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Possible 130wh (8800mAh) DIY Bag Power for Cheap


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Okay, so I just wanted to through this out there to see that you all though. I have been looking for a good and less expensive than the NP-1 route to power the gear in my bag and have though of something interesting. But before I go trying something dumb and breaking my new toys, I thought Id post all about it here and see what you guys came back with. So here we go:

One of my deepest passions in life has always been photography and pretty much all areas of it at that. The area in particular that got me thinking was that of on location portraiture. Specifically the power sources photographers need and use to power profressional studio strobes. In my on location portraiture gear kit, I own a couple portable battery powered inverters that I use to drive my stobes. Now the part that go me thinking was the Li-Ion batteries that these come with (and can be purchased separately) and their voltage output and capacity.

Doing some reasearch I found that a standard and popular NP-1 style battery (in this case the IDX NP-L7S LINK) is a 14.6v, 4.6Ah (4600mAh) battery that yeilds 68Wh.

I found the following equation to help me with some simple calculations:

Wh = (mAh / 1000) * V

Inserting the specs from the IDX NP-L7S battery we get:

(4600/1000) * 14.6 = 4.6 * 14.6 = 67.16 which is approximately the quoted 68Wh

Okay, so I just ran that calc to check the equation and verify some values.

Now, the battery I found is a bit different shapped, but it offers the specs of 14.8v, 8.8Ah (8800mAh) yeilding what I calculate to be approx 130Wh. Heres the math:

(8800/1000) * 14.8 = 8.8 * 14.8 = 130.24 which is approximately 130Wh

Fine, so why go through all this trouble? Well, this battery I own is $89 and the charger, is $29. Thats a whole lot more appealing that the minimum of $200+ for an NP-1 battery and charger setup. And it fits nicely in the back pocket of a Petrol PS607 bag.

The Battery: LINK

The Charger: LINK

So what Im thinking now is this: the connection on this battery is a standard crimp on connection type thats pretty cheap. Ill post a link when I find one, I just cant remember what that dang things are called at the moment, plus Ive had a couple beers at this point which isnt helping. But making a simple cable from these two connectors to say the Sound Devices Bare Hirose 4-pin HR10-7P-4P Power Connector (Pins 1(-) and 4(+) from the SD manual) LINK should be no problem at all. Or even cheaper here: LINK. And just like that you have a power source that is roughly twice the run time of an NP-1.

Now the part Im having a bit of trouble with and that I hoping someone out there can help me out on is how do I wire this up to split the source so that I can power both a 702 and 302 from the same battery. Wiring two Hirose connections in parallel from the red and black connector (whatever its called) should do it right? At least thats what Im thinking.

Ive attached a few pics of the various parts, including the battery shown fitted nicely in the back pouch of a Petrol PS607 bag.

Now believe me, I know Im not the first to suggest some DIY battery combo, nor will I be the last. But the fact that this setup could potentially be cheaper and longer running than some other options makes it something at least to consider. Especially for me since I already own it! ;)

So, what do you guys think? Is it worth pursuing or am I just heading to blow up my 702?

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It should all work fine but you're killing me with all the math! If it puts out 12 vdc and you make safe and secure connections (parallel leads, + and -, to connect 2 devices shouldn't be a problem), you should be good to go. The price is right if it doesn't work out you haven't lost much. By not working out I don't mean to imply that you will damage your gear, highly unlikely, but even if you have done all the math you may find that you don't get the performance you are expecting.

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It should all work fine but you're killing me with all the math! If it puts out 12 vdc and you make safe and secure connections (parallel leads, + and -, to connect 2 devices shouldn't be a problem), you should be good to go. The price is right if it doesn't work out you haven't lost much. By not working out I don't mean to imply that you will damage your gear, highly unlikely, but even if you have done all the math you may find that you don't get the performance you are expecting.

Yea thats what Im thinking, just wanted to bounce the idea off the forum and see what people came back with.

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I've done the dumb testing for you:

I use one of these: LINK

It's designed for a RC helicopter, but can power my bag of a 744T, 302 and QRX for nearly a full day if I leave everything turned on. It's rated at 5000mah.

The caveat with using MY kind of battery is there's no internal balancing of the cells going on, so I connect it to a balancing charger. Seeing as you battery doesn't have an external balance connecter, I'd assume there would be some sort of internal balancing going on (the same as what happens in an NP-1 that isn't connected to a smart charger).

The only issue I think you might have is that the connector looks like it would come apart fairly easily if the two units (battery and inverter) aren't connected together, as they wouldn't be in your case.

Other than that, I'd say you're good to at least try it out...you're not going to blow up your gear, unless it can't handle 16.8v (the voltage this battery will output fully charged).

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I've done the dumb testing for you:

I use one of these: LINK

It's designed for a RC helicopter, but can power my bag of a 744T, 302 and QRX for nearly a full day if I leave everything turned on. It's rated at 5000mah.

The caveat with using MY kind of battery is there's no internal balancing of the cells going on, so I connect it to a balancing charger. Seeing as you battery doesn't have an external balance connecter, I'd assume there would be some sort of internal balancing going on (the same as what happens in an NP-1 that isn't connected to a smart charger).

The only issue I think you might have is that the connector looks like it would come apart fairly easily if the two units (battery and inverter) aren't connected together, as they wouldn't be in your case.

Other than that, I'd say you're good to at least try it out...you're not going to blow up your gear, unless it can't handle 16.8v (the voltage this battery will output fully charged).

Awesome. This is the support I was hoping for. I should be good with the voltage as itll be powering a 702 and 302 which will accept 10v - 18v on the Hirose DC in. So its the same setup as your doing just a different battery. And yea Ill have to watch that connector. Ill have to find a way to route it with the least amount of stress on it.

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Other than that, I'd say you're good to at least try it out...you're not going to blow up your gear, unless it can't handle 16.8v (the voltage this battery will output fully charged).

I missed the part about 16.8 volts --- that would be a real concern since that is over the acceptable voltage range for quite a number of devices. I would really take a close look into that part of it before hooking up any of your gear.

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I missed the part about 16.8 volts --- that would be a real concern since that is over the acceptable voltage range for quite a number of devices. I would really take a close look into that part of it before hooking up any of your gear.

Jeff, any device that can handle being powered by an NP-1 can handle 16.8v, as it's basically the same battery. In real-world use, the output voltage of the battery drops under load anyway, I generally see around 16.2v off my battery at the start of the day.

The other thing that this battery probably doesn't have is a LVC or low voltage cutoff. When a lithium cell gets discharged under 3v per cell (3x4=12V) for your pack, damage will occur the cells, they will go out of balance and could catch fire/explode the next time they are charged.

An NP-1 (or similar battery) has a LVC to prevent the battery ever being discharged this far - it simply shows the battery as 'flat', and protects it from being discharged any further. There are some LiPo, Li-ion, and LiFePo4 packs that have a PCB or PCM installed, these basically cut the output once it's reached below a certain voltage.

My battery doesn't have an LVC either, so I have a BDS with a RM meter, which shows me the voltage output of my battery at all times. Once it starts to get under 13V, i know it's time to switch it out. I'm re-doing my bag power this year to use newer and more stable LiFePO4 chemistry, which also has a lower maximum output voltage (14.4v as opposed to 16.8v) which might tax the switching power supplies in all my gear a little less.

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Most devices we use operate in the 10 to 18 volt range. I use a battery similar to soundslikejustin, and it charges fully up to 16.8 volts. No problem with Nomad plus four Lectro 211 rx, and a D-4 tx. It does have the LVC however. My only concern is that I have a balance charger but my batteries don't have the balancing lead, and I think their run time is slowly getting shorter and shorter. It could be too that this latest combination of gear just pulls more juice.

I use a Traxxas connecter http://traxxas.com/g...rrent-Connector adapted to a female coaxial to adapt to my BDS box. Its a much sturdier connector than the one you show benr. You could easily change out the connector out if you didn't think it would be sturdy enough.

I'd be interested in hearing about that other battery chemistry when you get it soundslikejustin.

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Wait, where did the 16.8v value come from? The IDX NP-1 outputs 14.6v and the battery Im considering using outputs 14.8v.

The other thing that this battery probably doesn't have is a LVC or low voltage cutoff. When a lithium cell gets discharged under 3v per cell (3x4=12V) for your pack, damage will occur the cells, they will go out of balance and could catch fire/explode the next time they are charged.

An NP-1 (or similar battery) has a LVC to prevent the battery ever being discharged this far - it simply shows the battery as 'flat', and protects it from being discharged any further. There are some LiPo, Li-ion, and LiFePo4 packs that have a PCB or PCM installed,

Since the 702 displays and reads the voltage from its power source, I wonder it itll take care of shutting down once the power gets too low. If not it can be watched on the display and could be monitored and shut down when it reads too low.

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Most devices we use operate in the 10 to 18 volt range. I use a battery similar to soundslikejustin, and it charges fully up to 16.8 volts. No problem with Nomad plus four Lectro 211 rx, and a D-4 tx. My only concern is that I have a balance charger but my batteries don't have the balancing lead, and I think their run time is slowly getting shorter and shorter. It could be too that this latest combination of gear just pulls more juice.

I use a Traxxas connecter http://traxxas.com/g...rrent-Connector adapted to a female coaxial to adapt to my BDS box. Its a much sturdier connector than the one you show benr. You could easily change out the connector out if you didn't think it would be sturdy enough.

While that connector does look much better, the one in the battery I am considering is not removeable without disassembling the battery and those you posted are not the same as these ones unfortunately.

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Have you seen any information revealing that the charger will automatically shut off once the battery is fully charged? I usually charge when i'm asleep so having to manually unplug once its done isn't an option for me. That's the only thing holding me back right now from doing my custom LiFePO4 battery setup in the other thread here.

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the 16.8v comes from the highest voltage the battery produces. All batteries have a voltage range, from full to empty, and a nominal voltage. A '14.8v' Lithium-Ion or Lithium-Ion-Polymer battery outputs between 16.8v when full, and 12v when empty. The middle (or nominal) voltage in this range is 14.8v. This is due to the chemistry of the individual cells in the battery.

The data sheet for the IDX NP-1 shows a maximum output voltage of 16.8v, as expected.

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the 16.8v comes from the highest voltage the battery produces. All batteries have a voltage range, from full to empty, and a nominal voltage. A '14.8v' Lithium-Ion or Lithium-Ion-Polymer battery outputs between 16.8v when full, and 12v when empty. The middle (or nominal) voltage in this range is 14.8v. This is due to the chemistry of the individual cells in the battery.

The data sheet for the IDX NP-1 shows a maximum output voltage of 16.8v, as expected.

Gotcha.

Found some more info on the battery. Looks like it does have a cut off voltage of 11v as well as a fully charged voltage of 16.6v

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Most devices we use operate in the 10 to 18 volt range. I use a battery similar to soundslikejustin, and it charges fully up to 16.8 volts. No problem with Nomad plus four Lectro 211 rx, and a D-4 tx. It does have the LVC however. My only concern is that I have a balance charger but my batteries don't have the balancing lead, and I think their run time is slowly getting shorter and shorter. It could be too that this latest combination of gear just pulls more juice.

I use a Traxxas connecter http://traxxas.com/g...rrent-Connector adapted to a female coaxial to adapt to my BDS box. Its a much sturdier connector than the one you show benr. You could easily change out the connector out if you didn't think it would be sturdy enough.

I'd be interested in hearing about that other battery chemistry when you get it soundslikejustin.

A LVC on a battery generally only protects the ENTIRE pack going under voltage, you could have a few worn out cells that are going lower than they should. Then on re-charge, you would be pushing the good cells over their UVC. It's difficult to tell what the individual cells are doing without a balance lead.

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Have you seen any information revealing that the charger will automatically shut off once the battery is fully charged? I usually charge when i'm asleep so having to manually unplug once its done isn't an option for me. That's the only thing holding me back right now from doing my custom LiFePO4 battery setup in the other thread here.

Looks like it does:

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Have you seen any information revealing that the charger will automatically shut off once the battery is fully charged? I usually charge when i'm asleep so having to manually unplug once its done isn't an option for me. That's the only thing holding me back right now from doing my custom LiFePO4 battery setup in the other thread here.

Most 'smart chargers' and even some rudimentary ones can detect the end of charge voltage and stop the charging process. Some then apply a 10ma or so trickle charge, some don't. Check the specs on the charger, and see if it terminates the charge, or just changes an LED to indicate the battery is at full voltage. This is the difference between being able to leave the battery on charge while you sleep, or not.

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More info on the battery.

The manual is actually pretty informative. Heres a link to it if any of you want to look it over: LINK

It doesn't say if the cut-off is inside the actual battery, or within the main unit (inverter section). This may mean that it is up to the inverter section to cut the battery off when it is empty. Because you can charge directly into the battery (you don't have to go through the inverter), I'd say there's at least some circuitry inside the battery itself - for balancing (hopefully), and possibly in the charger (my initial thought was that it might just be a 'dumb' 12VDC power supply). So you're probably protected while charging, we just can't be sure that the battery has a LVC in it...

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It doesn't say if the cut-off is inside the actual battery, or within the main unit (inverter section). This may mean that it is up to the inverter section to cut the battery off when it is empty. Because you can charge directly into the battery (you don't have to go through the inverter), I'd say there's at least some circuitry inside the battery itself - for balancing (hopefully), and possibly in the charger (my initial thought was that it might just be a 'dumb' 12VDC power supply). So you're probably protected while charging, we just can't be sure that the battery has a LVC in it...

Very true... Hmmm... Might have to shoot an email to them and/or check their forums. Ill post back with what I find.

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Okay, found the connector! Its called an Anderson connector! I knew it was something like that, the techs I work with have told me about it before I just couldnt remember. Here is the data sheet for it, just have to figure out where to get them now. LINK I cant seem to find them on Digi-Keys website. Although here is a drastically overpriced set: LINK

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And here they are at good ole Mouser

Anderson Connectors: LINK

Hirose 4-Pin Connector: LINK

I just want to point out that if you order these from amazon, you will actually save money. You will pay a minimum of 7 dollars shipping from mouser, amazon shipping is free (at least if you have amazon prime). If you didn't notice the amazon one is 4 red connectors and 4 black.

I think i'm going to try this setup.

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I just want to point out that if you order these from amazon, you will actually save money. You will pay a minimum of 7 dollars shipping from mouser, amazon shipping is free (at least if you have amazon prime). If you didn't notice the amazon one is 4 red connectors and 4 black.

I think i'm going to try this setup.

That might be true for the Anderson connectors, but since I didnt find the Hirose connectors anywhere on Amazon, you might as well get them both from Mouser.

And add a bit of 20AWG wire too and youre set.

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" some LiPo, Li-ion, and LiFePo4 packs that have a PCB or PCM installed, "

most do.

as stated previously, Lithium battery charging is a complex process, requiring a lot of electronics, especially in the battery pack (even the iPower 9V !!)

If IDX could reasonably lower the price of their products significantly, they would sell a lot more; they are not keeping their prices unnecessarily high, and follow the rule: generally speaking, you get what you pay for.

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