polarity won't matter. It goes through a bridge rectifier first. If it doesn't turn on, you could try reversing the polarity. I don't think you can hurt anything if it doesn't work.

One other thing I should mention; you can expect a pretty impressive spark when you connect or disconnect the charger. If you plug and unplug quickly, it won't spend much time arc welding the plug and damage will be minimal. After hundreds of plugging cycles the prongs may get sort of fried.

 

[zacksc]

With most of them the polarity won't matter. It goes through a bridge rectifier first. If it doesn't turn on, you could try reversing the polarity. I don't think you can hurt anything if it doesn't work.

One other thing I should mention; you can expect a pretty impressive spark when you connect or disconnect the charger. If you plug and unplug quickly, it won't spend much time arc welding the plug and damage will be minimal. After hundreds of plugging cycles the prongs may get sort of fried.

I was thinking I would do the plugging and unplugging at the Anderson connectors. Does that seem safe?

 

[zacksc]

How come there is a big spark? Is there a high transient current? (Or maybe I don't understand what makes sparks)

The charger is about 40 watt so the steady state current would be about 1/2 amp.

 

[Upnorth]

I may be missing something here.....

You are powering a laptop charger with a Li-ion pack correct? With no inverter in the circuit?

There is a Massive difference between AC and DC current..... particularly with safety. 100volts DC from three sizeable packs can do some serious damage.

I suspect the charger can not accept DC input.

However the charger will likely output 12volts DC to the laptop. The laptop itself will have a charge controller that will use the 12volt DC supply to charge it’s batteries, likely a string of 18650 cells.

So it is likely possible to skip the charger all together and supply 12volts DC directly to the laptop..... Be careful though! The internal charger in the laptop may have very narrow voltage supply limits.

My question is:
Does the supply to the laptop require a current limiter or will the internal charger take care of that??

In regards to “polarity” on AC plugs: It will work either way ( the current alternates). However it is much safer to keep the “hot” on the supply going to the correct lead, this makes the power device safer depending on its construction, prevents the possibility of the case of the device becoming “hot”. This is why modern plugs and cords have one blade wider but older ones that don’t still work either way.....


DC and AC are not interchangeable without a converter or inverter.

 

[fechter]

How come there is a big spark? Is there a high transient current? (Or maybe I don't understand what makes sparks)

The charger is about 40 watt so the steady state current would be about 1/2 amp.

There is a big capacitor downstream of the bridge rectifier that will charge suddenly when you make the connection. You would get the same spark plugging into an AC outlet if it happened right when the AC voltage was at it's peak. Since the charger isn't very high power, the spark won't be too big, just something to be aware of.

The typical laptop charger "brick" is a switching mode power supply. The AC line is rectified to DC in the first stage, so feeding it DC works fine. I've done it with all kinds of switching power supplies. Many of them will work fine at reduced voltage. Rectified 120VAC will be around 170VDC when there is a capacitor downstream of the rectifier.

 

[Upnorth]

My mind is blown......
Never would have thought that plugging dc into a ac to dc converter would work.

Could I plug a 58vlt dc battery into a laptop charger and have it work??

 

[amberwolf]

Quite possibly. But there are catches.

An SMPS is, at base, a DC-DC converter.

If it is part of a wall-plugged AC power supply, then it just has a rectifier to turn the AC to DC, and some very large capacitors to smooth out the AC ripple in the DC, before it goes into the SMPS part.

If you use DC on it, then it just essentially bypasses the AC stuff and goes right to the SMPS (effectively, not literally).

The DC just has to be high enough votlage to be equivalent to the rectified AC voltage.

Many AC SMPS PSUs will oeprate from around 100VAC to around 250VAC, it'll be printed on the lable what the actual range is, but if it's 100VAC, it's around 72VDC, IIRC.

Many will actually power on at a much lower voltage, but htey are unable to supply tehir full output current this way. It's possible to damage one if runnign too low a voltage on it's input while putting enough of a load on it to draw full current. I did this to one, by running the laptop while the PSU was on a 14s battery instead of AC, when it had worked perfectly just charging the laptop battery from it previously.




A few are designed in a way that doesnt' allow pure DC to power them, like the XBox360 PSU. That one has some portion of teh circuit that will not kick on without an AC input waveform. :/

 

[fechter]

My mind is blown......
Never would have thought that plugging dc into a ac to dc converter would work.

Could I plug a 58vlt dc battery into a laptop charger and have it work??

That might be sort of borderline. Some work better at lower voltages than others. If the input voltage gets too low, the output will start to drop below spec. Easy enough to try. Good if you can measure the output when testing.

 

[zacksc]

Thanks a lot F and A. Good education I am getting here! Much appreciated

 

[zacksc]

I am thinking that with 3 batteries in series, that if I keep them above 30% then balance doesn't really matter. And that can mix Ligo (MJ?) and Ligo+ (30Q) and in even pairs in parallel with singles. Sound okay?

 

[fechter]

If using packs in parallel you need to have them within about 0.1v before connecting together, otherwise as long as you don't get close to zero SOC, the balance isn't a big issue. This assumes they are charged separately.

 

[zacksc]

Thanks fechter. I have a pair of Ligo+ that I keep in parallel all the time and use as a 10x2, so I was hoping not to break those up. Then I also have two individual Ligos to put in series with that pair. I charge each of them at 36 volts (2 amps), with a charger from Grin. So one unit in the series chain (the Ligo+ pair) will be a lot stronger than the other two, but I am thinking you are saying that doesn't matter as long as I don't drive the weaker ones below 30%.

 

[zacksc]

It is working good! Thanks a lot!

I wonder if I can power a charger for a portable vacuum cleaner with DC like this? Dust buster type ?

 

[amberwolf]

If it says it's 100-220vac (or thereabouts) wide voltage input range, at 50-60hz (rather than a specific frequency and single voltage), it is likely it will work.

The DC-DC / SMPS types generally are lightweight, whereas the transformer types that will not work on DC are heavier, typically bulkier, for the same output voltage/current levels.

If you can put a multimeter set to 20Ohms range across the AC prongs of the device (when not plugged into anything) and get a low ohms reading, it is a transformer type and can't be used with DC input.

 

[zacksc]

It is a 16 volt black and decker. Maybe that is a switch mode PS as well. What is the potential downside in that ?

 

[zacksc]

Thanks AW. It is about 5 or 6 Meg Ohm. also light weight

 

[zacksc]

what would happen if I tried koto power a transformer type ps with DC?

 

[zacksc]

I mean I see why it would not work, I guess because it is inductive... but would anything bad happen?

 

[amberwolf]

Replies to each above post are together here:

Downside in what? If you mean, "downside in being a switchmode PS", there isn't one in regards to your intent, because it being one is the only way you can do what you want. If it isn't one, you can't.

I suspect by "16v" you mean the device itself, but that's irrelevant, because you're trying to power it's charger. If that's the case, you need to look *at the charger*, not the device, for the *wall-plugin-side voltage/etc information*, not the output side that plugs into the device.


If it's in the megohm range on the AC input, it's not a transformer type, so it at least *might* work with DC input. (never a guarantee. )

If you put DC on a transformer, you are basicaly shorting out the DC source, because a transformer is just a piece of wire to a DC source (they only work with AC). IF the DC source doesn't have a protection to shut it off when shorted, and is capable of sufficient current, and the resistance of the transformer is low enough, it will overheat and potentially set fire to the transformer and wall charger. Additionally, if the DC source is sensitive to overcurrent, or itself has wires thin enough to heat up under these currents, it may itself be damaged.

The actual results will vary depending on the transformer's DC resistance, and the ability of the DC source to supply current to it.

 

[zacksc]

I see. Thanks a lot Amber wolf. So I gather that it is therefore really important to be sure that your power supply is switch mode before you plug it into DC.

I am thinking that the bottom line is: plugging a 110 V switch mode power supply Into a DC source, such as 336 V batteries in series, is fine, But before you do it you should be really sure that the power supply is switch mode and not a transformer.