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Batteries (A/B/X Class)


A solar bike's batteries can be thought of as its "fuel tank" for storing solar energy. In order to rayce competitively, it is important that you understand your batteries.

This section focuses on lead acid batteries (B-Class teams can pick from other technologies). There are many types of lead acid batteries and many companies that make them. The batteries are available in a wide range of dimensions, weights, and capacities. You need to research what options are compatible with your drive system.

One critical battery regulation is that all lead acid batteries must be sealed. Batteries that are sealed may also be called valve-regulated. They are not "wet" or "flooded". The battery manufacturer will be able to tell you if the battery is sealed. If you have any questions about a battery, please contact SBR Headquarters. Unsealed lead acids will not be approved for raycing.

The second regulation to be aware of is that the bike's battery pack is limited by weight. Your battery pack weight cannot exceed 16 kg. Keep in mind the trade-off between energy and weight. Some teams may decide to run with a lighter battery pack, while some may try to maximize their battery capacity and weight. These kinds of decisions are what make this competition exciting!

BATTERY BASICS
How do you know how much energy your batteries can hold?

Recall that power is measured in watts (and watts = volts X amps). Energy is power X time (or watts X hours, or Wh).

Unfortunately, most manufacturers don't rate their batteries in Wh, but in amp-hours (Ah). This is the number of hours the battery could deliver a certain number of amps. For example, a battery rated 18 Ah could deliver 3 amps for 6 hours or 9 amps for 2 hours. (In reality, at the higher current, the battery will deliver slightly fewer amp-hours, but let's ignore that for now.)

So how do you calculate the energy capacity of the battery?

watts = volts X amps = power
Wh = watts X hours = energy
Wh = (volts X amps) X hours = energy
volts X (amps X hours) = volts x amp-hours = V x Ah = energy
In other words, if you multiply the voltage of your battery by the amp-hour rating, you'll have it's energy content. For example, an 18 amp-hour, 12 volt battery would have 216 Wh (12 V x 18 Ah = 216 Wh).

What if you are using two batteries (12 V, 18 Ah each)? As you'd expect, two batteries will have twice the energy of one, so these two would have 432 Wh. This is true whether you connect them in parallel for a 12 volt system or in series for a 24 volt system.

Remember to check the weight to make sure the batteries still meet the Regulations! Also, it is important for you to learn about the charge and discharge characteristics of your battery pack under the conditions that you will be using it during the Rayce.




 
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