LiPo RX Batteries & Monitoring

[YOUNG GUN]

Hi All,

Just in the process of ordering bits..

For my new Heli - i've decided to have a seperate RX LiPo - rather than just putting a UBEC on the flight battery.

The RX Lipo i've gone for is a 2S 2,100mah LiPo - the perfect physical size for what i want...

I have got a UBEC that i bought new but didnt use from last year - its a decent quality unit which i would like to use - BUT it does not have an inbuilt volage display like the Align SBEC/UBEC thing does...

So im looking for some sort of add on to enable voltage readins - and maybe an alarm if it drops too low...

I have found this at BRC Hobbies

i'm thinking of using it in the 1S test mode - and connecting it in parallel with the UBEC - on the RX Lipo battery side...

This way it will give me a full voltage reading - and i think... provide an alarm if the pack drops too low..



What i'm wondering tho - does anyone have any suggestions or ideas on this issue..


Also - what do you reckon to the pack size that i've bought? I did a bit of googling before hand - and some people were fitting batteries upto 5000mah which seems WAY OTT!

I'm sure the old nimh RX packs were something like 1500mah?

Matt

[Richard]

Sounds like a good idea to me, neat device too.

I wonder if you really need it, do you fly all day or is about 4-5 flights at a time? I'd imagine the 2100mAh just driving the servos would last a lot longer than 5 flights.

I've seen 2400mAh Nicad packs 4 and 5 cells being used before lipos and regulators became the norm.

Anybody got some experience?

[YOUNG GUN]

(30-03-2011 21:01)Richard Wrote:  Anybody got some experience?

Thats what i'm looking for really...

When i did IC ages and ages ago - i just used the RX pack the radios come with - and it was fine for the few flights at a time i did...

But since converting to electric - i'v always just used the ESCs BEC OR in some cases - fitted a seperate UBEC to the main flight battery - just to take the load of the ESC OR to up the RX voltage to 6V for better servo performance.

In this case...

Its a larger heli - which is going to be using Govenor mode on the ESC and the ESC i've currently got is only 75amp... So i decided - for a SMOOTH & reliable power supply i'm going have to use a seperate LiPo + UBEC...

Which i have not done before...

And i know a lot of people use it - but i DONT like Align electronics... Just dont trust them at all. Hence why i would rather use this UBEC i've got going spare which i know is a decent one (having used one on a model previously for years)

I'm also not very keen on the idea of having a switch between the lipo and UBEC - i know its a slim chance - but what if it somehow gets knocked to the "OFF" postion while in flight... It looks like a failure point to me.


And Rich (so i havnt forgot you lol!):

In the past i'd take 2 or 3 models up to the field - and fly each one a couple of times - like you, each model having a different size battery...

Well.. all i will have now is this 1 model... and although there will be times where i only go up fly it a couple of times... I am also going to be flying it for half days or full days when i drive out to a field..

But the other side of it - I wouldn't feel like i could "Trust" the lipo having a charge in it - without actually checking its ok to go.. you know, it would be in the back of my mind for the whole flight... "Has it got enough charge in it or not"

So aside from it being another Gadget - its also a kind of saftey device - which for the £8 or whatever aint too bad.

Cheers
YG

[quorneng]

I suppose running the rx from the flight battery with some sort of LVC is a way of minimising the risk of loss of rx power although I appreciate its a bit different in a heli.
As far as I can see the only way to be absolutely sure of the charge state of an rx battery would be to change it at the same time as the flight pack. As it would only have to provide power for minutes rather than hours it could be quite a bit smaller.

However in the world of probability having two separate batteries to ensure flight does not necessarily mean improved reliability. Overall it would only be improved if the rx was protected by an automatic backup power supply.

This does raise the question of which part is most likely to fail. A dynamically loaded component is probably more at risk than a solid state one but predicting what and when something is going to fail is notoriously difficult.

Of course in the real world the human is considered the weakest component.

[Richard]

I can offer experience of another kind.

I charge my flight packs from the car battery. I use 6 cell 2500mAh packs on my Trex 500. Four recharges was all it did before needing jump leads to start the car The battery in the car was no more than a couple of years old... It wasn't a small battery either it had to swing a 1.9L diesel engine.

If you are charging from a car run the engine for 10-20mins after charging 3 packs and take jump leads

[giskard]

Honda make some nice generators too!

[YOUNG GUN]

hahaha that is very true - I am the weakest link in the whole setup...

But replacing me would take the fun out of it!


Being a Heli - using govenor mode - the flight battery & ESC is under enough demand as it is... Plus if something does fail (ESC highly possible) - then i need to be able divert the model down to the ground away from anything...

Of course --- you could go over the top - have 3 RX LiPos, 3 RXs - 3 TXs - all incase systems 1 - 2 fail...

But that wud be OTT for a model... fine for real aircraft.

I'm quite happy with the setup - just unsure about the on/off switch & if to have one at all.

I did think about having multiple smaller RX LiPos - but decided to go with the largest one i could fit in the space i had... We will have to see how many flights it will power... testing!

[YOUNG GUN]

(31-03-2011 18:08)Richard Wrote:  Four recharges was all it did before needing jump leads to start the car The battery in the car was no more than a couple of years old... It wasn't a small battery either it had to swing a 1.9L diesel engine.

I have thought about this too...

The LiPos i currently have can be charged at 5C - so i did think - if to just buy a field battery (of sorts) - and keep fast charging them while at the field.. meaning i would only need 2 - 4 lipos.

BUT when the lipos are 5000mah a piece.. it will soon drain a field battery.

Only real option is More LiPos and/or a generator or solar panel LOL. But then we run into that brick wall of CASH SHORTAGE!

Its a big problem with this hobby.. there is just no end to the stuff you can buy and the amounts you can spend.

They should pay me for testing the crashability of their products!

[quorneng]

A Honda generator to charge the batteries to fly a plane.

Now if you put an IC engine directly in the plane and use that to turn the prop.................! LOL