UBECs and lipo savers

[Yorkman]

Apologies if this has been covered elsewhere...when I 'converted' to lipos from nicads, I was advised I needed a 'lipo saver' which plugged in line with the ESC(s) (the model has two), which would reduce power to the motors well before the lipos approached their critical voltage (I presume this is well above the voltage of the normal bec motor shutdown)-all fitted, tested, performs as advertised.

However, as we know!, the accepted wisdom (especially with 2.4ghz) is to run a separate 6v UBEC for rx/servos, and disable the bec function of the esc, which I have now done....but which of course now renders the 'lipo saver' inoperable ...

Sooooo, is there a way round this? Or do I simply ensure my flight times are short enough to stay well clear of discharging the flight pack too far-which is my approach at the moment.

[Tim Mackey]

I would suggest your last paragraph is the correct approach.

Of course, if you use a dedicated Lipo compatible ESC (s ) then these will themselves have an LVC circuit designed to do the same thing.

I am afraid that yet AGAIN ( the 4th time in the last 2 days ) I must correct someone on the purpose of BEC and shutdowns etc.

Quote " (I presume this is well above the voltage of the normal bec motor shutdown)"

The BEC has nothing to do with shutting the motor off as the battery runs low - this is the sole job of the ESCs LVC gizmo. Incidentally, the ESC will shut down the motor WAY before the pack gets to the point where it can no longer feed the BEC to supply your radio...if it ever got that low - you have goosed your pack!

[winchweight]

I don't use lipo savers and have run down my lipos to the BEC/UBEC LVC without any problem.

I think the critical voltage is below the UBEC figures. I imagine it is more of an issue when using lipos in a non ESC / UBEC installation, e.g. as a rx battery in an i/c model.

[Yorkman]

Thanks guys-will carry on as I am, then....well, I will when we get some flying weather...

[Tim Mackey]

Shaun Chant wrote (see)

I don't use lipo savers and have run down my lipos to the BEC/UBEC LVC without any problem.

I think the critical voltage is below the UBEC figures. I imagine it is more of an issue when using lipos in a non ESC / UBEC installation, e.g. as a rx battery in an i/c model.

Are you trying to wind me up Mr Chant

THE BEC HAS NOTHING TO DO WITH THE LVC

ARRRRRGGGGGHHHHHH !!!!!!!!!

[Tim Mackey]

in case you missed it

[winchweight]

Sorry the esc LVC.....

I will not write without thinking

I will not write without thinking

I will not write without thinking

I will not write without thinking

I will not write without thinking

[Tim Mackey]

[Frank Skilbeck]

Yorkman, I guess you are running brushed motors off non Lipo ESC's hence the inclusion of a lipo saver to shut the motors down if the voltage drops too low.

I wouldn't worry about the UBEC carrying on powering the Rx with the small current involved I don't think you will be flying long enough once the power to the motors have been cut to cause any Lipo damage

Timbo - you got it the wrong way round THE LVC HAS NOTHING TO WITH THE BEC

[Myron Beaumont]

Steady now!

[Tim Mackey]

Frank Skilbeck wrote (see)

Yorkman, I guess you are running brushed motors off non Lipo ESC's hence the inclusion of a lipo saver to shut the motors down if the voltage drops too low.

I wouldn't worry about the UBEC carrying on powering the Rx with the small current involved I don't think you will be flying long enough once the power to the motors have been cut to cause any Lipo damage

Timbo - you got it the wrong way round THE LVC HAS NOTHING TO WITH THE BEC

And the difference is ?

[Frank Skilbeck]

Written one way round it's like the BEC has no effect on the LVC and the other way the LVC has no effect on the BEC.

Which is what you were trying to say, the LVC cuts power to the motor to save the Lipo but doesn't affect the BEC.

This is the reason why people damage their Lipo's when they forget to unplug them from the ESC, the BEC circuit is still live and will eventually drain the Lipo.

Also I thought it was worth repeating one more time

[Myron Beaumont]

Repeat what

[Frank Skilbeck]

THE LVC......................................................

[Yorkman]

Blimey guys, can we stop squabbling?

I understand the functions of both the BEC circuitry and the LVC circuitry, and perhaps am guilty of mixing my acronyms....,so will try again and hopefully not offend anyone this time!

Frank-you seem to have missed my point-yes, I am running brushed ESCs, which is why I was advised to use a Lipo saver...carefully now....which is in effect another LVC, (perhaps 'autothrottle' more accurately describes its function) upstream of the ESCs rx connection, linked to the balance lead of the lipo, so able to read the pack voltage and an appropriate shut off/voltage reduction point for that pack? At which time it reduces voltage to the ESCs to give a noticeable reduction in power as a physical indication. I've got that right?

However, having introduced a UBEC into the setup, I have disconnected the red power lead from the ESCs to the Rx (which had the lipo saver in series with it) which has rendered the lipo saver non-functioning, hence I am left with being careful as my way of preventing over-discharge..

That is my understanding of the situation-I stand ready to be corrected!

[Myron Beaumont]

If all these gissmos aren't related --Why are they all shrunk together with "genuine plastic" in a small heavy doo- dah you have to have with this 'lektrikkery as another way of adding weight to the aircraft  'cos they havn't got a proper engine .     I'll get mi coat ! 

[Yorkman]

Myron Beaumont wrote (see)

If all these gissmos aren't related --Why are they all shrunk together with "genuine plastic" in a small heavy doo- dah you have to have with this 'lektrikkery as another way of adding weight to the aircraft  'cos they havn't got a proper engine .     I'll get mi coat ! 

exactly!

[Myron Beaumont]

Thanks Yorkman  Thought I was on my own

[Yorkman]

do think it could do with a bit of standardisation and de-mystifying-too many options available, maybe?

i.c. flyer's model shop conversation-

'my model's this big'

'stick a 40 (60, whatever, as appropriate) in it'

'thanks'

[Myron Beaumont]

,xactly

[Frank Skilbeck]

True, but the guide of 80 plus watt per pound isn't a bad guide.

Sorry I misunderstood about the lipo saver I thought they plugged into the ESC - Rx Throttle connection and cut the throttle if the Lipo voltage went too low.

[Yorkman]

You are correct Frank, that's exactly what they do.

My 'problem' here, why I started this thread, is that using a UBEC renders the lipo saver inoperative, so an alternative method of lipo saving is needed.

'True, but the guide of 80 plus watt per pound isn't a bad guide.'

Which is fine, if you can work it out.....York is 6.5lbs, so 520 watts.....errr....

[Tim Mackey]

Myron Beaumont wrote (see)

If all these gissmos aren't related --Why are they all shrunk together with "genuine plastic" in a small heavy doo- dah you have to have with this 'lektrikkery as another way of adding weight to the aircraft  'cos they havn't got a proper engine .     I'll get mi coat ! 

Firstly guys no one is squabbling - my posts earlier "shouting" about the confusion between a BEC and an LVC, had ( as many of mine do ) a smiley / winky icon to illustrate that this, as with many posts is lighthearted - criticism / correction or whatever...but lighthearted. The purpose ( as I see it and please someone correct me if I am wrong ) of the forum, is to help, and educate people with any and all aspects of the sport.

The answer to the OP was given very early on, and Yorkman seemed satisfied with the information offered.

As for the later posts regarding the association of the BEC and the LVC ( or if, as some people seem to prefer the LVC and the BEC ) is not complicated at all as some less experienced flyers seem to suggest.

In the case of an ESC with built in BEC, yes, sure they are both on the same “gissmo” as Myron put it but they have no relationship with each other as far as operation is concerned.

"Standalone BECs" or UBECs as they are often called, have already been explained to Myron as he asked the question in another thread - they perform the exact same function as a BEC which may be built in to the ESC and their Circuit Eliminates the need for a seperate radio Battery, however they are usually better at the job than built in versions, and  so are preferred in many cases to the one which is built in to the ESC.

The LVC ( usually part of an ESC ) and the LVC alone is there to Cut off power to the motor only in the event that the main flight battery falls to a pre-set Low Voltage level - this can in some cases be done by a separate device (known as  a lipo saver) for situations ( as in Yorkmans ) where the ESC has no suitable LVC for the type of battery deployed. The further advantage of these Lipo savers is that they usually connect to the battery alance port plug, and monitor not just the overall voltage of the battery, but also the stae of each individual cell, cutting / slowing / pulsing tghe motor if ANY indidvidual cell gets too low. These are great devices, and can sometimes be found in some ESCs rather than having to be purchased separately. Power is continued to be supplied to the radio gear for "ages" after the LVC kicks in, and in fact would need to be dropped to a critically stupid low level before the BEC ceased to supply power to the radio. As stated, leaving the battery connected will eventually drain the battery - probably ruining it  - which is why it is important to get in the routine of disconnecting your flight pack IMMEDIATELY you land.

[Tim Mackey]

The guide of 80 watts per pound - as with ANY guide - is exactly that; If your model weighs 6.5lbs, and 80WPlb is your target - ( and it may well NOT be depending on the model ) then simply round things off a little..... a la

6.5 x 80 = 520 .............so get a 500 or 600 watt setup.

Simple really

[Yorkman]

hi Timbo-my 'squabbling' comment should have had a smiley appended to it, sorry! Not taking any of this too seriously (except the info of course!)-as far as I'm concerned, it's all light-hearted, unless someone makes it very clear it isn't!

As for the watts calculation-no problem with that, just with having any idea how many I've actually got....

Ah well-the York hauls itself off the ground and trundles around the sky on half throttle, so I guess whatever I do have is 'adequate' as Rolls-Royce used to say!