Making a load meter
 

I have read that you can make your own load meter.( providing you have a meter) to check rx batteries,by putting resistors in series with the battery and meter. Sounds good as a few resistors are a lot cheaper then a load meter. Can anyone tell me what size resistors to use to check a 4.8 volt battery pack? I have standard servos that came with my hanger 9 Alpha 40.

RE: Making a load meter
 

I forget the value of the resistors but they are installed in parallel to the battery AND meter. http://www.geistware.com/rcmodeling/...ronto.htm#ldva

RE: Making a load meter
 

A 16 ohm resistor would do fine (Brown, Blue, Black, Gold). This will put about a 300mA load on your receiver battery. You can figure out different sized resistors for different loads using Ohm's law. V=IR (Voltage = Current * Resistance). Simple Middle School algebra will yield R = V/I. Plug in receiver voltage for V and your desired load for I (in milli-amps, ex. .3 for 300mA). Your answer will be in ohms.

RE: Making a load meter
 

Forgot to mention that you need to get a 16 ohm resistor with at least a certian watt value. P = IV (P is power, in watts). Therefore, a fully charged 4.8V battery with that 16 ohm resistor will draw ~1.59 watts. Therefore you should get at least a two watt resistor.

RE: Making a load meter
 

And the more "precise" the resistor the more accurate your readings will be.

RE: Making a load meter
 

Yes, the gold stripe on the resistor indicates a tolerance of +/- 5%. Silver indicates +/- 10%. There are other tolerances, but those are the most common. Try to get a gold fourth band.

RE: Making a load meter
 

Actually, I prefer 1% wire-wound (or similar) power resistors. Don't know if Radio Shack carries them though.

RE: Making a load meter
 

Thanks to all for your expert advice. I knew in ohms law you need at least two knowns, to get a third. I only knew one (volts 4.8)

RE: Making a load meter
 

Those are really good if you can find them locally and don't have to order them.

RE: Making a load meter
 

Or, for about the same money, you can get a VoltWatch and get an accurate reading from the load your electronics put on the battery. And it won't burn your finger when you touch it.:)

For bench testing a battery, I use 15ohm 10W wirewound for testing. It gets hot. I use this for a load on a pack so I can test individual cell voltage.

For day to day use though, A voltwatch or a comerical loaded expanded scale volt meter are two inexpensive and accurate ways to check your battery. The first does it all the time and the later when you remember. As you should do a check prior to every flight, digging out resistors and leads and meter to check you battery at the field would be a real. A volt watch is about $10 and Tower expaneded scale is $8.00 http://www3.towerhobbies.com/cgi-bin...?&I=LXNK82&P=7 Cant get much cheaper and if your meter blows off the bench, or you step on it, you haven't lost much.

Don

RE: Making a load meter
 

you can buy what you need cheaper than you can make one and the store bought one will be less likely to short out

RE: Making a load meter
 

The simplest solution is to buy a flashlight bulb, e.g., 6V/2.4W (or something similar) and use that for a load. It has the added advantage that you can actually see that the load is working. The suggested bulb will work fine for 4.8 - 6 V Rx packs.

There is absolutely no need to buy 1% resistors unless you plan to operate several loaded volt meters and want to compare measurements between them.