# Battery Pack - Suggestions

Hi,

I am looking for an efficient battery pack to drive 2x servos on a platform.

As described, it is possible to drive from 24-75 and the requirement is to be able to drive 5-8 hours minimal of load.

I have looked at a lithium battery that would work:

Nominal Voltage (V) - 48V
Nominal Capacity (AH) - 10AH

I wonder if anyone has experience in this area that can provide tips on different battery types that would be better alternatives.

Best Regards

1. Battery designs (lead acid, lithium etc.) have a nominal voltage for the cell. Designing your circuit to make efficient use of the cell voltage will give you the longest use out of whichever battery you choose, for example, if everything in your circuit runs at 3.3 volts, a battery that produces 3.7 volts will be better suited than a cell that produces 12 volts or 1.2 volts.
2. Servo motors will have some duty cycle, as they do not run continuously for 5-8 hours. You need to determine what your current requirement is when the servos are off, which is likely stable other than the servos, and what your draw is when the servos are on, and what your duty cycle is, the percent of that 5-8 hours that the servos are actually running.
3. Avoid "Starter" batteries, which are cheap and common lead acid batteries for cars. They are designed to start a car and remain at full charge or close to full charge most of their life. They are not designed for deep cycling the battery, that is, powering something for extended periods of time.
4. Most normal (deep cycle) batteries are rated in Amp Hours (AH) or Watt Hours (WH). Divide Watt Hours by the nominal voltage of the battery to determine the Amp Hours. Datasheets on a battery will usually show a graph for the battery at different current draws. That means, a 48AH battery will only get 48 hours from a low draw, as shown on it's datasheet. How long a battery will last drawing it at the current you need can be estimated by plotting a curve somewhere between it's min curve and it's max curve.
5. Ultimately, you will want a battery that will last 10-16 hours or more if your use is 5-8 hours. This will account for a second or third use cycle if the battery doesn't get placed on the charger, or isn't given long enough charging time, or ages etc.

I don't know if you noticed, but the servo you link has data on current draw, torque and speed for different voltages. If you run it at 48 volts DC, your max speed is reduced compared to running it at 75 volts DC. The battery you linked, although 10 AH, and no datasheet given, states it will run for 3 hours at 3 Amps. Given the data from your motor, assuming continuous duty, 153 Watts, will draw about 3.1875 Amps. So, your battery will run continuously for less than 3 hours at full speed (800 RPM) before needing a charge. I don't know that the battery manufacturer is very reputable.

Thank you Perehama for more detailed insight, it is appreciated.

I'll check for some options that will fit the setup, the link to this battery was just an example, I will look for a more trustful battery manufacturer

Best regards

rndbit:
I will look for a more trustful battery manufacturer

Reputable can have multiple meanings, but to me, a reputable manufacturer is one that provides useful product specifications about their batteries, and is fairly accessible and permanent. While reputable manufacturers are not the lowest price option, a vague description on an Ebay posting, despite the seller's rating, to me is a gamble on actual value.

Perehama:
Reputable can have multiple meanings, but to me, a reputable manufacturer is one that provides useful product specifications about their batteries, and is fairly accessible and permanent. While reputable manufacturers are not the lowest price option, a vague description on an Ebay posting, despite the seller's rating, to me is a gamble on actual value.

Hi,

LG 36V / 20,4 Ah / 734 Wh

So if I drive the servo at 36V (520 RPM), it consumes around 99W ~ 2.75Ah. Then I could drive for about ~7.4 hours correct?

So let's say that I can drive 5-6 hours in max peak to keep a little distance from max battery capacity or is that something I missed?

Best Regards

rndbit:
Hi,

https://boxbike.dk/sv/batteri-för-elcykel/224-batteri-til-elcykel-lg-36v-20-ah-734-wh.html

LG 36V / 20,4 Ah / 734 Wh

So if I drive the servo at 36V (520 RPM), it consumes around 99W ~ 2.75Ah. Then I could drive for about ~7.4 hours correct?

So let’s say that I can drive 5-6 hours in max peak to keep a little distance from max battery capacity or is that something I missed?

Best Regards

Why are you using a servo motor to power a bicycle? The batteries you are picking do not go into detail on the battery. There is a lot of detail on the package, how it mounts etc. but very little detail on the composition of the actual battery.

Perehama:
Why are you using a servo motor to power a bicycle? The batteries you are picking do not go into detail on the battery. There is a lot of detail on the package, how it mounts etc. but very little detail on the composition of the actual battery.

Hi,

I do not use servo motor to power a bicycle :), I think these batteries for electric bicycles seem good because they are quite compact and lightweight. Agree, very little information.

rndbit:
I do not use servo motor to power a bicycle :), I think these batteries for electric bicycles seem good because they are quite compact and lightweight. Agree, very little information.

These are not batteries. They are products containing batteries. They are not compact and lightweight when compared to a battery. They add to a battery an aluminum housing and mounting bracket. So, what makes a lightweight battery that can deliver 24-75 volts? As battery voltages vary with charge, the voltages given are nominal (average) only for the purpose of classifying the battery apart from others. Although there are a lot of battery compositions, I will discuss two.
Lithium Ion - There many chemical compositions all marketed as Lithium Ion. They differ slightly in cell capacity, cell voltage, energy density etc. The most common among these is Lithium Polymer (LiPo) which has a cell voltage of 3.7. Generally speaking, Lithium Ion batteries have the highest energy density, making the most compact and lightweight batteries, best suited for low power draw (milliamps).
Lead Acid - There are many chemical compositions marketed as Lead Acid, but the most common are "Gel" and AGM. Gel cell batteries are the more common deep cycle lead acid battery, with a cell voltage of 2.7, they come in a battery (hence the term) of 12 volts, 24 volts, 48 volts etc. While not a energy dense as LiPo, you will find much larger battery capacities better suited for higher currents (amps).
Since your application seems more suited to Lead Acid, I would recommend looking at one of the batteries from UPG. Unless you need all the aluminum and bracketing, getting down to the actual battery specifications will help you better find what you are looking for.