Leisure battery capacity

[Hog]

Just after some advice chaps - hopefully someone can point me in the right direction.

In an effort to become more self sufficient with my racing - and not having to keep scrounging the use of someone's generator to race - I'm looking at leisure / heavy duty batteries to keep me and my kids charged when we race outside.

Now both the kids are only running their SC10's with 13.5's so their battery use is not heavy. I tend to run 2 classes outside, SC10 and 4WD with 6.5's in so my use is heavier. Assuming we all practice, have 4 rounds and a final, what sort of battery capacity will I need to keep us going for the day? We use a PowerPal 4 way charger which makes things a lot easier.

I've got a 100A battery (800A cranking) which takes a good charge (and I've left it on one of these monitoring chargers) - will this be enough? Or do I need something specifically for a deep cycle? The battery I have I believe is off a tractor.

Thanks in advance.

[sosidge]

Your charger is 200W, lets assume it is running all day long (8 hours), that is 1600 Watt-hours, divided by the 12V from the supply gives you 130Ah battery capacity (roughly).

Now I doubt you will be using the charger at its limit ALL day long - I'll wager that a 100Ah battery in good condition would be enough.

If you are buying a battery, I'd buy a deep-cycle. If you have acquired a battery for nothing, then give it a try!

[dale]

The kids might take about 2Ah out of their batteries each run. You might take 3Ah out of yours (this is a bit of a guess as I run 2wd buggy and TC, but I'd be surprised if its more than that).

Total Ah will be:
5 x 2 (kid 1) +
5 x 2 (kid 2) +
5 x 3 (SC) +
5 x 3 (4wd)

= 50Ah at about 8.4V = 420 Watt Hours (50x8.4).

a 100Ah 12v battery = 1200 Watt Hours (100x12). Although you can never get all of that out, and it's generally best to stay above 50% charge as the battery life will be much longer, so I'd safely estimate 600Wh for regular usage.

The charger won't be 100% efficient; it converts some energy to heat, and runs a fan/display etc, but even so you're well within the limits of the battery.

[Hog]

Thanks chaps - will give that one a try this coming Sunday.

Did have an enormous battery in the barn - 19 inches long by 9 x 9 - would have been ideal for racing use but of 2 things:

1 - It's got a small crack in the corner and is leaking fluid, and
2 - It's too freaking heavy to carry from car to pit area!

[Gnarly Old Dog]

Dave,
I run off a 85Ah 12v Leisure battery that's a 'normal' car size battery - not one of the huge truck size batteries.
I can get 2 days racing at a national with no problems and I've been using this battery for the best part of 4 seasons now.

I do pre-charge my batteries before I go to a meeting (means I can get up later and arrive ready to practice) and Dale's calculations would sound about right to me.

There have been other threads about the pros and cons of 'normal' car ranking batteries vs deep discharge leisure ones and both parties make compelling arguments for their cause.
I'm encamped on the deep discharge battery side of things - the heavier duty plate construction in the battery means that it is designed to withstand deep discharging whereas a normal car type battery is constantly being topped up via the alternator.

But whichever way, 85Ah - 100Ah is likely to see you through - but you could trial it out with the battery you've got already before taking the plunge - even if it's only for one day - better to be safe than sorry maybe??