Tech Tips

The Power to Win

by Graham Allen

Even if you are the greatest skipper since Captain Cooke you are unlikely to win a race if your wind assisted boat has no power to control the interface between you and the wind. One of the main problems to spoil your day is a boat that fails to respond to your instructions from the bank. To try to minimise this event you should have a basic knowledge of control system and the battery that makes it work.

We have all had a boat go out of control only to find the battery has gone flat. “I charged that battery all night”. But do you know how to make sure your battery has been charged correctly?

Most people will say “yes”. Well here is a reminder for those that may not be so sure.

How long should it take to charge my battery?

Well what is the battery rating (Capacity) in Mha? Batteries can be rated up to 2700Mha as found in many new NiMH battery packs. The rating tells you how many milliamps the battery will supply for 1 hour. This follows that a 900Mha battery will supply 900milliamps for 1 hour. The higher the number the longer it will last. The next thing you need to know is at what rate does your charger charge at. Different charges can charge at different rates. Have a look at the label on yours and find out. Furnished with this info you can work out how long it will take to charge your batteries with your charger.

Example

2400Mha batteries charged using a fixed rate charger of 60Mha

The Formula is battery rating(capacity)/charge current x 1.4

                                               2400/60 x 1.4 = 56 hours

And for a multi rated charger you will need to find out what is the most suitable charging current to best charge your battery. To do this, divide the battery rating (2400) by 10. This gives 240 (Mha). If you charger has not got this charge current go to the next lowest. Mine would be 180Mha. So you know now the charge current so use the formula above to find out the charge time.

                                               2400/180 x 1.4 = 18.66 hours 

Batteries can be charged at higher currents to reduce the charge time but this can heat up the cells to much shortening their life and the amount of charge they hold.

At the end of each race day should you recharge your batteries ready for next week? The general thought is if you use NiMH leave them until the time it takes to recharge them before they are needed again. Remember a trickle charger at 60Mha can take 2 to 3 DAYS to charge. It is not necessary to fully discharge NiMH batteries before recharging them as they do not build up a memory thus reducing their charge. This is not true for NiCad’s as you are advised to fully discharge them prior to recharging. Always let them cool down before re charging.

I hope this helps you reduce the problems associated with battery failure. Further info can be found on the internet along with information of what battery chargers are available.