Mustangdude

Hi, I'm new to flying and have a basic question.

ZOHD Drift FPV with 3500ma ZOHD battery, Flysky FS-i6.

My first charge up and use went for 45 minutes, however the transmitter battery indicator showed the plane was still at 100%.

That's just before the plane got gutless and fell out of the sky.

Question: How do I know the battery is getting low?

Thanks,

Jim

See my short flight...I kill a tree.

firemanbill

Fly it for a few minutes timing it with a stopwatch or timer on your transmitter, land and check the battery, I never run mine below 30%. After a few flights you can get an idea of how long you can fly to get down to that point.

Running a battery all the way down to LVC will ruin a battery very quickly.

quorneng

Those words on their own would mean the battery in the transmitter not the battery in the plane, unless of course you have telemetry measuring the plane's battery voltage in the plane and transmitting that information back to the transmitter.
With out telemetry as firemanbill suggest the only safe way is to fly for a specific time with a fully charged battery and then use a battery capacity checker to find out how much you have used. From that figure you can work out how much longer it is safe to fly but always keeping 30% in reserve to be kind to the battery..
A 45 minute flight time would be about the maximum you could expect and it likely took the battery too low so my advice would be to keep to 30 minutes max.

Mustangdude

Ok, so I should take no notice of the battery icons showing the capacity of the plane and transmitter, it also shows voltage for both plane and transmitter too but I didn't take alot of notice of what they were at any stage.

Would a multimeter be ok as a battery checker? Is the 30% measured in volts?

Thanks for your replies.

solentlife

mmmmmm Guys .... he's got RX voltage showing - NOT motor voltage ...................

'Mustangdude' .......... I think you have confused the two voltages you have on an electric model. You have the usual 5.0V from BEC to the Receiver ....... that will stay 5V literally till the battery dies ... the second is the main battery power to motor which in usual use varies from about 3.5V up to 4.2V per cell. (3.5V is about as low as you want to go IN FLIGHT ... you better be lining up to land, 4.2V is max charged on a standard LiPo cell).

OK as others say - you need to measure your packs condition as soon as you land ... NOT 5 - 10mins later. As soon as you land .. measure the voltage before pack rests. You need to see WORST value. Packs recover when they cool ... can be 0.2 .. 0.3V per cell.

Here's a table that can help you (based on single cell)



As above .. with a typical moderate machine - you could land on 3.5V and then once pack has rested probably see cell voltage back up to about 3.7 - 3.8V .... personally I storage at 3.75V (Mallory Tech advised me on that ... ).

quorneng

Mustangdude
Tx voltage is probably reasonable. The Rx is also probably correct but it is the voltage at the receiver not the LiPo itself. The receiver voltage is kept at a regulated 5V almost regardless of the LiPo voltage.

A LiPo battery voltage does fall with degree of discharge but it is small and not linear. You would need a multi meter accurate to 1/100 of a volt and more to the point know what the voltage should actually be for a particular state of charge.
For this reason battery checkers really only give an indication of charge but are not highly accurate..
In addition LiPo have a habit that their cells do not discharge to exactly the same level hence the need of a balance plug which makes a connection to each cell individually.
By far the best way to determine what is level of charge was is for the charger to record how much (mAhs) it has put back in to fully charge it.
In other words if it put back in 900 mAh to fully recharge an 1000 mAh capacity battery you had discharged it to 90% which is to low for a good LiPo life.
To make matters even worse a LiPo capacity slowly declines as you use it. You are doing well to still have 80% capacity after you have used it more than100 times.
So the advice is when it is new, or reasonably new, fully charge (always balance charge if it is multi cell) and fly for a relatively short measured time and see how many mAh it take to fully recharge it. You then have the information to work out a maximum 'safe' flight time.
Finally a LiPo should not be left fully charged for more than a day or two. If you are not going to fly again bring the LiPo down to 'storage' level, which is 3.8V in each cell, using the 'storage' option on the charger. A that level the LiPo will not deteriorate of many months.
What LiPo are you using and what sort of charger?
Edit
I was writing this as solentlife replied

Mustangdude

Thanks guys, that's all stuff I should have researched before I flew so I'm kicking myself a bit.

I haven't balance charged it yet either....I've read everything from you two and saved it. Thanks for your help.

Mustangdude

I just did a 20 minute flight with a possible damaged LiPo and balance charged it.

Being that it's a 3500 ma 2s shouldn't the charger reflect that? Whats the 1450 about?

quorneng

If you previously took the battery to almost empty in 45 minutes then a 20 minute flight is 44% as long. it was fully charged so putting back 1450 mAh (about 41%) is about right.
The duration in a plane like yours is very dependent on hour much throttle you use. I would expect it can fly on about half power. You will get used to acceptable flight times.
Flying in the wind tends to use more throttle so you have to reduce the flight time appropriately.
Are you aware that if you press the "Inc" button at any time during the charge it will show the individual cell voltages. Press it again and it returns.

The fact your battery voltage is showing 8.39 indicates that both cells have not achieved 4.2V. A balance charge might cure that.

Mustangdude

Thanks Quorn, I may have damaged the battery because that pic was a balance charge. I've only charged it three times, twice unbalanced and once balanced.

I'll try the INC button for sure.

Thanks for clearing alot of my problems up.

Jim.

ron_van_sommeren

The LVC in your motorcontroller protects your flight battery from getting ruined. Although it's a safe practice to stop a bit before the has to LVC kick in.

Some well-structured reading for rainy/windy days. Will save you, and us a lot of questions. Notably the 'what went wrong?' kind of questions Will also prevent you from burning up several controllers and/or motors and/or battery:
E-flight 101 by RCG member Ken Myers, will at least save you a ruined LiPo (or worse!), a burnt motor and a fried ESC:
The Ampeer
→ Articles: Electric Power Basics (Ken Myers)
Table of Contents, a.o.

• Recommended First Purchase - Power Meter & How to Use it
• About Chargers & LiPo Batteries
• Power Lead Connectors and Wire
• Brushless Electronic Speed Controls (ESC) Basics, LVC and BEC
• Motors for Electric Flight, kv, Timing, Efficiency, Props

E-flight 102
The Ampeer
→ Articles: Everything youw wanted to know about e-flight (Ed Anderson)
Table of Contents, a.o.

• What You Need To Know About Receivers
• Battery Basics, Battery Chargers
• Ampères Versus Volts Versus C
• Electronic Speed Control (ESC) and Low Voltage Cut Off (LVC)
• Sizing Power Systems for Electric Airplanes, Prop Versus Amps
• What Do the Kv Numbers On Motors Mean?
• Who Needs a Wattmeter/Powermeter?
  (Everyone! But don't buy one if you plan on sponsoring motor and ESC manufacturers RvS)

solentlife

OK ... lets break this down ...

Your Charger display shows :

Charged Fully
0.0A = charge rate
8.39V indicates its a 2S battery.
CHG = Charge mode only
104.11 = minutes on charge
01450 = mA's put back into battery in total.

You have a 3500mAh 2S pack. The maximum mA's to a safe level discharge is about 2800mAh's ... leaving at least 700mAh's in the pack.... you cannot and should not try to use 100% of the pack ... 70 - 80% is a level you should not exceed.

OK - lets put some items to bed ...

1. Strong advice to NOT just use CHARGE mode ... use BALANCE MODE ... that way you make sure each cell is charged properly. If you use CHARGE mode - then at least connect balance lead as well - that at least can stop one cell being overcharged - but it will NOT balance the pack.
2. LiPo cells actually do not lose capacity as much as some think ... yes they do physically change - electrolytes reduced transfer back to charged state ... but the fact is that cells have apparent loss of capacity because they cannot deliver their full mAh's as they get older. They tend to get warmer .. their Internal Resistance has increased - making the voltage drop higher. As it gets worse - the voltage drop is enough to reduce power output to too low a level. If you take that battery .. let it sit for a few minutes then check it - you will see it has recovered and looks like it should work OK - but reconnect and try fly .. voltage drop is high again and it apparently is discharged .. rest it and voltage recovers.
3. I'm not of the mA's IN brigade as chargers only calculate that number from the time vs charge rate that the charger does and that can be an averaged calculation. Its simple maths nothing else. Voltage is of course a poor measurement standard as well - but its the only practical way to do it, we don't have facility to cycle measure batterys - that's measure mA's out and mA's in via cycling. Yes some chargers have cycle mode - but again its not laboratory standards - its simple maths again.. The LiPo checker or Wattmeter is a simple practical 'good enough' tool to use especially in field. The main point is to not over-discharge a lipo.

Summary :

1. Charge using Balance Mode.
2. Do not leave LiPo's higher than storage for more than a day unless absolutely necessary
3. Set ESC LVC at reasonable level - I use 3.2 - 3.3V ... and SOFT cut-off. That means I can close throttle - re-open throttle to get at least a few sec's motor to land. BUT I try not to get that low !!
4. Get a wattmeter - this must be one of the most important tools in our kit.
5. DO NOT try to fly with partial discharged battery. We all do it at times - but it really is taking a risk ...
6. Always let batterys cool down before recharging or connecting to put to storage level. The voltage levels are not correct when heated - second you are damaging the cells.
7. Always check used batterys level once rested and return to storage as soon as possible.

OK - storage voltage ...

Most chargers are set at 3.85V per cell for storage. This is generally regarded as the highest value in range. Lowest value is 3.7V. According to an old pal of mine who was Senior Tecgh at Mallory battery's - the 3.85V setting is probably a result of decision to stay in storage range - but try reduce charge time. The 3.7V is according to him - the better figure - but then your charging time is increased. His advice to me as compromise was to use 3.75V.
Each person of course decides for themselves and if using a standard LiPo charger - then you are pretty well fixed at 3.85V ... unless you have a programmable set.
I use the 3in1 Discharger from MyRC-Mart and I can set the storage level on it at 3.75V. I only use a charger if I have a lot of batts to discharge.

solentlife

Sorry but that pic clearly shows CHG ... which is NOT a balanced charge mode. As Quorn says - your cells are not balanced because the voltage shows 8.39V. What happens in charge mode and balance connected - the charger detects when any cell hits 4.2V and then shuts off. Only when using Balance mode will charger bring ALL cells to 4.2V and then shut off.

Note : During BALANCE MODE ... it will be seen that display often shows 0.0A rate once battery is near full ... this is because charger is now bleeding off high voltage from one or more cells to bring down to level of lowest cell ... once that is done - Amps start showing again charging ... it can repeat this many times until all cells reach 4.2V.

Use of the INC button as Quorn indicates - will show this situation of different cell voltages.

Mustangdude

Thanks Solent, The china instructions are crap but I got it now. All balanced and good. Plus I'm a typical bloke who should read instructions more closely.

quorneng

Just as confirmation of what solenlife says I checked the cell voltages of a brand new 3 cell battery as delivered. They were all identical at 7.74 Volts.

solentlife

Hi Q ..... 7.74 ? You mean 3.74 ??

I just checked 2 new 4S I rec'd ... all cells were 3.77 - 3.78 .....

quorneng

Oooops!
Of course 3.74V
Actually an interesting exercise as it is a 850 5s (there is no such thing at HK) made up from a 2S and 3S.


Needs care and attention with the soldering!

solentlife

Joining packs ..............

Care when soldering - I can agree there ... I near had heart attack one time ... when I had a brain fade moment ... I needed to change a plug on a lipo ... so without thinking grabbed the clippers and snipped through BOTH leads !! WOW what a display ! Amazing - that battery years later was still in use ...
Hate to admit this as well ... I had a Deans gripped in the vice ... soldered one lead ... touched the other to solder .. BHAM !! yep - I had gripped via the metal tabs !!

Another safety matter - I cannot understand why Soldering Boards to help hold plugs while soldering are METAL ? I made one from a block of wood so the plug can never short ...

firemanbill

I think anyone who has been using electrics for any amount of time can relate! I have my fair share of "enlightening" moments. LOL

Mustangdude

One last question.

Now I've been made aware of the LiPo battery potential volatility I've ordered some safe storage bags for my RC batteries.

Then I look around at other lithium powered things at home and wonder whether they should be stored differently.

Like a lithium jump starter pack, DSLR camera batteries, LiPo drill batteries, torches and even our mobile phones. Why do we treat RC batteries differently with regards to safe storage.

I leave my mobile phone on charge all night without giving it a thought and my starter pack has no storage charge option, it's full all the time

Thanks,
Jim.

ron_van_sommeren

'We' 'rape' batteries: much high(er) charge and discharge currents, deep discharge, deep landings a.k.a. crashes.
'We' also make mistakes setting charge current, setting battery type (different charge methods), and tend to under-estimate discharge current.
Every now and then 'we' let the poor things collide with terra firma at speed.
The more powerful/energyful home batteries, e.g. bicycle packs, have a BMS, Battery Management System, in the battery pack.

LiPo's are prima donnas, LiPoFe4 cells are way more robust, albeit with lower power and energy density. Some for specific power and energy.

ron_van_sommeren

Increase in current with one or two cells added, simple table - RCG

The 'full' story.
Current and power drawn are proportional to

• pitch
• #blades
• voltage² respectively voltage³
• Kv³
• diameter⁴

So even a small change in setup can result in quite an unexpected increase. Always measure current with a watt-meter (howto/tips)in a new or changed setup.


Expensive examples.
Going from 2s to 3s, a 50% increase, would (3/2)²=2.2fold current, more than double, 120% extra.
A 25% increase in velocity konstant Kv would (1.25)³=2fold current, 100% extra.
A mere 10% increase in diameter would (11/10)⁴=1.1⁴=1.4 fold current, 40% extra.


Extreme examples.
Doubling voltage would, 2²=4, four fold current.
Doubling Kv would, 2³=8, eight fold current.
Doubling diameter would, 2⁴=16, sixteen fold current.

solentlife

Its the Human Factor.

Dunno about your computers / phones etc - but most do not charge right up to max .. they don't stress the packs so much. When you are using your laptop / smartphone - you are actually discharging it even if plugged in - albeit at a very very low rate ... the BMS sees to that.
Emergency starter batterys are often not LiPo as we use in models but a different Lithium format and often metal or hard cased.

Model batterys as we use are 'soft cased' and without management systems built in ... except those for example in DJI or various drones ... or hard case as used in cars / boats.

Lithium batterys such as LiFe and the base LiIon are now appearing in recreational vehicles such as caravans and boats ... but with BMS additions.