RunRyder RC
WATCH
 1 page 112 views POST REPLY
🏠Home💠RC Main Discussion › 5600 MAH/7.4 volt li ion battery
04-27-2020 06:55 PM  29 days ago
Topic Vote1Post 1
7379df

rrApprentice

Branson,USA

MyPosts All Forum Topic
5600 MAH/7.4 volt li ion battery
Hey guys, Just curious what to replace my old Troy Built Models LI ION 5600 mah/7.4 volt batteries with ? All my bat trays are set up for the flat pack and rectangular stack. Anyone have any ideas where to point me ? Thanks !
BTW, I uses these for my Jet and my gasser Helis.
SHARE  PM  EMAIL  GALLERY  Attn:RR  Quote
04-27-2020 06:58 PM  29 days ago
wjvail

rrElite Veteran

Meridian, Mississippi

MyPosts All Forum Topic
💎Sustaining Member
Do you actually need 5,600mAh capacity? A lot of times these larger packs are used so that current draw doesn't exceed what otherwise might have been too much for a 2,800mAh pack. Do you use that much capacity?"Well, nothing bad can happen now."
SHARE  PM  EMAIL  GALLERY  Attn:RR  Quote
04-27-2020 09:56 PM  28 days ago
7379df

rrApprentice

Branson,USA

MyPosts All Forum Topic
Probably not.. but I have used those for years and someone else back in the day recommended them... so I have always used them. On the jet, one is used for turbine power only, and the other pack is used for servos and both are 5600 MAH. I can get several flights from these as well. So most now are using 2800 MAH ? Are there any companies even selling Li ions ? Thanks for your time and help.
SHARE  PM  EMAIL  GALLERY  Attn:RR  Quote
04-28-2020 12:36 AM  28 days ago
wjvail

rrElite Veteran

Meridian, Mississippi

MyPosts All Forum Topic
💎Sustaining Member
The short answer to your question is that I think a lot of guys use Fromeco batteries. I used to use them a lot myself. I have packs that must be 10 years old and are still safe to use. The people there are helpful and will certainly get you some quality batteries. https://fromeco-scale-avionics-llc....on-battery-line

The longer answer is that you can pretty easily make your own packs. I hope we can keep this thread going, but.... a lot of what we might discuss was just covered in this thread -> https://www.helifreak.com/showthread.php?t=859433 There is a lot of good information there. I posted a few thoughts starting around post #35.

I'll be waiting to hear other people's thoughts.
"Well, nothing bad can happen now."
SHARE  PM  EMAIL  GALLERY  Attn:RR  Quote
04-28-2020 03:38 AM  28 days ago
Rojoalfa

rrKey Veteran

Punta de Mata, Monagas-Venezuela

MyPosts All Forum Topic
/
/

5600 mAH... Why?

I have a rule of thumbs for that.

Flights = (CAP/2) x 70%/(consumption per flight)

For example:

Cap = 5600 mAH
Consumption per flight = 250 mAH
My Average for raptor 50.
For my spectraG, 300.
For my hirobo 30, 150
For my fury 91,300.

Flights = (5600/2) * 0.7/250

Flights = 7.8

So, with a battery pack of 5600 mAH, my raptor 50 may have 8 flights without charging.

That is why 2500 mAH is a good choice for class 50 helicopter.
They give you 4 flights.

That is why is important to measure consumption for your battery pack every time you charge. With this information, I can calculate consumption per flight for each helicopter.

For example, after 4 flights, I charge the battery pack.
It gets aprox. 900 mAH.
So, 900/4= 225 mAH.

Follow your own calculation.

/
Saludos cordiales,
SHARE  PM  EMAIL  GALLERY  Attn:RR  Quote
04-28-2020 03:53 PM  28 days ago
wjvail

rrElite Veteran

Meridian, Mississippi

MyPosts All Forum Topic
💎Sustaining Member
Rojoalfa Flights = (CAP/2) x 70%/(consumption per flight)
If I'm reading that right, you are suggesting using only 70% of 1/2 the pack?.?. So if someone installed a 4,000mAh battery, you calculate a usable capacity of 1,400mAh?

I can't say this is wrong but I will say it is very conservative. Some of my larger helicopters use about 700mAh per flight and I routinely fly 4 flights. I have zero issues with pulling 2,800mAh out of a 4,000 mAh battery. In fact, if it weren't for the voltage sag under load, I'd be comfortable using much more of the pack.

It is certainly safe to use your calculation. You won't damage anything using this calculation. You are just leaving a lot of capacity in the pack.
"Well, nothing bad can happen now."
SHARE  PM  EMAIL  GALLERY  Attn:RR  Quote
04-28-2020 04:23 PM  28 days ago
Rojoalfa

rrKey Veteran

Punta de Mata, Monagas-Venezuela

MyPosts All Forum Topic
/
/

I like your answer.
This is the second time I refer my rule of thumbs. It is not always well understood.

We can't use Half of the capacity because it is below 3.7 volts.

4.2 volts is 100%
3.7 volts is 0%.

In my rule of thumbs, I use 70% of real capacity, so the remanent is 30%. That means 3.8 volts remaining on battery pack when got exhausted.

I fly my gadgets and at the end of the day, my battery packs are at least with 30% or more.

Of course, you can use 80%, even 100%, but that it depends on health of your battery packs.

I am happy because it is the first time someone like you talk tecnically on this matter.

I got this rule of thumbs, gattering information on how much mAH your battery pack gets after some flights...

If you discharge to 0% (3.7 volts) your packs for example, 5000 mAH pack, By the time you charge this battery, it is going to get 5000/2, 2500 mAH.

/
Saludos cordiales,
SHARE  PM  EMAIL  GALLERY  Attn:RR  Quote
05-01-2020 02:17 PM  25 days ago
wjvail

rrElite Veteran

Meridian, Mississippi

MyPosts All Forum Topic
💎Sustaining Member
Rojoalfa We can't use Half of the capacity because it is below 3.7 volts.

4.2 volts is 100%
3.7 volts is 0%.
I wonder about the initial assumption that 3.7v is a practical cutoff.

Your rule of thumb would be safe, if not conservative, for a LiPo being used as the main battery of a helicopter or plane. In these applications current can be (very) high and LiPos really don't have a lot of capacity below 3.7v/cell.

What's being discussed here is using LiIon batteries to power the receiver and servos. In this application batteries are not stressed as hard and LiIon cell show good performance all the way down to 2.5v/cell.

Yesterday I had a reason to put together a 2 cell pack of 21700 cells. The cells I was using are rated at 4,000mAh and 35 amps continuous. After assembling the back I ran a few cycles through it to confirm it was performing as expected. Below is a screenshot of the last cycle before I put this pack in service. Because so much resolution is lost in the process I've taken the liberty of marking the 3.7v, 3.0v and 2.5v points on the plot.

-- The red line is pack voltage.
-- The purple line is capacity.
-- The very thin line is actually two lines and is the individual cell voltages.
-- The green line is current (7amps).

A 7 amp discharge was chosen as it is about what I calculate my MKS servos draw during a typical flight. While the cells are rated at 35 amps, some of the other components in the flight pack are only rated at 10 amps. Testing above 7 amps is not as valuable since other components become the limiting factor.

Looking at the graph you can see there is a considerable amount of usable capacity below 3.7v/cell. While I don't recommend it, there is usable capacity below 3v/cell. At 3v/cell HV servos begin to lose performance and a stalled servo or some other current spike could draw the pack voltage down further than I care to see.

"Well, nothing bad can happen now."
SHARE  PM  EMAIL  GALLERY  Attn:RR  Quote
05-02-2020 12:50 AM  24 days ago
Rojoalfa

rrKey Veteran

Punta de Mata, Monagas-Venezuela

MyPosts All Forum Topic
/
/

You are correct.

I develop this rule base on battery pack behavior of my trex600E.

Later on, I begin to use this approach with my battery pack onboard working primarily with regulators.

I will take your report into consideration.

The first barrier,
3.7 volts for high drain application.

Then 3 volts for normal drain.

/
Saludos cordiales,
SHARE  PM  EMAIL  GALLERY  Attn:RR  Quote
WATCH
 1 page 112 views POST REPLY
🏠Home💠RC Main Discussion › 5600 MAH/7.4 volt li ion battery
 Print TOPIC  Make Suggestion 

 3  Topic Subscribe

Tuesday, May 26 - 8:55 pm - Copyright © 2000-2020 RunRyder   EMAILEnable Cookies

Login Here
 New Subscriptions 
 Buddies Online