Lipo 4S battery in an XMAG

[livebrando]

To anyone who's also into RCs, is it possible to put a 4S lipo battery on an xmag? It's only 14.8v, wondering if it's enough juice.

[knownothingmags]

To anyone who's also into RCs, is it possible to put a 4S lipo battery on an xmag? It's only 14.8v, wondering if it's enough juice.
yes and no,

there are alot of specs that need to be considered when it comes to the lipo.


i think you need to go up to 5s.

not sure though.

no one that i know has come up with a good lipo setup for runing your x-mag off of.

trial and error.

you need the voltage specs of the board also.

let us know if you find something out.

im working on my own lipo setup right now.

[sQuidvision]

you will need a voltage cutoff so you dont drain your pack too low... other than that i dont see why you wouldnt be able to use a LiPo... Keep us posted with what you come up with!

[GEE TEE]

I've just bought 50 x 1.2V 900mah NiMh flat top batteries. Going to have a go at making my own rechargable Emag and 'bone' style Halo packs. Don't suppose anyone has a spare clip or two from a shot AGD battery pack they want to sell to me?

[athomas]

Here is a copy of a battery pack explanation I did a while back.

14.8V would cause a reduction in power by about 22%. That should still trip the sear, but it would cut into any buffer needed to maintain operational consistency in all instances. That means you better keep the mechanism clean. It would probably be better to add an extra cell.

Don't go exactly by the rating on the cells or packs. In reality, Lipo cells have a fully charged voltage value of 4.25V so most charger limit it to 4.2V. The minimum safe voltage is 3V so most use a cutoff of 3.3V. That gives a four cell pack a voltage range of 13.2V to 16.8V. The discharge line from 16.8V to 13.2V is fairly linear and results in the 14.8V nominal rating. The calculations show a 15V average but in reality its not perfectly linear so the real average is 14.8V.

NiMh cells have a fully charged voltage value of about 1.4V but it drops to 1.3V very quickly so the 1.3V value is used for the upper value when determining average operating outputs. The minimum voltage is 1.0V, but the drop from 1.1V to 1.0V occurs very quickly so the 1.1V value is used for the lower voltage. The resulting average is 1.2V which is the industry value used for packaging. A 14 cell pack rated at 16.8v actually ranges from 18.2V to 15.4V.

Checking the voltage values of the lowest value for each pack type, it shows a reduction in power by 27% compared to the NiMh pack. This is worst than the 22% calculated using nominal values. As the pack gets discharged, you might end up with firing issues using a 14.8V LiPo pack.

[RST]

Thank you for the detailed explanation! :hail:

[hitech]

But would't the 5 cell work? I remember measuring the open circuit voltage of my eMag battery at somewhere near 20 volts after being fully charged...

[rukh013]

i'm going to try this as well

google this (http://www.google.com/search?q=low+voltage+cutoff+for+lipo&hl=en&biw=1366&bih=681&prmd=imvns&source=univ&tbm=shop&tbo=u&sa=X&ei=x7qAUNE-h8LZBdXegJAL&sqi=2&ved=0CDkQsxg) for the low voltage issue

[bss]

Lipo batteries are great for my RC helicopter. Lots of power and longer run time. Couple of things you should know. Lipo batteries require a special Lipo battery charger. The charging time for a Lipo battery is a few hours. If you over charge your battery, it will go into flames. Goto link to watch the video clip. http://www.youtube.com/watch?v=ixIOEPnsgbI&feature=fvwrel

[rukh013]

What about LiFe Poly batteries, a little more expensive unless you buy in bulk

But a regular emag battery is $60 anyway

[knownothingmags]

What about LiFe Poly batteries, a little more expensive unless you buy in bulk

But a regular emag battery is $60 anyway
LiFe are ok but still a joke compared to the lipo you can get your hands on now adays.

i have some pull with an rc company here in Cali. is there enough interest to get a custom pack made?

[rukh013]

LiFe are ok but still a joke compared to the lipo you can get your hands on now adays.

i have some pull with an rc company here in Cali. is there enough interest to get a custom pack made?


Three please :D

[rukh013]

Would it be easier to modify the wires to the board so they work with the battery pack (adding a ground wire, instead off thru the frame would help)

[athomas]

But would't the 5 cell work? I remember measuring the open circuit voltage of my eMag battery at somewhere near 20 volts after being fully charged...Yes. I would recommend the 5 cell LiPo as well. The 20V NiMh measurement usually settles to about 18V after a bit. If not, then it does as soon as you start drawing current off the pack.


The overall voltage will be a bit higher using the 5 cell LiPo pack. This will cause higher current draw which will heat the solenoid more. Its a 20% increase in power consumption when the battery is fully charged. I don't think the dwell of the solenoid will allow it to catastrophically overheat. If it proves to be a problem, put a 5Watt 0.5ohm resistor in series with the battery pack. That will bring the pack down to the same operating parameters as a NiMh pack.

[PsychoMag]

I stopped running electric rc cars about 10 years ago. What type of charger will it use? And what will the overall cost be for a pack and charger?

[sQuidvision]

As always, depending on cost I would be down for one.

[hitech]

I take it nimh batteries have the surface charge phenomenon like lead acid natteries.batteries. the resistor woild be a good and easy addition.

[athomas]

Yeah, I guess you could call it surface charge. Its about 0.1V above the stable high voltage value for each cell. For NiMh cells the stable charged value is about 1.3V. A 14cell NiMh pack like the emag pack would result in max charge of 1.4V x 14 = 19.6V, which is close to the 20V that most experience on a newly charged pack. After is sits, it settles to 1.3V x 14 = 18.2V. If the pack is really good and has almost no leakage, it might stay close to 19.6V until it starts delivering current to a load.


For charging, each cell must be done individually. That is why you see special multi-pin connectors on LiPo packs. I have seen LiPo mult-cell chargers for as low as $30 and 5s battery packs as low as $50.