Quote:
Originally Posted by RedDevil
That is strange. I cannot see how charging on a low current could be bad for a battery, unless it is has a shorting cell.
What is known to limit the life of a battery is how deep you discharge it; dicharging beyond 40% SOC does indeed reduce the life of a battery; you can discharge a lead acid battery to 75% many thousands of times, but discgarging to say 10% will kill it within a few 100 cycles.
40% may well be the most economical point; beyond that the damage you do to the battery outweighs the benefit of prolonged running without alternator.
IMHO instead of charging it hard you might well focus on avoiding deep discharge.
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An update: I phoned Enersys UK this morning, but a different department in a different city from last time and got some different advice on charging Odyssey batteries that is at odds with the advice in the owner's manual.
The guy I spoke to today said that from the charging point of view, the Odyssey batteries are identical to their PowerSafe SBS industrial/telecom batteries, and will deliver similar numbers of cycles. The reason they recommend at least a 0.4C (40% of Ah rating) charge current for Odyssey batteries is because people tend to underestimate the length of time it takes a charger to achieve 100% charge. Aside from repeated deep discharges of course, the thing that really reduces the number of deep cycles one will get out an SBS/Odyssey battery is failing to achieve 100% charge between discharges, and in many applications the best way of ensuring a 100% charge is to specify a high current charger. They reckon that industrial users are able to control the charging/discharging regimes much more closely than users in 'extreme' environments and situations, so for industrial users (of the very similar SBS bateries) they specify a minimum bulk charge of only 0.1C.
There is no upper current limit, and these batteries can be recharged from 0% SOC to 95% SOC in 20 minutes. But the final part of the charge up to 100% always takes 6 or 7 hours regardless of the power of the charger, so if a user is thinking of charging 'overnight', i.e. for 8 hours, then they will need a powerful charger to avoid undercharging.
The guy I spoke to today reckoned that my existing 10A charger would be absolutely fine for charging the Odyssey PC1220 battery with its 70Ah capacity, assuming a good 10 hours per night on charge and up to 18 hours on charge after a particularly deep discharge. (18 hours will be enough to recharge a battery discharged to 100% DOD, which will never happen with a starter battery in a vehicle which is used every day, so I think I'll be alright.)
So that's one less thing to worry about. I thought I was going to have to install a larger charger and route yet more cables through the firewall.
By the way, I'm fairly close to getting this mod installed in a permanent and non-prototype-ey kind of way now. HOWEVER, ...If I were starting this project again, without having invested time and money in doing it the way I am doing it, I would do it in the following manner instead...
I would not use a DC\DC converter at all but would simply get the biggest, baddest AGM deep cycle-capable battery I could find, and put that in the rear - in the spare wheel well. I would ground that to the chassis in the rear and connect the +ve to the +ve battery terminal connector in the engine bay (or direct to the starter motor) via a fat cable and some proper fuse protection. I would dispense with the battery in the engine bay completely.
The battery I would buy would be the Odyssey PC1800, which is kind of wide and flat and the perfect shape for fitting in the spare wheel well. It is rated at 215 Ah, has a CCA of 1300A and Reserve Capacity of 475 minutes at 25A. (That's up to 8 hours of rainy roads in the dark!) I would install a 50A charger in the vehicle so it is assured of being fully charged every night. (25A would be OK, but 50A would be better.)
This set-up would add a few kilos to the vehicle's weight overall, but not a massive amount as I would be losing the front starter battery and the spare wheel. It would not be cheap, but would certainly pay for itself over time. It would be very simple, efficient, and would work well for many years. The alternator-off driving range would be HUGE, and would cover virtually any journey I might contemplate driving in a single day, whilst for everyday commutes and so on, the battery would be discharged so slightly that it would be capable of lasting for thousands of cycles.
But, I am where I am, so I'll stick to Plan A, which is a 70Ah Odyssey battery in the front and a 100Ah Yuasa YPC-100-12 deep cycle AGM battery in the rear feeding into the car's main electric system via a 12A/14v DC/DC converter and using the car's existing wiring to carry that very modest current. The Odyssey battery has a 10A CTEK charger (MXS10) attached, and the Yuasa battery will have a 25A CTEK marine charger (M300). Both chargers are temperature compensated. I'll summarise and post some pictures up when it's all properly installed.