Battery calculator

[Chris Lingwood]

I've trawled through most of the information on this website and Gibbo's (mostly Gibbo's tbh) and made a audit calculator. My figures might be a bit off as I've not actually measured most of them but the battery info is up to date. (btw the charge time is very simple minded).

 

htttp://www.thousandmonkeys.com/boat/Energy Audit.xls

 

Its quite interesting how it comes out. If you tune the number of batteries to the peukert capacity there's not a lot between the first 5 options. It appears that 85amp batteries are the best value if you've got room (plus adding another one is cheap). Failing that its 120amp batteries for not much more.

 

The Lucas 220 are bettered by 5*85ah by £50 for only 10 lost ah. In fact most options are bettered by 85amp as far as cost/ah goes (if you have the space). Unless there's something I'm missing.

 

Chris

 

 

 

 

 

Also I've still a couple of questions I never found answered.

 

1.

Trojan deep cycle batteries, can you, in fact, cycle them deeper? Or does the 50% rule still apply. If you can get, say 75% out of them then then they look like a good idea.

 

Gibbo suggests no, but then again he's also said that trojan batteries are in fact real deep cycle batteries where as most other ones are just starter batteries with handles on. Depends weather he means deep cycle or "deep cycle"

 

http://www.smartgauge.co.uk/50percent.html

 

If not what's so ace about deep cycle?

 

2.

Chris W also said in back in the mists of time that it was better to have bigger batteries because

 

130ah batteries give you 239ah at 1amp

110ah batteries give you 183ah at 1amp

 

Which using Gibbo's calculator is true, but irrelevant.

 

360ah at 6 amps give you 500Ah

120ah (360/3) at 2 (6/3) amps gives you 133Ah (or 500/3)

180ah (360/2) at 3 (6/2) amps gives you 250Ah (or 500/2)

 

So unless I've used that calculator wrong I can't see that it matters what size batteries you have. Although I may have missed the point...

Edited August 4, 2008 by Chris Lingwood

[Gibbo]

The Lucas 220 are bettered by 5*85ah by £50 for only 10 lost ah. In fact most options are bettered by 85amp as far as cost/ah goes (if you have the space). Unless there's something I'm missing.

 

You haven't missed anything. The reason is simple. 85Ahr batteries are the biggest seller therefore they are the cheapest per amp hour. Simple economics. I suspect the reason is that whilst we, in the inland marine world, think it is an important market, the reality is that to manufacturers and dealers it is close to being totally insignificant. The offshore, caravan and fleet vehicle markets are several orders of magnitude bigger. What they buy affects the price. What the inland marine market buys makes not one jot of difference because it is far too small. Even as a *tiny* manufacturer I see this. For every product sold into the inland marine market we sell at least 100 to offshore and 200 to the vehicle market.

 

1. Trojan deep cycle batteries, can you, in fact, cycle them deeper?

 

Yes.

 

Or does the 50% rule still apply.

 

It still applies. If cycling a normal "leisure" battery down to 25% SoC wrecks it in (say) 20 cycles, then doing the same to a Trojan would wreck it in (say) 200 cycles. ie it will last 10 times longer given the same treatment.

 

If you can get, say 75% out of them then then they look like a good idea.

 

Gibbo suggests no, but then again he's also said that trojan batteries are in fact real deep cycle batteries where as most other ones are just starter batteries with handles on. Depends weather he means deep cycle or "deep cycle"

 

If not what's so ace about deep cycle?

 

The fact that, given the same treatement as "leisure" batteries they will last about 10 times longer. If discharging a "leisure" battery to 50% each times gives 200 cycles, then a genuine deep cycle will give (perhaps) 2000 cycles. As they cost about 5 times more but last 10 times longer then they make sense. But, and it's a big but, most batteries get murdered by leaving them flat or not fully recharging. This sulfates them and wrecks them. You can still wreck a genuine deep cycle battery by the same treatment. If the batteries are being genuinely murdered then true deep cycle batteries won't last any longer.

 

2. Chris W also said in back in the mists of time that it was better to have bigger batteries because

130ah batteries give you 239ah at 1amp

110ah batteries give you 183ah at 1amp

 

Which using Gibbo's calculator is true, but irrelevant.

 

Indeed. Chris has baffled me on a few of his points, his maths (as in the sums) were always right, but often based on incorrect ideas.

 

360ah at 6 amps give you 500Ah

120ah (360/3) at 2 (6/3) amps gives you 133Ah (or 500/3)

180ah (360/2) at 3 (6/2) amps gives you 250Ah (or 500/2)

 

So unless I've used that calculator wrong I can't see that it matters what size batteries you have. Although I may have missed the point...

 

You haven't used it wrong or missed anything. 500Ahrs is 500Ahrs. It makes no difference whether it's made up from 1 battery or 5 batteries.

 

Gibbo

[Chris Lingwood]

Excellent thanks for the clarification Gibbo.

[Tim Doran]

I have had a little play with your calculator and have found it quite interesting.

 

Thanks

 

Tim