First draft of external ML battery power -

my stand arrived yesterday heres my studio set up because i have a smaller zoom so i can move in quickly for head shots

Max Iso wrote:

Funny you mention those bc i had seen the packs last week to house them. 3.7v right? The housing fitted two which worked out to a perfect 7.4v.

Li-Ion batteries generally have a 3.7v nominal voltage. Most 18650 batteries have a maximum capacity of 2,200mAh to 2,2600mAh.

The largest capacity batteries are going to top out around 2,900mAh. They'll be made by Panasonic, LG, or Samsung.

The only problem was they were only up to 5kmAh if i remember, about the same capacity as 3 OEM camera batteries for my G9.

If the enclosure can only hold 2 18650 cells, it is impossible to have a capacity of 5kmAh.

To get to a nominal 7.4v, the cells need to be in series. Every additional cell in series will increase the voltage, but not the capacity.

As an example, say you have 2 18650 cells with 2,500 mAh capacities. If you put them in series to get to 7.4v, you'll only have 2,500 mAh. To increase that, you'll need to add cells in parallel.

So banks are not accurate? Can they legally do that?

Who is in charge of checking to make sure advertised capacities are correct?

I tested a bunch on Sony NP-FW50 batteries, and it was laughable what some third party "manufacturers" tried to get away with. They were at 2/3 to 1/2 the capacity advertised.

After cutting the plastic housing off, the cells inside were labeled at what I would have expected to see based on the testing.

Isn't it possible they just have 2 in series and then two sets of that in parallel for double capacity? Or 3 sets for triple?

Yes, you could have a 2S3P (2 in series, 3 in parallel), 4S10P (4 is series, 10 in parallel), or other configuration.

Reading a primer or watching intro videos on DIY power walls or e-Bikes will be quite helpful to you. Learning the basics is easy. By doing that you'll have an easier time getting a solution that's good for you, as well as being reliable.

The 2 RavPower batteries I tested were close enough to their advertised capacity that I would be fine buying their batteries in the future.

I have a pair of 16750mAh RavPower banks and they charge a phone at least 3 times and have charge left, that puts them well over 10k right?

16750mAh / 2250mAh = 7.44

16750mAh / 2500mAh = 6.7

If your power bank looks like it can hold 6-8 18650 cells, the rating is likely close to accurate.

However, you need to keep in mind the voltage you plan to use. The battery bank is likely rated at 3.7v.

To get to the 5v required for USB charging, a boost converter is used. It isn't perfectly efficient, and you can tell this because it will give off heat.

If you double the voltage requirement to get to a nominal 7.2v, the 16750mAh would be cut down to 8,375mAh, before you take into account the loss from using a boost converter.

Max Iso wrote:

I already have a pair of 16kmAh power banks and they are fairly solid, similar in weight to one of my flashes with batteries installed. My plan is to go even bigger (maybe a 25kmAh to 50kmAh model) when i decide the final design but that weight isn't something i want on top causing so much imbalance.

The use of "kilo" and "mili" units together hurts my eyes. Even the use of the "mili" for figures of more than one thousand seems wrong to me.

Whats wrong in write 16Ah instead of 16kmAh?