dragos_cscc

My Feedback: (5)

Stupid questions for all the gurus out there. Have a 4.8V 500mAh battery that is,... lets say half way charged. Hook it up to a charger, 50mA. Now if I were to check the current with a multimeter, what would i read, the charger current or the battery current? Would the battery fully charged read 500mA. Not exactly sure how all this works, so I'm sorry if all these questions seem mediocre.

Thanks

Dragos

mr.rc-cam

If the charger is a true 50mA constant current design, then the charge current will be very close to 50mA. If the charger is a cheap wall wart type rated at 50mA @ 4.8V, then the actual current will not be so well defined. It will be what it will be, but probably somewhere in the neighborhood of 50mA or so.

Matt Kirsch

My Feedback: (21)

500mAh is the battery's CAPACITY. It's not something you can read by putting a meter on the battery. What it is is a measure of average current over time. A 50mA current over 10 hours, for example (50 * 10 = 500). You can only measure it by charging or discharging the battery.

Be careful when measuring current. You can't do it by putting the multimeter in Amps mode and touching both leads of the battery. That will FRY the meter, the battery leads, and maybe even the battery. You need to connect the meter in series on ONE of the lines, and there MUST be a load, like a battery charger or motor.

dragos_cscc

My Feedback: (5)

So to measure current you need to connect the meter in seriesl with either battery lead. Ok, now i know how to find the load and the charging current on the battery. How can I find out the battery's state of charge, without discharging it? How often should the batteries be cycled?

Thanks

Dragos

cwrr5

My Feedback: (32)

Get a good charger - like a Triton or FMA. ~$100 (roughly). There's others out there too, I'm sure everybody has their favorite! As you charge/discharge the battery, it displays everything thats going on, like the capacity, voltage, time, etc.

You can find the battery's voltage level easily. Just use a meter connected to both battery leads (+ and -). Capacity is just as Matt described, and theres no measurement for it, except for current over time(mah or ah, milli-amp-hours or amp-hours). You're correct on measuring the current, the meter should be connected in series with a load(such as a charger, or the plane/car/boat/spaceship/etc you want to use the battery in). There's really no quick way to gauge how much "juice" the battery has in it, but taking a reading of voltage will give you a good idea. it should be (and this varies) slightly higher by a volt or two than what the battery actually says it is when fully charged. Different battery types can discharge to different levels and at different rates before it adversely affects the battery chemistry.

As far as cycling the battery, I assume you're asking about the "memory effect" usually associated with Ni-cd batteries? It's actually called voltage depression, and is very easily cured by cycling(completely draining the battery to it's "safe" lowest limit, then slow charging back to normal). There's several different schools of thought on this, but there should be no reason to regularly cycle a battery unless it's abused (a LOT). If you do notice the battery voltage dropping over time, try it. If it still doesn't hold a charge, get rid of it and get a new one.

Phew! - sorry, didn't mean to get long-winded, hope this helps if you can de-cypher my gibberish!

BTW - be careful with Li-po or Li-ion(Lithium-polymer, Lithium-ion) batteries, they aren't as forgiving as other types and can easily be ruined. []

AgCat1982

One thing I believe was left out. You MUST have an Amp meter that will handle the current you expect you system to use. You have to have some idea of this already or you may have the wrong battery or esc. If your motor wants more current than your batteries can supply something usually gets damaged! If your motor wants, and the battery supplies, more than the esc can handle then the esc will burn out. Most multi-meters only measure milli amps. A few go to 10 amps. Most of these guys use an amp meter that will handle a large number of amps to see what is about to happen before something blows and/or to give an idea of the amps your system is actually using, to get the most efficient setup.

Just a few thoughts.[8D]

Good luck and happy RCing

Matt Kirsch

My Feedback: (21)

I don't know if this was addressed or not, but you can't find out a battery's state of charge without discharging it. NiCd and NiMH hold a level voltage throughout most of the discharge cycle, so you could measure 1.2 Volts, for example, and be anywhere from 20% to ~80% charged.

cwrr5

My Feedback: (32)

Both absolutely right! Thanks for the assist