Running a set of 12V Trojans down

simonfraser said:
Two 100Ah batteries
Using 3Ah for 30 hours over the winter weekend
Does that seem reasonable, is a third Trojan overkill ?
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I reckon a third Trojan is pretty well essential! To start with, Trojan's stated Ah capacity is at 27 C, and at typical UK winter temperatures the capacity might be 75-80% of that. So you realistically might have 150Ah capacity, assuming the batteries are in good condition and that they're fully charged to start with. Taking 90Ah out of 150Ah is too great a discharge if you want your batteries to have a reasonable life, so adding a third battery would certainly help.
 
pvb said:
I reckon a third Trojan is pretty well essential! To start with, Trojan's stated Ah capacity is at 27 C, and at typical UK winter temperatures the capacity might be 75-80% of that. So you realistically might have 150Ah capacity, assuming the batteries are in good condition and that they're fully charged to start with. Taking 90Ah out of 150Ah is too great a discharge if you want your batteries to have a reasonable life, so adding a third battery would certainly help.
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But they are supposed to be genuine deep cycle batteries!
 
VicS said:
But they are supposed to be genuine deep cycle batteries!
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Remember that 12V Trojan batteries are only rated at 50% number of cycles you'd get from their 6V range. I could never see the point in paying more to get half the projected lifespan. I bit the bullet and bought T105 even though I needed to rebuild the battery box. I would probably have bought cheaper 12V instead of 12V Trojan deep cycle batteries. Perhaps they have dropped the price and they are 50% of a set of T105s with similar Ah rating.
 
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VicS said:
But they are supposed to be genuine deep cycle batteries!
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Well, they're described as "deep cycle", but they're bottom-of-the-range Trojans and don't have a great life expectancy if they're deeply discharged. Taking 90Ah out of a 150Ah capacity is a 60% depth of discharge, and the batteries would have at best a life of around 400 cycles. Adding a third battery would reduce the DoD to 40% and virtually double the life of all 3 batteries.
 
pvb said:
I reckon a third Trojan is pretty well essential! To start with, Trojan's stated Ah capacity is at 27 C, and at typical UK winter temperatures the capacity might be 75-80% of that. So you realistically might have 150Ah capacity, assuming the batteries are in good condition and that they're fully charged to start with. Taking 90Ah out of 150Ah is too great a discharge if you want your batteries to have a reasonable life, so adding a third battery would certainly help.
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I have to agree about the extra capacity. One thing does work in your favour, the capacity will actually be increased due to the fact that only 3A is being drawn. The 200Ah figure will be for a drain of 10A over 20 hours. You should actually achieve significantly more with only 3A drain and that helps.

Downside is that the amount you can extract drops with lower temperature, win in one way but lose in another. At least you avoid reduced lifespan from higher temperatures.

A third battery will certainly be a great help.

Let's guess battery capacity down to 90% with lower temperature and you have 180Ah. Taking 90Ah gets you to 50% charge every weekend.

Even if low drain of 3A got back to full 200A (doubt it) then you are still down to 55% each weekend.

It will probably be worse as PVB says (using more pessimistic figures). Still not convinced of the value from 3x12V Trojans vs. cheap batteries if price difference is a large as I remember.
 
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pvb said:
Well, they're described as "deep cycle", but they're bottom-of-the-range Trojans and don't have a great life expectancy if they're deeply discharged. Taking 90Ah out of a 150Ah capacity is a 60% depth of discharge, and the batteries would have at best a life of around 400 cycles. Adding a third battery would reduce the DoD to 40% and virtually double the life of all 3 batteries.
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Hm, kinda my thoughts too.
But 400 cycles, only have the 3A draw during the winter, 20 weeks at the most.
That’s 20 years ....

Or am i wrong ?
 
simonfraser said:
Hm, kinda my thoughts too.
But 400 cycles, only have the 3A draw during the winter, 20 weeks at the most.
That’s 20 years ....

Or am i wrong ?
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No, it's a balance. But you also need to take into account the fact that battery performance will decline over time.
 
pvb said:
Well, they're described as "deep cycle", but they're bottom-of-the-range Trojans and don't have a great life expectancy if they're deeply discharged. Taking 90Ah out of a 150Ah capacity is a 60% depth of discharge, and the batteries would have at best a life of around 400 cycles. Adding a third battery would reduce the DoD to 40% and virtually double the life of all 3 batteries.
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Id be a bit miffed if I had bought the Trojans on the basis of what its says in the owners guide, namely

How to Maximize the Performance of your Trojan Battery
î Follow all the procedures in this User’s Guide for proper installation, maintenance and storage.
î Do not discharge your battery more than 80%. This safety factor will eliminate the chance of overdischarging
and damaging your battery.​

only to be told, "They're bottom-of-the-range Trojans and don't have a great life expectancy if they're deeply discharged."
 
simonfraser said:
Two 100Ah batteries
Using 3Ah for 30 hours over the winter weekend

http://www.trojanbattery.com/product/27tmx/

Does that seem reasonable, is a third Trojan overkill ?

Back on shore power with a sterling charger during the week
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You could mitigate the drain with solar panels. They're much cheaper than they were a few years ago and even altering your 90Ah drain to say a 40Ah drain will make a big difference. In the summer you probably wouldn't even have a net drain over the weekend with the right wattage of panels.
 
simonfraser said:
Solar panels, January in the UK :)
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I can get over an Amp out of a £89 100W panel in NI in mid winter. I've even got an Amp in autumn in torrential rain. I assume you're not in Shetland.

Have a good go at aligning the panels. And you can buy more than you would need in summer to give you useful capacity in winter. Better than trashing your batteries. :)
 
simonfraser said:
Got dark here at 5pm and wont light up till 6am, dont think the stars are gona do much, but i take your point :)
120W solar on the roof, no probs during he summer.

12.5V with a 3A load now, found this graph, sugggests i can run down to 12.0V no prob ?!

http://www.arttec.net/Solar_Mower/4_Electrical/Battery Charging.pdf
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It suggests 12V will be about 10% charged.
They are your batteries, you can do what you like.
Using them reduces their life. Life is tough like that.
Using your boat costs money, a harsh fact.

Main thing is not to leave them at a low state of charge for longer than necessary.

You could turn everything off and go to the pub? I think that was how people used to get by?
 
I think pvb is about right with his 80% figure, so taking 90ah from them is indeed going to take them down to about 40% (60% discharged). 12v will be about 40%. I'd assume that to be a rested reading, so running them down to 12v under load allows a little more margin and these are supposed to be OK down to 80% discharge, so i can't see an issue here.

This time of year on the East Coast with 100w of solar you're probably looking at about 4ah in a day.

Oh, it's more sensible when looking up figures to use the manufacturers data, or you may as well look up the ingredients of a Mars bar :)
 
However much you discharge Trojan Deep Cycle batteries, or any other battery for that matter, it is important to charge them back up to 100% every day if possible, and certainly every other day.
 
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