gunneredwards

My Feedback: (4)

Can anyone tell me why the radio system comes with no receiver battery pack? I have the stock charger and am trying to figure out what the charge time will be for a 2700mah 4.8v pack. I was reading the radio manual and it stated the servos will not operate below 3.5 volts, is this normal? The servos are the same that i have been using in my other planes with 72mhz and the stock 4.8v 650mah futaba batteries, why would this change or was i just ignorant to the power they use?
dan

opjose

I don't know which radio you purchased...

Most TX's come with fairly low capacity battery packs. I typically toss these and purchase something with higher capacity.
As such I don't see any loss to the removal of the battery packs, especially if it saves me a few dollars on the TX.

As far as charge time, take the capacity of the battery and divide it by the output amperage of the charger.
Nothing to it.

So if you are using a 50mA charger it will take 54 hours to charge your pack from a completely discharged state.

Note however that you may not be able to charge a pack to the full rated capacity, nor discharge it completely so actual charge times can be less than this. Also inefficiencies come into play as well.

There are plenty of "charge time calculators" on-line ( hint: google ).

Re: Power

By the time your packs hit 3.5v it is pretty much discharged completely.
The electronics will not receive sufficient operating current when the packs are down to this level.

Most servos can use up to 1 to 2 AMPS(!!!) each when fully stalled... so those 650mAh batteries are practically a joke.

In actual operation we tend to use less than that.

I saw an article for beginners today that recommended this battery pack formula as a STARTING point...

Battery Pack capacity needed on plane = 1000mAh + ( 250mA * Number of Servos used in Plane ).

That is more realistic.

goirish

that makes lots of sense to me. Had not seen that formula before. I normally use 2500mAh in both tx and rx. The only 4.8v I use is for the ignition on my gasser. It is also a 2500mAh

gunneredwards

My Feedback: (4)

I got a Spektrum dx7 and ar7000 receiver. the tx is all stock and I have no idea what battery choice to get for the receiver. I have heard of the brownout problem, but why do the spektrum/2.4ghz need so much more power?
dan

tacx

My Feedback: (1)

If you purchased a DX7 package, you should have gotten a Rx battery with it.

CGRetired

My Feedback: (1)

First of all, power isn't the point, it's the capacity, which in the case of the example, 2700 mah is the capacity, not the power. Power is usually expressed as watts. Anyway, most people put higher capacity packs to get more life or more flights per flying day out of the pack.

The so-called "brownout" you are talking about was a problem that was mainly caused by operating the receivers with battery packs that were running low. The voltage threshold for the receiver was fairly high, but lower than normal operating voltages most of us used. Spektrum changed the "time to reboot" the receiver so that if it did go into a cycle, it would take less time for it to recover. Most of us overcame that by using 6 volt packs so that the battery voltage never drops low enough to cause the "brownout".

CGr.

MetallicaJunkie

i used to use 4.8 on my ignitions, not anymore....i now use a 6 volt 2500 mah AA pack with a cheap inline 6.0 v reg on the output of the switch... with a 4.8 pack, if you lose a cell, your motor will die

BarracudaHockey

My Feedback: (11)

Running a 5 cell pack gives you some wiggle room if you're not vigilant on checking your packs or if a cell fails.

opjose

Be careful with a 6v regulator on a 6v pack...

Normally the regulators step the voltage down by dissipating excess current as heat or via switching to capacitors, etc.

I had a friend who did exactly what you are doing, and we spent about a half hour setting his control horn throws, up at the field.

The relatively small amount of actual on time was more than enough to deplete the batteries because of the drain of the regulator.

His plane started glitching as we were getting ready for it's first flight... due to insufficient battery power...


I had him switch to higher voltage, but same capacity packs and this made all the difference with his regulator.

He's getting a good six times the initial 12-15 minutes of on time he had before.

nate691023

IF you go to Spektrum web Site. It say that it ca handle 3.8v - 9v..
On the RX.. So can i use a 7.4 15 c lipo in the RC Plane?

landeck

My Feedback: (1)

The problem is not the receiver but the servos. The large majority of servos will only handle up to a nominal 6 volts. There are some new high voltage servos but the tend to be expensive. If you want to use something other than NiCad/NiMh batteries you might look into using two A123 cell battery packs or get a 6 volt regulator to step down the voltage for a LiPo pack.

Bruce

CGRetired

My Feedback: (1)

There is one exception and that is the new LiFe packs... Lithium Iron Phosphate packs, which have a nominal voltage of 3.3 per cell. The packs are 2 cells which means nominal 6.6 volts per cell and are stated to be able to be used as direct replacement for 5 cell LiPo or NiMh packs. They are lighter and have a sufficient C rating to be used to power receivers and servos.

One caution, though, they require a specific type of charger.

Check them out at Tower Hobbies at the following link:

http://www3.towerhobbies.com/cgi-bin...&I=LXYAS8&P=ML

These are 1800 mah two cell packs.

CGr.