On Mon, 31 Aug 2020 00:35:48 +0100, Chris <xxx.syseng.yyy@gfsys.co.uk>
wrote:
>On 08/31/20 00:16, John Robertson wrote:
>> On 2020/08/30 3:57 p.m., Chris wrote:
>>> On 08/29/20 03:34, Tabby wrote:
>>>> On Saturday, 29 August 2020 01:38:09 UTC+1, Chris wrote:
>>>>> On 08/28/20 23:21, Sjouke Burry wrote:
>>>>>> On 28.08.20 20:50, Chris wrote:
>>>>>>> On 08/27/20 01:30, Tabby wrote:
>>>>>>>> Cart with 2x 12v 33Ah progolf AGM lead acids. 1.5 years after
>>>>>>>> fitting
>>>>>>>> new batteries the available range is down to below 10%. I'm not
>>>>>>>> clear
>>>>>>>> what's gone wrong.
>>>>>>>>
>>>>>>>> The charger in use has been a cheap chinese one with 2x13.7v=27.4v
>>>>>>>> output. Single stage charging only. It has always been promptly
>>>>>>>> charged after use, and never run below 50% charge.
>>>>>>>>
>>>>>>>> I checked the battery voltages after charge, they were 13.6& 13.8v.
>>>>>>>> Charged each battery independantly to 15.2v, which took maybe
>>>>>>>> half an
>>>>>>>> hour or so. No range improvement.
>>>>>>>>
>>>>>>>> When apparently flat the batteries read, offload, 12.3v& 12.8v. I
>>>>>>>> expected to see lower.
>>>>>>>>
>>>>>>>> What's going on here?
>>>>>>>>
>>>>>>>>
>>>>>>>> NT
>>>>>>>
>>>>>>> The data sheets for the better brands of the gel cell types have
>>>>>>> a graph showing expected life vs number of charge / recharge
>>>>>>> cycles. Typical design life for ups float applications can be as much
>>>>>>> as 10 years, but under regular cycling, can be<< 5 years.
>>>>>>> The deeper the discharge, the more detrimental the effect.
>>>>>>> Carts must hammer batteries pretty hard, especially if they skimp on
>>>>>>> a/h capacity to keep costs down. 38ah doesn't sound like much for
>>>>>>> what must be a 1/2 to 1hp motor, at 24 v, 1hp ~= 30 amp, then you
>>>>>>> have the much higher startup current. You get what you pay for, but
>>>>>>> Yuasa at least have different optimised types depending on type of
>>>>>>> service.
>>>>>>>
>>>>>>> I would put in bigger batteries, say 100 ah might work a lot
>>>>>>> better...
>>>>>>>
>>>>>>> Chris
>>>>>>>
>>>>>> And dont forget to buy a high quality computerized charger.
>>>>>> A cheap bad one wil sulfide the batteries in notime.
>>>>>
>>>>>
>>>>> Fully charged terminal voltage is critical as well, typically 2.3
>>>>> volts per cell max, but the data sheets will have voltage vs
>>>>> temperature curves. Overcharging increases gassing which should
>>>>> normally be minimal. The UPS people have years of experience of
>>>>> that, as opposed to consumer electronics product, where the charger
>>>>> often looks like an afterthought...
>>>>>
>>>>> Chris
>>>>
>>>> AIUI gassing is not an option for AGM. That rules out most chargers
>>>> on offer. UPSes have a terrible record of battery abuse.
>>>>
>>>> I might have to take the idea of making a charger seriously, I've
>>>> never found one that does what's needed. Not that it's difficult,
>>>> 240v 24v multistage AGM charging with temp comp.
>>>>
>>>>
>>>> NT
>>>
>>> Float, or end of charge trickle is critical, as is the voltage.
>>> Normally, ups batteries are float charged at a low current
>>> continuously, but one manufacturer has patented the idea of
>>> disconnecting the float charge until the voltage reaches some
>>> lower level, then topping up, rather than a continuous float
>>> charge current. Apparently, it does improve cell lifetimes, but
>>> no direct experience here.
>>
>> How could that idea be patented? Seems obvious that many battery
>> charging systems cut the power when they reach a preset voltage, then
>> energize again when the voltage falls to a certain point. All I can see
>> them patenting is the particular electronic process, but automobiles
>> have been using this since alternators and generators first came out to
>> charge the battery. I am sure the process predates that application too.
>>
>>>
>>> Not too much trouble to build a charger using such ideas,
>>> perhaps with a micro to manage it all, so long as it's not
>>> commercial...
>>>
>>> Chris
>>
>> John (I have never applied for a patent, and am unlikely ever to want to!)
>>
>
>Chargers for ups systems don't cut the power, but keep a small current
>float, ma, to make up for losses, whereas the idea is to switch off
>the charge completely until the voltage has dropped to a defined lower
>level, then re charge to the original end of charge level. Apparently,
>this does improve cell life and helps to equalise the individual cell
>voltages, a serious problem as battery stacks age. No reference,
>sorry, but it may have been APC...
>
>Chris
We were doing the Re-Float thing you just described in your last post
at OutBack Power Systems in our inverter/charger almost 20 years ago.
Yes, it supposedly does increase battery life if you don't need to
Float all the time. It will draw as much current as necessary to
hold the battery and loads, if any, at that voltage.
I wonder how long ago this patent was ? I haven't heard of it being
patented. But since patents are only good for 20 years now in the US,
the prior art would be real close in this case.
boB