GH2 GH2 Power - specs, tests, DIY
- Thread starter keylight
- Start date
g.l
Well-known member
I bet it's something really simple that just produces a certain voltage signature.
<snip>
Yes, absolutely. The body can clearly accept a fairly wide voltage range (whatever the bundled batteries' empty cutoff point is -> at least 9V). That's not something I've seen before on a device (not because it can't be done but because it costs a bit more to implement) - but it allows them to implement purely software-goverened voltage ranges to protect their accessories. But (lucky for us) it also makes it more tolerant to sticking the wrong thing in there - usually electronic devices just die if you get it even slightly wrong.
And good point about the inrush current.
keylight
Veteran
I'm thinking guyburns and g.l. probably have it right. The camera operates on a wide range of voltages. We don't really know what the high and low ends are. Next time I fully deplete the internal battery, I'll meter it before recharging. That would give us the bottom end.
keylight
Veteran
I wonder if it's possible (although maybe not all that desirable) to make a dc adapter that has a chip inside that would send a signal to the camera once the external battery hits 8.4v. The camera might shut off for a moment, but at least you would get some extra power.
Of course, we have no idea how the 2 extra contacts on the battery are used. It could be that the camera just checks to see if they are present (pass current through them to see if it completes a circuit). In which case, adding a little piece to bridge those two contacts when an external battery drops below 8.4v would be a fairly simple thing to do. I suspect it's a bit more complicated than that though....
I once hacked open a battery for my Nikon after it wouldn't hold a charge anymore, and the circuitry was pretty damn intimidating. Played with making an external power source using the old shell as an adapter, but could never get the right voltages out of the contacts. Someday when the GH2 battery stops taking a charge (hopefully after replacement batteries become widely available) I'll hack it open too......
g.l
Well-known member
You mean it would pretend to be an internal battery just as it hits the threshold? I think that would be tricky. The threshold is going to be a (small) voltage range, not just an exact value, due to inaccuracies/fluctuations/component tolerances etc. So even if you could do it, you may have to wait 'till the external voltage crosses the lower part of that range before the camera would accept it as an official battery, creating a temporary 'dead zone'. I think a firmware hack is a better bet to remove the battery protection completely.
I will run my bodies off 12V Li-on batteries (that way I can also drive my portable HDMI screens). I'll be using a DC->DC converter circuit to set a precise output voltage (I guess around 8.6V). They accept a wide range of input voltages, but keep the output voltage consistent. That's exactly what the bodies are doing of course.
keylight
Veteran
Yeah, something like that. It's an idea, but really not all that useful. Your idea however:
That is quite useful. I've been using one of these when I shoot long timelapse shots. It's really heavy but the power goes on and on.... It's something I'll probably want to get. Of course, I can always just plug the AC adapter into the 12v battery's AC outlet, but that's somehow a lot less elegant. Going from 12v DC to AC and then back to DC.
Are you making your own circuit or do you have a good source for something off the shelf? I found this but I'd rather have something single purpose and locked into one voltage.
Using a Ni-MH 12v + voltage regulator for an output of 8.6 V would be functional, efficient and safe?
Ni-MH 8.4 V versus NI-MH 12v + voltage regulator, pros and cons?
Batteries:
http://portuguese.alibaba.com/product-gs/nimh-battery-pack-with-12v-voltage-and-42a-maximum-discharge-rate-348402030.html
http://portuguese.alibaba.com/product-gs/nimh-f-7000mah-12v-rechargeable-battery-pack-203100850.html
I am Brazilian and I have little understanding of English, who helps me is the google translator, sorry for the mistakes and the lack of understanding.
I'm learning a lot here and want to ride my kit
Thanks.
Ni-MH 8.4 V versus NI-MH 12v + voltage regulator, pros and cons?
Batteries:
http://portuguese.alibaba.com/product-gs/nimh-battery-pack-with-12v-voltage-and-42a-maximum-discharge-rate-348402030.html
http://portuguese.alibaba.com/product-gs/nimh-f-7000mah-12v-rechargeable-battery-pack-203100850.html
I am Brazilian and I have little understanding of English, who helps me is the google translator, sorry for the mistakes and the lack of understanding.
I'm learning a lot here and want to ride my kit
Thanks.
Eugenio: The batteries you posted would have plenty of oomph. Then you'll need a regulator, and unless you have the technical knowledge to build one, you would require one that has 8.6 - 9.2 volts output, rated at 1.2 amps. Such an off-the-shelf device may be hard to come by, though I haven't looked into that yet. You may get away with a regulator rated at less amps, say 1.0 amps, but the Pansonic power supply does say 1.2 amps. The camera may not draw that much, but my guess is that under worst-case conditions the GH2 may draw up to 1 amp – and 1.2 amps allows a margin of safety.
I'm toying with the idea of experimenting with one of these:
http://focus.ti.com/lit/ds/symlink/ptn78000w.pdf
Costs less than $20 from places like digikey or RS Components. It provides up to 1.5 amps output, would require higher than ~11 volts input to give 8.6 volts output, ~90% efficient, and is easily adjustable with one resistor (see page 10 of the PDF). But building such a unit would require a certain amount of expertise.
I'm toying with the idea of experimenting with one of these:
http://focus.ti.com/lit/ds/symlink/ptn78000w.pdf
Costs less than $20 from places like digikey or RS Components. It provides up to 1.5 amps output, would require higher than ~11 volts input to give 8.6 volts output, ~90% efficient, and is easily adjustable with one resistor (see page 10 of the PDF). But building such a unit would require a certain amount of expertise.
Because the GH2 internally has a cutoff voltage that is probably around 6.6 volts, maybe even as low as 6.0 volts.
Not quite the bottom end, but it would be useful to know the battery voltage when you pull it out. The actual cutoff point would be difficult to measure accurately, because you would have to monitor the voltage at the GH2's power terminals as the voltage dropped, and note when it turned off. You might get an idea of the lower cutoff voltage by running the battery down so that the camera turns off, then pulling the battery out and measuring its voltage. But the problem is that the battery voltage will recover a certain amount -- it will immediately increase as soon as the load is taken off. i.e the battery volts will decrease… 6.8, 6.7, 6.6 … then the camera might turn off at 6.6, but by the time you pull it out it may have recovered to 6.9.
As a real example, I just loaded a Li-ion 860 mAh battery (4.03 volts unloaded) with 400 mA. The battery (not fully charged) dropped to 3.65 volts in about 30 seconds. I removed the load, waited 5 seconds, and the voltage had risen over that time to 3.92 volts, and still rising.
An interesting approach, but there is an easier way. My idea is to have a DC adaptor that fools the GH2 into thinking there is a battery in place all the time. The Chinese makers of the 3rd-party batteries have worked out what to put inside their batteries to fool the GH2. Now what they should do is manufacture a battery but without the chemicals. inside there would be a few components, and two wires leading from the power terminals to a socket on the rear for connection to the outside world. A battery without the li-ion; A DCC8 that does not cutoff at 8.4 volts.
I have asked the HK supplier who sold me a battery and charger to ask his supplier to make such a device. He has not responded yet. I think it's about time I sent messages to all the eBay sellers of 3rd-party batteries, asking them the same thing. But their English is not the best. Anyone here with the ability to write in Chinese?
If any of the Chinese manufacturers are reading this, here's how you do it.
1. Manufacture battery case without the chemicals, but with certain components connected to the T and D terminals to fool the GH2 into thinking it is a battery.
2. Mould a power socket onto the rear to which any battery of any chemistry from 12-32 volts can be connected.
3. Use this fixed 9-volt switching regulator (efficiency > 92%) between the power socket and terminals + and -.
http://products.cui.com/adtemplate_...tky=328060&subcatky1=521999&subcatky2=568080#. Cost ~$5 each in bulk.
4. Place ad on eBay: "Superior DCC8 replacement. Works by any voltage more than 12 volts. 95% efficient. Only $25. Shipping free"
2. Mould a power socket onto the rear to which any battery of any chemistry from 12-32 volts can be connected.
3. Use this fixed 9-volt switching regulator (efficiency > 92%) between the power socket and terminals + and -.
http://products.cui.com/adtemplate_...tky=328060&subcatky1=521999&subcatky2=568080#. Cost ~$5 each in bulk.
4. Place ad on eBay: "Superior DCC8 replacement. Works by any voltage more than 12 volts. 95% efficient. Only $25. Shipping free"
I guarantee you'll sell thousands and become rich!
Edited: A 7.2-volt switching regulator would be better than a 9.0 volt regulator as it would output the same nominal voltage as the battery.
Last edited:
That DC-DC adaptor has no technical information on the Amazon website, and I couldn't track down any. However, I did track down a similar looking device with technical information. This particular unit supposedly provides a regulated 2000 mA at various output voltages:
http://www.jaycar.com.au/productView.asp?ID=MP3038
Thanks for the information !
I'll look for an electronic technician to build my voltage regulator, fixed output of 8.6 V and 1.2 mah
If I find an electronic technician qualified to do this will be my salvation.
Buying at B & H three original batteries and sending to Brazil ..:
Three Battery: $ 60 unit
+
Shipping: $ 50
______________________
$ 230
+
Abusive tax: 78%
______________________
Total: $ 410
I'll look for an electronic technician to build my voltage regulator, fixed output of 8.6 V and 1.2 mah
If I find an electronic technician qualified to do this will be my salvation.
Buying at B & H three original batteries and sending to Brazil ..:
Three Battery: $ 60 unit
+
Shipping: $ 50
______________________
$ 230
+
Abusive tax: 78%
______________________
Total: $ 410
g.l
Well-known member
That's exactly what I'm working on, except I'm using the 3A version (PTN78060W) as I'm driving two bodies (stereo rig). I have my free samples from TI, but you need to supply some additional parts (2 caps & a resistor).
Similar simpler versions do exist on Ebay (everything included, just adjust a trimmer to set your output voltage). I have no idea how reliable they are, but they may be fine. They're called DC DC 'step-up' / 'boost' converters (smaller V in, higher V out), or 'step-down' / 'buck' (higher V in, smaller out). Make sure they handle your input V range (max & min charged state), and that you will input enough voltage for the desired output voltage (the step-downs typically need a bit more voltage going in than coming out).
You can check out my preferred 12V batteries in the 3D rig thread, they are cheap, small, cased, and can be charged just by plugging the AC adapter they come with in. And Li-ons are smaller/lighter than Nimh etc. I've got mine already, but I haven't been able to test them yet.
Last edited:
g.l
Well-known member
It's a good idea, but do we know that the body would accept an 'official' battery that puts out more than the official voltage? I think it's likely it will detect that as a dangerous situation (assuming a battery malfunction) and shut down.
... or (reading your post again), did you mean with a DC converter built-in?
g.l
Well-known member
I found these when I did my research too. They have 9V outputs - if 9V is safe (for longer periods) then they would probably work with 12V batteries. Lots on Ebay.
g.l
Well-known member
The step-down DC voltage converters typically need an extra 2 (or more) Volts in than they output. So chances are you need to input at least 8.5V + 2V = ~10.5V (maybe more). Also note that many batteries give out a higher voltage than rated when fully charged, and lower as they run out - so you need to take that into account too.
If the battery has a high enough mah (ma per hour) rating, sure
. The bundled battery is 1200mah @ 8.4V, which means 'you can draw 1.2A for an hour before it dies' (if you take less, it lasts longer). So that gives you an idea.Note that amps go down as voltage goes up, and vice versa. The formula: Watts = Volts * Amps.
So 1.2A (1200ma) @ 8.4V = (1.2 * 8.4) 10.08 Watts
So the equivalent A in 12V = 10.08W / 12V = 0.84A (840ma)
So for example, a 1200mah rated 12V battery will actually give you 1714mah if you convert it to 8.4V (more than the official battery). But you also loose around 5-10% in the conversion (depending on the efficiency of the converter), so it's more like 1600mah.
Last edited:
I managed to find the voltage regulator ptn78000w here in Brazil.
I do not have the least experience with electronics, I think of buying the components and find a professional to make adjustments and fit the puzzle.
Buy ptn78000w and make adjustments with a good professional is an alternative with an acceptable degree of certainty?
Or build a voltage regulator of the zero point is more reliable?
I'll get more information about the ptn78000w.