ACTMCRC Newsletter 30 August 2007

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ACTMCRC Newsletter 30 August 2007

Postby ford_racing » Fri Aug 31, 2007 2:06 am

Hi guys,
Next Setup will be held on Tuesday September 25th from 5:30pm in the Mallee building.
The next round for the Touring Classes is on September 25th in the Mallee Building. This will be the start of a new series..
The next round for the Clubman Classes is on September 11th in the Mallee Building. This will be the start of a new series.
There will be a fun night for all classes on September 4th in the Mallee Building.
For a break down on Touring and Clubman classes visit: http://www.actmcrc.org.au/calendar.htm

Battery Management.

There seems to be a lot to ‘black magic’ and ‘Voodoo’ surrounding battery management and how to get the best from them. After some prompting I felt is was time to document how I manage my batteries. This article will be the fist of what I hope will be a regular column in the club news letter where I give advice on technical matters as well as on driving. By the way, the views and opinions expressed are my own and are in no way indorsed by the ACTMCRC.

So, how do I manage my batteries? Firstly the equipment:
IB4200 Cells. I’ve gone with the IB4200’s as they are the standard that most people are racing with. The techniques I discuss should be applicable to other brands such as GP or EP.

Supernova Charger. A great value charger. Can charge just about anything. Includes a motor run in function that can be used for a comm lathe. The motor function also uses a ‘soft start’ function that ensures your power supply is not damaged.

Novak Smart Tray SE Was the one that everyone was buying at the time. Has a useful hold function that will hold your cells are a given voltage.
13.8v/20amp Switch mode Power Supply. More grunt then you could possibly need, just keep in mind that a switch mode power supply can be damaged by a DC motor so they can’t be used to directly power a motor. (Fans seem to be OK).

So, I get to racing; get my gear setup and start charging. The first battery will be discharged on the Supernova then, if there is time I’ll put it on the Smart ray to ensure the battery is fully discharged (to 0.9v per cell) and balanced, this will take about 20 Minutes, if I don’t have time I go straight to charging. I charge at 5amps with a 3mV cut off and a temperature max of 46deg. I try to time the charge so that the battery will be ready within 10minutes of my race. After the race I put the battery away as I don’t normally have time to do this at the track so this is normally done on the Wednesday or Thursday after racing. I discharge the battery on the Supernova to 5.4v per cell with a discharge rate of 10amps; I then charge the battery up to 30% of its overall capacity. At this point the battery is put away ready for the next time I want to use it.
So, what does this all mean?

5amp charge current is the rate as which the battery is charged. Cell manufactures indicate that you can charge at upto 6amps however I’ve seen (and had) a number of failures at this rate which is why I’ve dropped it down to 5amps.

10amp discharge current is the rate at which the battery is discharged.

3mV Cut off. This is the sensitivity of the Peak Detection in the charger. On some chargers this is not adjustable however is adjustable on most high end/racer chargers. By there nature, a peak charger will always slightly overcharge a battery, modern NiMah batteries are not tolerant of this and can be easily damaged hence the low value.

Max Temperature of 46deg. This is a useful insurance policy. Your battery may overheat for what ever reason while charging; using a thermal sensor to stop the charger will ensure that the cells are not unduly stressed.

Discharging to 0.9v. NiMah cells can be damaged by discharging to 0v.

Charging up to 30% of the overall capacity. Batteries lose charge over time, normally the older the battery the faster is loses its charge. As stated above, a NiMah battery can not be discharged to 0v, yet, if left long enough a battery will self discharge by it’s self and in some cases become unusable. Placing a 30% charge in a battery before storage ensures that your batteries will not ‘bottom out’ in between race meetings. If you’re not going to be using your batteries for a while it’s always a good idea to get them out every so often and ‘cycle’ them.

The equipment I am using is not special; you can achieve these results with most chargers and dischargers on the market. All of what I can do with the supernova can be achieved with a Novak Millennium Charger and a stop watch, Orion and LRP also make chargers that will better or match the Supernova for features. You can fabricate a discharger using Halogen globs and a Zener diode (talk to Jaycar electronics) to ensure an appropriate cut off voltage. Any discharge tray will suffice provided it has a voltage cut off to prevent deep discharging the cells. Any power supply will do provided you can give you enough current (around 5amps) at 13.8v.

Track Setup – Next Occurring Tuesday 25 September

One of the most important things the club does outside of racing is run Track Setup's. Normally held on a Sunday Afternoon or a Monday Evening before a race meeting. Track setup nights came about as a more convenient way to put together the clubs track to allow more racing and practice at actual meetings.
We don't need to run a setup for every race meeting, over the years the ACTMCRC has been racing at EPIC we have been permitted to leave our track setup most of the time, unfortunately we are still required to dismantle the track from time to time.
It's important that we don't grow complaisant and adopt the attitude that 'some one else will do it'. If you can make it out to a setup (or help when we have to pack the track up) this is a massive help to the regular attendees to these events.
To encourage attendance to the setup nights (and to help packup) the club is now offering $5 off your race fees if you help out at either two of these events. If you help out at both you get $5 off the next two times you race.
What is really helpful at about going to the setup nights is that once the track is setup you can practice. The track is pretty much available until the committee member who holds the keys wants to leave.
I know not everyone can make it to setup or help pack up after racing, but if you are available one in awhile to help out then the whole club will benefit.

Ben
ACT Model Car Racing Club
www.actmcrc.org.au
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