Batteries and Mah.
 

Ok. I know about C ratings, Voltage, mah, and all that stuff, and I am doing a science project on LiPOs.:lol::lol:

I was just wondering about mah. So if you have a 5000mah battery, and you discharge it continuously at 5 amps for one hour, will the battery reach it's nominal voltage? If not, what will it reach? And what is nominal voltage then anyways?

Thanks in advance.

Nominal voltage of a lipo is 3.7v/cell. Fully charged is 4.2v/cell When discharging under load, 3.0v/cell is considered "dead". Taking it further down will cause damage to the cells.

Yeah I know that. I was just wondering what voltage a 5000mah battery would be at if discharged at 5000ma continuously for 1h.

I'm not sure to be honest. The voltage is dependant on your cutoff system either in your ESC or your low voltage alarm.

Mine are set at 3.4v/cell in my ESC's. So.... I guess 6.8v? If your ESC is at 3v for cutoff, then 6v.

I don’t believe the nominal 3.7V per cell is where you end up after discharging.

Rather it is intended to be the average voltage while being discharged, while under load, as I understand it. Thus along with capacity it represents the energy delivered, a useful thing to know regarding a battery application.

Some Help
 

I have experimented with 3 different 2s 5000mah batteries and the answer is... generally yes, BUT I can only convey this with the following considerations.

1. My voltage cutoff is 3.2v/cell.

2. When I CHARGE my 5000mah batteries at 5 amps AND the battery actually takes a full charge the charge time is darn close to 1 hour. The charged amount is darn close to 5000mahl. At about 50 minutes the current slows and by about 1hr 10min the balance is about finished. Sometimes I allow the balance to complete and this may take 90 minutes.

I apologize for not providing a really good answer based on science. Hopefully this helps.

Sincerely,

Technically it depends on what the manufacturer uses to rate capacity. If you want to test the capacity, put it on a charger, discharge to 3.0v/cell, and charge up to 4.2v/cell. Record how much mah went in. Now if you end up putting in 5000mah then your answer is 3.0v.

The manufacturer may have overstated or understated the value.

It's sort of like you need to actually find out the true capacity and if you do that you have already answered your question.

And I think the true min voltage of a lipo is something like 2.85v and max is like 4.22v. Don't quote me on that. It's best to work with 3 and 4.2. But the manufacturer might have used that.

Nominal voltage is the average voltage under load. If you look at discharge graphs they dip down quickly toward nominal voltage then stay there for a while. Toward the end they dip down quickly again.

Also - 3v/cell
 

It "should" be 3v/cell. However, I can't convey there is any formal industry standard in this regard.

My batteries reach their rated discharge at 3v/cell. I know this because when I charge them (yes there may be leakage) a 5000mah battery will accept about 5000mah of charge (when new).

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Thanks guys. You say that nominal voltage is the average voltage under load, but what is the load? How many amps/watts/ohms? thx

I believe it's based on a 1C discharge rate.

From a practical perspective, the average under load is likely different for various C ratings and generations of batteries. But it would be too confusing to have 3.7V, 3.71V, 3.706V, etc ratings.

When I CHARGE. Mine they start at 4.0 amps, and when they get close to get done the amps will start to drop! That's when I stip mine!!

The load is your rc car. It's the power the motor takes to spin up the drive train and get your car moving. You have a high load starting off from a dead stop. As you gain speed the load decreases. When you brake with your motor the load increases again. You can estimate loads with some math or use a datalogger but it's not really necessary. It's nice to have a ballpark idea sometimes...

Try try and estimate the load, check this out: https://sites.google.com/site/tjingu...age-amps-watts