flybyjohn

My Feedback: (2)

I recently had an glow airplane go down because of a low battery or a battery that could not discharge fast enough to maintain control. So I built two load jumpers to check the battery. One used a flashlight bulb, (6v,k13,kpr113) which says 4.8V - 0.75A - 3.6w. This one allowed one pack to sit around and slowly drain but the pack was holding around 4.45V but it was also not fully charged. The second pack that was in the airplane that crashed went from 5v and dropped instantly down to 1.2V and the bulb would go off.

The second load jumper I made was (2)- 10ohm, 1 watt resisters soldered in series (gave total resistance of 20.3 ohms) and when testing the second battery pack held near 5volts.

So my questions are: does the bulb jumper just draw current quicker than the pack can discharge it, and how do you tell how much draw your plane system has on it to be able to make a jumper that would simulate the plane system so I can make the correct jumper to accurately check the battery? Can I hook the volt meter on the plane and put some resistance on the control surfaces and then check the voltage, then choose resisters that match the same voltage when hooked to the same battery?

Clear as mud?

Any comments or answers are always welcome.

Thanks,
John

AWorrest

My Feedback: (5)

What you need is an ammeter. It can be a part of a multi meter such as the ones sold by Harbor Freight for a couple of dollars or something more expensive that is designed for electric models.

What I find interesting is that the pack that caused your crash should act so differently with a 750 mA load on the light bulbs and the 250 mA load with the resistors. Now light bulbs are good testing devices for batteries as the current load stays more constant than it will with a resistor load. I can think of three reasons for the discrepancy. First the pack was near discharge when you tested it with the bulb and charged when tested with the resistor. Second either the bulb is drawing much more than 750 mA or the resistor load is drawing much less than 250 mA. Or third, that pack has one heck of internal resistance. Probably the cause is something else. Good luck.

Allan

airbusdrvr

I and a several people at my field use these, http://www3.towerhobbies.com/cgi-bin...&I=LXEYM6&P=ML . In fact, I check my plane battery before every flight. The test load is adjustable, depending on your type airplane.

AWorrest

My Feedback: (5)

John,

The amperage you draw will depend on your system. I have read of recommendation of using 300-500 mA to measure the capacity of receiver batteries. I have a Hangar 9 loaded voltmeter that has .5, 1, and 2 amp loads. For the average airplane your bulb, if it is labeled correctly, is closer to being realistic than the resistors.

Allan

BuschBarber

My Feedback: (2)

I use the H9 Voltmeter. I use .5a for Nicad/NiMh and 1a for Lituiums. You can plug it in to the Charging Jack, on the Switch Harness, or plug it directly into the battery. You definately need to put a load on your voltage readings in order to determine the status of the battery. It is a good idea to leave it on for 30 sec and make sure the voltage reading stays steady and does not drop suddenly. You can put a 5 min charge on a fully discharged 4.8v battery and still get a 5v reading for a few seconds.