Talking Tech with CTO Morten Hjerde: What’s all this battery stuff, anyhow?

A few, (or many) words from our founder and CTO, Morten Hjerde. He’s also an engineer (read: this is a tech savvy blog article). 

Batteries suitable for The Epos lights come in many different sizes with different texts on the labels. Here is what it all means:

V or Volt 

This is the battery voltage. Actually, it is more like the nominal or average battery voltage. If the battery says 14.4 volts, its voltage will vary between roughly 16.8 and 12 volts. Highest when it is fully charged and lowest when it is empty. 

All the batteries used to be 14.4 volts, now they come in 12, 14.4, 24, 26, and 28 volts. You can use all except 12 volts on the Epos lights. 

The Epos 300 has two battery mounts but does not require that both batteries are the same type, have the same charge, or even have the same voltage.  

A or Ampere 

This is the current rating for the battery. It tells you how much current the manufacturer thinks you can draw from the battery. Some manufacturers may list one figure for a short-term load and another and a lower one for a continuous load.  

The rated amps are a max value that should not be exceeded. 

W or Watt

Watt is the power you can draw from the battery. It is simply the voltage times the amps. So, a 14.4 volts battery with a 10 amp rating can deliver 14.4 times 10 equals 144 watts. If you have a lamp that draws 300 watts, you can see that the battery is only able to supply about half of this. If you turn the brightness to full with one of these batteries, the battery would typically overload and shuts down. 

The Epos lights will attempt to avoid this by limiting the power draw to what it detects the battery is capable of. 

Wh or Watt/hours

This tells you the max capacity of the battery. How much power is stored in the battery? A large battery has a lot of Wh, smaller batteries have less. It tells you how long the battery will last. If you draw 150 watts from a 150 Wh battery it will last one hour before it is empty, If you draw 10 watts from the same 150 Wh battery it will last 15 hours before being empty.

Mount 

There are 3 types of mounts. The mount is the connector and mechanical support that holds the battery and makes an electrical connection so that the current can flow from the battery to the lamp. The V-mount is perhaps the most common. The A-mount (aka the gold mount) is also used by many. The B-mount is a new mount that improves on the older types of mounts. The B-mount is mechanically stronger than the V-mount. It standardizes the way the battery communicates with whatever gear it is connected to. 

Smart Batteries

Smart batteries have a data connection in addition to the two power connections. The Epos lights use the data connection to query the battery about its state of charge, its capacity, and other things. The Epos will then know how much power is safe to draw from the battery and how long the battery will last if it continues on the same color and brightness. 

Hot Swap

This is not a feature of the battery as such, but it is related. If a light allows hot swapping you can swap between batteries; or between batteries and the wall power without flickering.  

If you have two batteries connected to the Epos, the Epos will draw power from the strongest battery until it is empty. It will then switch over to the weaker battery. If you connect the wall power, the Epos will get its power from the mains and not use any of the batteries.  

If you disconnect the mains when a battery is mounted the Epos will switch over to the battery without flicker, provided the battery is strong enough to take over. If you run the Epos light “on full” and change to a battery that cannot deliver enough power, the light will attempt to lower the power draw instantaneously to avoid killing the battery. This means lowering the brightness. So be aware of that.