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> 7.2V Receivers

PostPosted: Thu May 13, 2010 12:37 pm
by GeicoGecko
Any idea if receivers will become tolerant of being connected to 2s lipos?

Are there any disadvantages to using lipos as an RX pack?

Re: > 7.2V Receivers

PostPosted: Thu May 13, 2010 6:36 pm
by hakank
Spektrum receivers manage 9v. In some applications I use 2 life acc's. What I like is them always ready to fly if charged after last flight. They are also able to deliver a lot of power which can be useful in the event of current consuming servos.


Re: > 7.2V Receivers

PostPosted: Thu May 13, 2010 8:06 pm
by GeicoGecko
I suppose I didn't really consider the problem. Whilst the receivers will take the voltage it's the servos that need to support it as well. I'm always wary of using a voltage regulator as it's something else to go wrong.

I generally use Hitec servos and they are only spec'd to 6V. They say you can use higher voltages but this will vastly reduce the life of the servo.

In two minds what to do... suppose the safest option is to stick with NiMh...

Re: > 7.2V Receivers

PostPosted: Thu May 13, 2010 9:27 pm
by RCModelReviews
My receiver pack of choice is LiFePO4 (A123).

These packs put out 6.6V which is low enough to avoid damaging receivers or (most) servos and the A123 cells have a more than 30C rating, which means you aren't going to get brownouts, no matter what the load.

For more info on the various battery technologies I suggest you read this article on the RCModelReviews website.

As for receivers, I know that FrSky are producing an "HV" version of their receivers that will safely run directly from a 2S LiPo and there are also a number of HV servos available from various manufacturers that will also run on 2S LiPo.

However, as I see it, LiPo has too many downsides for use in a receiver/servo pack.

For instance, have you ever left a model accidentally turned on when you put it away and come back to find the batteries were dead flat?

If you were using a LiPo then that battery would be wrecked.

If you were using a LiFePO4/A123 pack then you could just recharge and fly again (I know this because I've left the same model turned on several times and totally flattened the A123 pack in it -- it still has full capacity even after this abuse).

Re: > 7.2V Receivers

PostPosted: Thu May 13, 2010 9:44 pm
by GeicoGecko
That all makes sense and I now understand the benefit. What's te reason for most hobby places not stocking the LiFePO4 batteries already made up? Is it because the technology is too new and takes a while to adopt?

You mention being able to make packs for $10 a shot, admitedly I've yet to look but can you recommend sources for batteries? Do these have soldier tabs already welded on?


Re: > 7.2V Receivers

PostPosted: Thu May 13, 2010 10:58 pm
by RCModelReviews
The $8/$10 packs as I used in the FlySky/iMax/Turnigy conversion are lithium ion batteries which have the same output voltage as LiPo so they're not suitable for receiver packs.

You can get genuine 1100mAH A123 cells from HobbyKing for about $13 (less if you're a platinum member) and they come with solder tags that make assembling your own receiver packs very easy.

Just grab an old servo extension and you can use that for the battery connector as well.

Re: > 7.2V Receivers

PostPosted: Thu Jul 29, 2010 12:46 am
by Mr Ed
I just read on one of the forums that the Airtronics FHSS 3 receiver is good to go with a 2 cell LiPo now. They had been testing it for about a year now and haven't had any problems with the receiver having a shorter live span. The bad part is, the servos for running that kind of voltage are rather limited. I know JR has a couple, but they are expensive one too. Not much call for high voltage servos, except for maybe the high torque high end servos. Most servos are limited to 6 volts with some at 4.8 volts.


Re: > 7.2V Receivers

PostPosted: Thu Jul 29, 2010 1:21 am
by RCModelReviews
I still don't see the point in using a 2S lipo for your receiver/servo pack when LiFePO4/A123 offers a vastly superior alternative.

Re: > 7.2V Receivers

PostPosted: Thu Jul 29, 2010 8:14 am
by GeicoGecko
I think it's the availibility and newness of A123. Given time I'm sure they'll catch on :)

Re: > 7.2V Receivers

PostPosted: Thu Jul 29, 2010 8:53 am
by RCModelReviews
A123s have been around for a couple of years -- that's how long I've been using them.

They're well-tested and most of the Giant-scale and turbine guys are now using them.

DeWalt have well and truly tested them in their cordless tools too ;-)