preparation_h

I bought a used computer radio JRxp87something, that drains batteries within 20-30 minutes. I believe I have a 700mah battery in it. Is there a possiblity to swap over to a higher rated 1400 mah NImh, or do I need to upgrade to a better Nicd Battery Which is the original type of battery that came in the unit?

Much Thanks!

Rodney

How have you been charging that battery? If you have been using the wall wart (slow overnight charge) then your battery is probably due for replacement. If you have been fast charging, try a slow overnight charge (16 hours at 0.1C) and see if the battery does not provide a longer run time.

preparation_h

Brand new battery, 700 Mah Sanyo, does the same thing as the original. Seems to lose a charge even if I don't turn on the transmitter.

OldScaleGuy

My Feedback: (2)

You can change it over to the higher mah NiMH without any problems. I do all my JR's tx's with that change.

Nathan King

You could do this, but IMHO that is just covering up the problem which will eventually come back to haunt you. Most transmitters draw around 600 - 700mA of current (Spektrum draws considerably less). This means that your transmitter should last around an hour. Your transmitter is drawing somewhere around 1.4 Amps of current, which is high. I would send it in to be checked out.

FYI: Most of us use batteries rated from 1300 - 2200 mAh. 700mAh is a bit small for my liking.

JohnBuckner

My Feedback: (1)

Nicd and Nimh do self discharge so how long a period between any charging and use are you doing?

How many hours did you charge this new battery the first time?

Were you using a wall charger and was the little light on while it was plugged in?

Mode One

The best advice you have gotten so far is to send the unit in for service. R/C sets are set-up to provide around 1.5 hours of continuous use before needing re-charging. Yours is not making this standard and the reason why needs to be determined.

telejojo

I bought a 2100 mp lipo for mine and have used it for 5 days at the field and it's still at 11.2 volts.........

preparation_h

Can I charge the NImh batteries with the same wall charger that came with the transmitter?

Mode One

Yes

Tired Old Man

My Feedback: (1)

JR has nimh replacement batteries for their transmitters. Their original 9303 comes with a 600 or 700 mAh battery and runs down very quickly. Three of four flights with the standard battery and it's getting mighty close to needing a charge. Computer radios with multiple functions and memories use more current.

JR suggests using a slightly different wall charger with the 2,500 mAh nimh transmitter battery they sell, and may have a similar suggestion with their other transmitters. You can send the radio in for service but I'm pretty certain it will come back as having been fine when it arrived at their shop. The transmitter batteries installed at the factory are minimum sized for anyone that plans on more than three or flights between charges. Good marketing strategy for later sales, get the end user to upgrade to better batteries some time after the initial purchase because the transmitter drops voltage so quickly due to a poorly sized OEM battery...

Mode One

If the manufacturers are supplying minimal TX battery packs that allows only 45-60 minutes of discharge before needing recharge, the manufacturer is not providing the kind of services/products which the public should expect! I have an Airtronics VG6000 computer radio and am not seeing this short of a discharge cycle.

Of course if you are going to install a larger MAh pack, you will want to be able to charge at a higher rate. In this case you should consider a higher capacity charger. However, Prep. H has only mentioned similar packs to what he has. Therefore his wall charger would handle NiCad or NiMH cells, which I took to be his question.

Tired Old Man

My Feedback: (1)

The standard wall wart charger will charge the battery...mostly...but not completely due to the low input levels. That's been covered many times before when large capacity nicads first started getting used. The radio wall chargers would get them to partial capacity, but rarely to full capacity even if left charging for several days. So the first thing that happens is a new battery develops a memory of having been fully charged when it was only partially charged. Most slow charge rates for a nimh or nicad should be around 1/10 C, or 250 mAh/hour for a 2,500 mAh battery. A 1,500 mAh battery would require a charge rate of 150mAh/hour. Most wall warts charge at a rate of around 50 mAh/hour.

I won't even try to debate manufacturers shorting the customers by undersizing components in order to increase sales by to customers "upgrading" to correctly sized components. Several manufacturers do this, and have been doing it for years. Why do you think a certain radio manufacturer came out with an optional two battery receiver system for their 2.4 gig radios? They found out the hard way (poor product testing practices?) that a single battery gets eaten up pretty quickly and it's much more profitable for them to sell as an option what should have been there in the first place.

Another manufacturer/distributor grossly undersizes the sizes of electric motors and batteries that should be used in their planes. When they fly poorly, or not at all, the customers line up to order what should have been there to begin with. It's not right but they've been getting away with it for so long that people have become conditioned to accept it.

Rodney

I see the comment that you can not fully charge the bigger capacity batteries with the standard wall wart. This is not true, it is true that it will take longer but; as long as the voltage of the charger is adequate (regardless of its current capacity) it will fully charge the battery as long as the charge current exceeds the self discharge current--a simple fact of physics.

Tired Old Man

My Feedback: (1)

And there lies the problem. What is the known self discharge rate for any given group of batteries. That has a large effect on the required charge time with a 50 mAh input.

AA5BY

The capacity of a nicad battery may have fallen significantly from its posted rating due to age or memory. A battery cycler is a must when using nicads. After a dozen or so cycles, the battery should be fully charged at c10 rate for 16 hrs and then discharged to check for capacity.

If it falls below 80 percent of battery rating it should be cycled by charging and discharging using a cycler and if it does not rise above 75 percent rating, replace it.

Nicads lose 10 percent of their charge a week when left idle. NiMH seem to lose more as well as are very poor in their output at low temperatures.

I'd suggest investing in a cycler. Choose a reasonably good one that will handle both transmit and receive at the same time and one that has a choice of charge rates at least up to 140 ma for the larger capacity packs. SR Batteries claims that if charging less than C10, the batteries will not reach full capacity and for this reason many of the cyclers charge at c10 and then go into float mode so that they can be charged at C10 and then go into float mode after 16 hrs or when the condition of the battery is believed by the charger to be fully charged.

This is contrary to the belief that a low output wall charger will get there eventually. Not all nicads have the same impedance or internal resistance so a charge voltage overhead may need to be different for a given battery pack. A wall charger that will charge a low impedance pack may fail to adequately charge a higher impedance pack.