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Forum Index : Electronics : AGM battery charging
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| Lee3 Regular Member  Joined: 17/09/2014 Location: AustraliaPosts: 57 |
I've just ordered a nice AGM battery for a portable battery box for camping. The manufacturer states a maximum charging current of 24A, which we won't exceed, even if we could.... I've seen some references where 'low and slow' is the advice for charging of AGMs, with respect to keeping them healthy for longer, most just repeat the 'up to 1/3C' advice - just because it can take up to 1/3C, is this the best for it? On 240V especially, we'll never be in any hurry to charge the battery, so a low current won't hurt from a time perspective. Is this reasonable in peoples experience? Cheers Lee |
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| Warpspeed Guru  Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Wet batteries like a certain amount of fast charging, because it stirs up the electrolyte and prevents stratification, and discourages sulphation. But you are not going to reach full capacity with only a simple quick fast charge. It needs a fast charge up to some point, then the charging current needs to drop back to perhaps one tenth, so it can much more slowly reach final full capacity at a much lower rate of charge. There are many programmable "smart" battery chargers on the market that do all of that. Cheers, Tony. |
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renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
How do you plan on charging it out bush? (if at all) I use a redarc bcdc 1225d, bit pricey but after rooting a few aux batteries this bastard has paid for itself by looking after the aux batteries, it will pull 25 amps from the alt at idle compared to without the alt will only give 6A or so. Very smart and good bit of kit which can do lithium too. Seriously this topic has been covered thousands of times over, have a look at myswag and 4x4action forums, or just do a google search for auxillary battery charging. Don't get talked into getting a cheap solenoid, just cough the cash up and get an onboard smart charger. Cheers Caveman Mark Off grid eastern Melb |
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| Lee3 Regular Member Joined: 17/09/2014 Location: AustraliaPosts: 57 |
Our vehicle has a smart alternator, so a solenoid isn't an option. My question was mainly to do with the sizing of a home charger. On the optimabatteries website they claim 'low and slow' is the best for AGMs, in terms of keeping heat down and prolonging battery life. Out bush - for the near future we only have a couple of one nighters planned, so won't charge while bush, but will invest in a DCDC charger for the vehicle shortly, and solar panels if needed after that. In asking here I thought maybe there would be more knowledge regarding the care and feeding of AGMs.... |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
There should be charge rates given for your battery, just look up the specs on their web site for the battery you bought. That redarc 1225d overrides smart alternators so do look into that down the track. Cheers Caveman Mark Off grid eastern Melb |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Just had a look at your manufacturers web site, it's pretty good here Have a good read through all that. Edit, if you are thinking of adding a dcdc/bcdc (get that choice right) charger soon, why not pony up for that instead of a mains charger now and making it redundant when you get an onboard one. Everyone's situation is different though, you may have a need for a mains one for other purposes, but think about what you'll use it for after the onboard charging is added. I love my redarc, there was even an explosion in the toolbox it's contained in and a decent fire following and the little son of bitch works perfectly years later, still has the carbon on it!!! Cheers Caveman Mark Off grid eastern Melb |
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| Lee3 Regular Member Joined: 17/09/2014 Location: AustraliaPosts: 57 |
We haven't got an Optima, we bought a Fullriver, although I came across this on the optima page in googling: |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
basically just get a decent smart charger. It does the thinking for you. Cheers Caveman Mark Off grid eastern Melb |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
If you want to know more about your battery look it up on the manufacturer's web site, I don't know which one you bought but here is a good example of the info you need, or could find handy. Cheers Caveman Mark Off grid eastern Melb |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
You are right to keep your charge rate limited to the manufacturer's specifications. Being AGM they are not filled with liquid like a flooded lead acid, instead they have damp material around the plates holding a small amount of electrolyte. Whatever you do don't attempt any sort of boost or equalization charge to stir up the electrolyte, it will kill those batteries in no time at all. You need to find a charger that either is not capable of exceeding the maximum current or one that you can set the maximum amps to below the batteries limit. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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Clockmanfr Guru Joined: 23/10/2015 Location: FrancePosts: 429 |
Hi Lee3, I have had AGM's for over 9 years now, and just scrapped 1 1/2 tons of them, and got some decent SLA's, golf cart types, Marine ultra deep cycle heavy duty. I notice that recently there seems to be batteries that are listed as AGM but in reality are not. AGM's, and I mean Glass matt impregnated with acid as the separator between the plates, ....... These are normally sealed with a small expansion blowable chamber above each sell. Acid, its just damp in there, is trapped inside and CAN NOT be replenished, ie the battery is really sealed. No actual caps but the expansion chamber has a blow off cap sometimes. I have posted on the below link with my experiences, where an installer is having issues with AGM's. http://forum.solar-electric.com/discussion/353026/conext-xw-and-exploding-batteries I trust this helps. PS, I have posted a few pics in that topic link, of my BMS for AGM's that I did a few years ago. Arduino is not one of my best topics, and we maxed out at 32 batteries being monitored. I feel sure that bright sparks on here could run with this BMS and improve it? Everything is possible, just give me time. 3 HughP's 3.7m Wind T's (14 years). 5kW PV on 3 Trackers, (10 yrs). 21kW PV AC coupled SH GTI's. OzInverter created Grid. 1300ah 48v. |
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| Rabinson777 Newbie  Joined: 14/03/2018 Location: BangladeshPosts: 4 |
I am also trying to order a new AGM better for myself. |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
This kind of talk from the manufacturer is not entirely accurate. you can charge a sealed lead acid/ agm at tremendous speeds provided you throttle it back as it gets close to full. so in theory you could charge it at say 600 amps and at 80% full cut it back to 25 amps then taper the charge off as it gets close to 100%. The catch, there is always a catch! charging this fast means the voltage will be very high so there is no way you can calculate the state of charge of the battery from the voltage. therefore you have no idea when it is full. chargers that can do this count coulombs to work out how full the battery is. if the counter gets out of sync with the battery state of charge, bye-bye battery. also the faster we charge the more the chemistry resists so if I charge at 9C I will have to back off the charge rate at 85% at 4C I might push it to 90% at 2C im getting a bit cocky and I trust my counter I am going for 95% then we are back to voltage limited charging after that. what kill 99% of AGM's is the last 1% of charging, if you run your battery hard the fully charged voltage can be set higher. if the battery is always on charge and only lightly worked the same settings will boil the fluid in the battery and gas it out the pressure vent valve. if you want a battery to last, THIS is the situation we want to avoid. This is what kills most gopher batteries, when the charger is calibrated with an end voltage expecting the battery to be cycled down hard everyday and great auntie Gertrude only totters down the shops, uses 4% of the charge and wacks it back on the charger. Her battery lasts two and a half years, Uncle Harold who does 30 kilometers a day gets 7 years from his battery. if we lower the voltage so Gertie's battery does not boil then Harold's gopher will not fully charge and it will be toast in 12 months. So after that long winded explanation,  in your situation "low and slow" is a complete waste of time. You will also notice if you reduce the absorption voltage settings on the charger that will reduce the charge current (you have now got low and slow anyway)Hope this helps get your head around these cells, they are the best bang for the $ provided you dont regularly undercharge them or constantly overcharge them. The mistake most solar systems make is not factoring in the time, ie, not charging fast enough and running out of sunshine before the charger starts to taper off at the top and it never fully charges. I'm confused, no wait... maybe I'm not... |
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| Lee3 Regular Member Joined: 17/09/2014 Location: AustraliaPosts: 57 |
Thanks for that - in the end I went with a 10A Projecta Intelli-charge ( https://www.projecta.com.au/battery-charger-products/12v-automatic-10a-7-stage-battery-charger ). So far has been good - my situation is episodic use for camping trips, so I have all the time in the world to charge. This charger can be throttled back to 2A and has settings for gel and flooded too, so I can charge the car starter batts and my smaller gel battery. So far so good..... Next step is a DC-DC for the car..... |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Yahoo has pretty much nailed it. The battery does not actually need to "boil" to lose water, although temperature rise is a big factor in water loss. Its actually breakdown by electrolysis of the water into hydrogen and oxygen. Its why we must reduce the charging voltage as battery temperature increases. So you need to safely limit both max battery temperature and max battery voltage to something where water loss will be absolutely minimal or zero. Water loss is an absolute killer for any kind of sealed lead acid battery. Once it dries out it is DEAD. And its only a sticky paste in there, there is very little water to begin with. So the idea that you can really flog a sealed lead acid battery up to some point, and repeatedly get away with it, is not without the risk of shortening its life. Every time it gasses, it loses some tiny volume of water through a hidden vent, and its days will definitely be numbered. If you are really planning to regularly hammer a battery really hard, flooded wet cells are much more appropriate for that application. At the other end of the spectrum, if you have a boat or a camper van that spends most of its life parked under a tarp beside the house, then the battery needs special care when not in use. Batteries do sulphate up, and gunk can build up between the plates creating a discharge leakage path. The very best way to keep a lead acid battery healthy in long term storage is to charge it reasonably quickly, then completely disconnect it and let it completely rest, and let the terminal voltage naturally fall over time to some allowed minimum. Then reconnect the charger and charge it back up fairly quickly. This can be an automatic process, say charge at one amp up to 14.2 volts then disconnect. When it self discharges back to 12.4 volts, go through a recharge cycle. The actual voltages you choose will depend on battery type, and the manufacturers data should be a pretty good guide, as well as your own experience. A really good battery might take a week to self discharge down to the lower voltage limit. A weak battery only minutes. One amp is not a huge charge rate, but its high enough to keep an average mid sized battery healthy over very long periods of inactivity. That will be far better than putting just a very few constant milliamps into a battery held rigidly at 13.8 volts on a float charger for maybe many months at a stretch. Many sealed batteries used in burglar alarms and similar applications just sit there on constant float, and after only two or three years they are often stuffed with no reasonable capacity remaining, even though they have never been called upon to do any real work their whole life. Cheers, Tony. |
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| Lee3 Regular Member Joined: 17/09/2014 Location: AustraliaPosts: 57 |
Would there be any benefit in actually partially discharging it occasionally in place of allowing self discharge? Say with a small dummy load or similar? |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I have never done that myself. Its really counter productive if you are just trying to keep a long term stored (and out of use) battery in a healthy condition. A full proper discharge test is really the only way to know for sure how healthy a battery truly is. But its pretty severe treatment of any battery, and probably best not carried out too often. If you do decide to do the automatic charge, then rest, cycling thing, the length of the cycles can tell you quite a lot about if the battery condition is improving or deteriorating. Either high self discharge, or low amp hour capacity will both shorten the self discharge time, so its a pretty accurate indicator of overall battery health. Cheers, Tony. |
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| M Del Senior Member  Joined: 09/04/2012 Location: AustraliaPosts: 155 |
Question for Yahoo, what the heck is a gopher? Must be having a CRAFT moment Mark |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Battery Operated Gopher There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Lee3 Regular Member Joined: 17/09/2014 Location: AustraliaPosts: 57 |
Thanks - I built a dummy load (from eevblog) a couple of years back, it has been useful in testing a couple of batteries recently - with the AGM in question, it will generally get a lot of day use in vehicle in between camping trips, so it shouldn't sit idle for *too* long.... |
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