LiPo Tx Battery Packs

[djmcnz 754]

So I've decided to finally move to a rechargeable battery pack for my Tx and am dumping the single cells, I have a few questions, any insight?

1. My Tx has an accurate battery voltage display and a low battery warning but these can't be configured or set. I assume the low battery warning will not be calibrated for LiPo and I should not depend on that - good assumption?

2. Assuming I can't rely on the warning, I can leave the Tx display on charge level when I'm running (I don't need to view the other screens whilst running) but what level is "low" for a 11.1v 3s?

3. Even though the packs are cheap I'd prefer an alarm - can I fit an inline LV alarm/cutoff between the Tx and battery pack? The Rx has steering and throttle fail safes so if the Tx cuts the vehicle will roll to a stop in a straight line.

4. What would happen if somebody plugged a charger into the charging port on my Tx if the LiPo pack was plugged in? Should I snip the wires as a precaution?

5. Am I being paranoid...

6. I see 1450mah all the way up to 3600mah... really I'll probably charge the Tx pack each time I charge my race packs, how long could I expect a fully charged 1450mah pack to last (my Tx manual only calls for a 700mah pack)?

7. Should I be asking any other dumb or intelligent questions?

Tks.

[TA-Mark 195]

Low voltage for a 11.1v Li-Po is the same as for for any other Li-Po, 3.0v per cell, so 9.0v for 3 cells. Good to use a small overhead so that one of the cells doesn't drop below 3.0v if the pack becomes unbalanced. I would shut them off at the 9.4v/9.5v area.

As you know Li-Pos really should be balanced charged, so even if the right type of charger was plugged into the TX charge socket it wouldn't be a balance charge, so best to unsolder and insulate one of the wires from the charge input terminals. Plugging a Ni-MH/Ni-Cd type charger into the socket could be disastrous with a Li-Po in the battery holder.

I get several hours of use with 2500mAh Ni-MH AA cells. You'd have to expect similar 'up' times with similar capacity Li-Pos. Low voltage alarm for 3S might be a good idea as the current draw from a TX is not high, unless the LED backlight is lit, and even then it's not great. The low voltage could creep up on you if you don't check the voltage display on the screen often. An audible alarm should be sufficient as the transmitter is in you hands and never any sort of distance away.

A fully charged 3S Li-Po is 12.6v. The TX should be fine with this slightly higher voltage. Check the spec sheet to confirm it before plugging it in.

[richard.tufty 20]

I use 9.9v Gens Ace LiFe packs in 2 of my transmitters, they were dirt cheap from Hobbypartz.com (in the US) at just over $10 each. There is no low voltage cutoff needed for LiFe, so no need for any monitoring or cutoffs. The packs I have fit in transmitters which normally have 8 AAs side by side thusly:

IIIIIIII

but not in the ones where they are arranged like this:

--

--

--

--

Apologies for my poor ASCII art!

Link: http://www.hobbypartz.com/98p-life-1c-1500-3s1p-aaa.html

[GregM 1109]

Those transmitter LiPo batteries sound interesting. At the moment, I'm using Eneloop NiMH batteries in all my transmitters, as they do not selfdischarge as fast as regular NiMHs, when not in use.

[alfagta 126]

some good advice above , i have yet to swap from ni-mh as i get over 12 hours of use from a single charge to the 4 AA that my aging DX3R uses , if i went to li-po it would save a few gram's but it simply wouldn't be of any real benefit , i can see the appeal for all you guys that use 8 cells , if i was you i would be looking at the li-fe packs as they should be perfect for the application , with a little careful modification i am sure you could build a balance port into the transmitter for easy safe charging too and remove the old charging port completely to save any possible 'wrong charger issues' ,

[TA-Mark 195]

with a little careful modification i am sure you could build a balance port into the transmitter for easy safe charging too

Safe is remove the Li-Po pack from the TX and charge it in a Li-Po sack or fire safe container. I wouldn't risk my TX (Futaba 3PKSs) to charge with even Ni-MH/Ni-Cd in it just as I wouldn't charge with a pack in a car. 3PKS is worth more than some of the models it controls.

[alfagta 126]

Safe is remove the Li-Po pack from the TX and charge it in a Li-Po sack or fire safe container. I wouldn't risk my TX (Futaba 3PKSs) to charge with even Ni-MH/Ni-Cd in it just as I wouldn't charge with a pack in a car. 3PKS is worth more than some of the models it controls.

nothing wrong with the belt and braces approach ,

although i cant foresee an issue with charging in the transmitter as long as the charge current is kept to1C or even 0.5 or 0.25 C with li-fe packs to keep any chance of heat low , even lipo , after all i charge a £400 mobile phone at 1C every few days with an even more risky li-ion cell in it and my lap top for that matter , the simple truth about lithium technology is that it is extremely safe as long as the user abides by a few simple rules , but hey its your kit and i can fully understand your trepidation .

[djmcnz 754]

Thanks for all the great information guys, very helpful.

I also found this really useful post: http://www.rcgroups....85&postcount=54

Low voltage for a 11.1v Li-Po is the same as for for any other Li-Po, 3.0v per cell, so 9.0v for 3 cells. Good to use a small overhead so that one of the cells doesn't drop below 3.0v if the pack becomes unbalanced. I would shut them off at the 9.4v/9.5v area.

As you know Li-Pos really should be balanced charged, so even if the right type of charger was plugged into the TX charge socket it wouldn't be a balance charge, so best to unsolder and insulate one of the wires from the charge input terminals. Plugging a Ni-MH/Ni-Cd type charger into the socket could be disastrous with a Li-Po in the battery holder.

I get several hours of use with 2500mAh Ni-MH AA cells. You'd have to expect similar 'up' times with similar capacity Li-Pos. Low voltage alarm for 3S might be a good idea as the current draw from a TX is not high, unless the LED backlight is lit, and even then it's not great. The low voltage could creep up on you if you don't check the voltage display on the screen often. An audible alarm should be sufficient as the transmitter is in you hands and never any sort of distance away.

A fully charged 3S Li-Po is 12.6v. The TX should be fine with this slightly higher voltage. Check the spec sheet to confirm it before plugging it in.

Good point on the display Mark and after looking I see that a LVA is only a few bucks so well worth the investment. It may fit in the battery bay as well but if not I think I'll be able to tuck it into the pistol grip which is mostly hollow.

Hopefully I won't blow the radio! There's no particular warning and there are some general reports of success on the web with the 12.6v initial charge of a 3S. The information in the link I posted above, which seems credible, suggests I'll be fine (I use alkaline batteries now). I could always set the max charge to 12.3v I suppose.

I'll disconnect the charger port, there are a few horror stories out there about that! And the battery will be balance charged with my proper charger.

I use 9.9v Gens Ace LiFe packs in 2 of my transmitters, they were dirt cheap from Hobbypartz.com (in the US) at just over $10 each. There is no low voltage cutoff needed for LiFe, so no need for any monitoring or cutoffs. The packs I have fit in transmitters which normally have 8 AAs side by side thusly:

Apologies for my poor ASCII art!

Link: http://www.hobbypart...0-3s1p-aaa.html

Love the art, know exactly what you mean! I do have the alternative battery configuration but your post made me look at LiFe batteries too, thank you.

There are flat LiFe packs I could use in my Tx but the jury is out on whether they're better. The prevailing opinion is that if you know how to treat LiPo's safely they're probably a better deal. The initial charge (9.9v) and flat discharge curve of LiFe can apparently be troublesome... more trouble with a plane and no fail-safe but probably not ideal.

Those transmitter LiPo batteries sound interesting. At the moment, I'm using Eneloop NiMH batteries in all my transmitters, as they do not selfdischarge as fast as regular NiMHs, when not in use.

I wasn't aware of the Eneloop's myself and people rave about them now that I look. I'm turned off by the charging time... it will take hours to charge 8 cells, even with 2 quick chargers! And I'd have to buy the charger(s) whereas I already have a suitable LiPo/LiFe charger.

nothing wrong with the belt and braces approach ,

although i cant foresee an issue with charging in the transmitter as long as the charge current is kept to1C or even 0.5 or 0.25 C with li-fe packs to keep any chance of heat low , even lipo , after all i charge a £400 mobile phone at 1C every few days with an even more risky li-ion cell in it and my lap top for that matter , the simple truth about lithium technology is that it is extremely safe as long as the user abides by a few simple rules , but hey its your kit and i can fully understand your trepidation .

My initial reaction to this was "no", I want my batteries out in the open and visible when I charge them. But it's a neat idea so I thought about it some more and I'd say, if I could also integrate the temp sensor from my charger into the Tx then it might become plausible because it does do auto shut-off. But I think once you're getting to that level of sophistication you might just as well remove the battery to charge it...

For piece of mind I never charge my batteries in my vehicles, I'll apply the same caution here, however unnecessary it might be.