Any wet cell battery experts out there?

[Omaroo]

Hi all :)

Jenny has just scored 18 x 6v 70AH wet cell batteries that are usually for submarine duty. They've been written off as near-new by her company and she is able to get the whole lot.

Question - how do you keep these in good condition when we're not yet ready to deploy them at our property?

My guess is to gang them up by connecting them together in set of two, in serial, to make 9 x 12v banks. Is it kosher to then join these 9 x 12v banks in parallel, resulting in a conglomerate bank with 630AH capacity? Can this huge bank then be trickle-charged by a normal car battery charger that charges at 15 amps and will trickle when the system reaches 14-odd volts?

TIA

[acropolite]

It's fine to join them together as banks of 12V in fact it's common practice. Give them a good charge, 14 volts or even a little higher is acceptable, normal charge voltage for lead acid is around 2.35 V per cell which equates to a little over 14 volts on a 12 Volt bank. Boosting to a slightly higher voltage at the end of charge is beneficial as it will bubble the electrolyte slightly and circulate it, preventing stratification of the electrolite, which is a major cause of premature failure especially at higher temperatures. The normal car charger will be OK but don't expect the rating to be anywhere near accurate as battery charger manufacturers have a habit of grossly exaggerating charge outputs. The charge rate can be fairly modest, for example I charge a similar sized (600+ AH) lead acid bank with solar panels with output of 8 amps, the solar regulator terminates charge at 14.2V floats at 13.8V and occasionally (once a month) boosts to around 15V for a simgle cycle.

Once the batteries have reached full charge then maintain them at 13.8 to 14 Volts and keep an eye on electrolyte levels. When you do start to use them, their service life will be maximised if you limit discharge to around 30% of capacity.

[Dujon]

Chris,

Most lead/acid batteries, wet or sealed, will store well when charged ( the preferred method ) for significant lengths of time. Unlike some other rechargeable batteries (e.g. Ni-Cd) which are recommended to be discharged prior to storage. In other words, unless you are intending to store the things for, say, 12 months or more, there is no need to worry about them provided that they are fully charged at the time of moth-balling.

Charging two batteries in series should not be a problem - assuming that the charger used is not too small. Charging them in parallel (i.e. two banks in series which are in turn in parallel with another similar set) I'd be a bit wary about. The reason for my concern is that, should the two sets not be identical, you could find that one set is always (or at some time) trying hard to charge its mate). This can be overcome by constructing or purchasing some form of regulator/balancing device. I think that you will find that these are often used in situations where an 'active' battery is used in parallel with a back-up set of cells.

I am not an expert, Chris, so do a bit of research. There is a company in Sydney - Master Instruments - which specialises in batteries in many forms. It might be worth a 'phone call.

Cheers

[Omaroo]

Thanks heaps Phil & John :)

All the batteries are physically identical, but may not be chemically.

I think I'll do the nine 12v sets and charge each bank individually for safety's sake at the moment. When they eventually make it down to the property we'll decide if we go solar, wind, micro-hydro or a mix. My workshop car battery charger is a reasonably good one (read: not a SuperCheap special) so I'll see how it goes.

Wow - the fun starts - carrying them all :(

Thanks again!

[Glenhuon]

Wooo!! nice score Chris :)

As previously stated I'd would be wary of ganging up the pairs. Probably best to bring all pairs up to full charge and give them a trickle refresh every couple of weeks. A small solar panel would be ideal for this. Thats what I intend doing with the pair of 12v 33AH Gel Cells I scored from my ladies wheelchair.

Cheers
Bill

[acropolite]

Actually most don't, self discharge on Lead Acid varies from about 3 to 5% per month for solar grade batteries (e.g. BP PVstor batteries acknowledged as one of the best made are 2-3%) and can be significantly higher for deep cycle batteries, they may seem to hold up OK over the period but they are gradually sulphating.

[Outbackmanyep]

Thats True acropolite,
Lead/Acid batteries will sulfate when not used, don't store them on concrete either!
I'd also buy a hydrometer if you can access the cells, as this is the ONLY means to make sure your battery is fully charged, green lights and bells and whistles on a charger do not necessarily mean a fully charged battery!

[Kokatha man]

Hi wet cell man - as a fella thats been, in the past, entirely dependant on batteries for all lighting and power in remote areas (mainly wind, some solar) I'll depart from my normal stirring, flippant thread-posting nature and give you my (educated and experienced) 2 bob's worth!

First of all I'll presume you meant 700 Ah capacities triple cell batteries (bloody small subs if they're operating from 70AH units!) - but having been unable to avoid that comment I can state categorically that there is no problem/danger in paralleling up 2 sets to create (nominally) a 12 volt 1400Ah system - though if they are indeed 70Ah units series configuring them into 2 banks of 12 volt 70Ah units will only give you 140Ah capacity.

When you parallel batteries (which are, technically, a series of individual 2 volt cells) you effectively double the capacity - presuming the two sets are of equal "storage capacity." If they aren't, you'd run into problems like discharge between the "pairs" but if they are all the same types that is not a problem. Series connections raise the output voltage (ie two 6 volt units where the negative of one unit is joined to the positive of the other and the resultant "unjoined" terminals become the composite unit's neg. and pos.) but the storage capacity (Ah) remains the same as one individual unit.

Those types of batteries (rather the individual cells) are usually rated at what they call the "10 hour rate" - meaning that if they are 700Ah jobs they (technically) should deliver 70amps for 10 hours without significant drop in output voltage. (I have, in another life, tested hundreds of similar cells used in remote area exchanges for what was PMG/Telecom/Telstra.)

This current (70amps) should also be the maximum charging rate, and to ensure the longest life from the batteries they should be kept at or near fully charged permanently - this is known as "floating" the batteries.

Trickle-charging them once fully charged is the go here: and whilst, as someone has already commented, some recommend "gassing" the cells occasionally, this is not really advantageous except if the batteries have been allowed to run down and have sat discharged or semi-discharged for some length of time and become somewhat "sulphated". This is because this sort of treatment (giving them a boost when they are fully-charged), promotes plate disintergration and even though these types of batteries have a large capacity for charge and a large "collection" area at their bottoms to store disintergrating plate material it is unhealthy for the batteries.

If the battery charger you are using is a decent one (well regulated) then if the trickle charge is around a maxmum of 2 to 3 amps when full charge is reached it can be left on continuously without overcharging the setup - but as someone has already stated, a hydrometer is essential to keep the electrolyte at around SG 1250 (actually 1.25 but written as "1250" and remember to maintain the level up to the top marker Some applications advise 1260 SG - but not for these units and your proposed application. Naturally electrolyte level is maintained with distilled water.

As for placing them: a good pallet (or two) makes a great support on a conc. floor in a well ventilated room/shed - and finally, if they are the clear plastic type cells, I should add, faced with a cracked and leaking cell that needed emergency aid once, I found that "Plastibond" was the only material to effect a repair without draining the electrolyte - which you can't do, because the plates will heat up, "steam" and self destruct!

Regards, Kokatha man.

[Kokatha man]

Sorry Oomaroo - I think I've been at the pc too long today! The 2nd paragraph of my first reply should read thus:

If you series connect two 6volt batteries as I described to create a 12volt battery as stated the capacity remains the same as for one: ie, if, as you state, they are each 70Ah jobs the storage capacity remains 70Ah. (As stated rather facetiously) I am amazed at them being only 70Ah for submarine batteries - their physical size would be similar to the old 6volt VW Beetle car batteries (if you're old enough to know what I'm talking about!)

However, presuming they are 70Ah units : connecting two together will give you 12volts and if you "construct" all 18 batteries into this configuration to give you nine 12 volt 70Ah batteries and you can then parallel all these individual 12volt sets together to give you the 12volt 630Ah unit you desire.

Assuming they are rated at the 10 hour rate that means the maximum charge rate should be below 63amps - preferably around 30-40amps: though your 15amp charger should do the job. With a 15amp RMS maximum charge rate charger it would take approx 80-100 hours to fully charge a flat 630Ah battery bank (taking into account battery efficiency etc which is best presumed at about 60%)

As stated before, if the charger you use will only "trickle" at about 2amps or so the batteries will be fine - and whilst you could just charge them up and leave them fully charged as someone suggested it is definitely not the best to then leave them such for any extended period. The other option to my suggestion of leaving them on trickle at about 2amps continuously is to fully charge them and then every month trickle them for a day or two.

Make sure all your "straps" (and all the terminals on the batteries) that you use to series and parallel batteries together are cleaned/polished before tightening and greased afterwards - there are lead connecting "straps" that you can obtain for the purpose if you don't already have said.

Regards, Kokatha man.

[Omaroo]

Thanks Kokatha Man :)

Yes, they are intended for submarine duty - but not as drive batteries. I believe that they are normally used for UPS duties on some of the more critical systems.

[Dujon]

acropolite, Kokatha man and, of course, Chris,

My apologies if my experience is in conflict with the facts. I have not had a problem with storing fully charged batteries over many months without periodic maintenance. Mind you (not that it should make much difference) I write about 6-volt 12AH SLA type units. Ah well, you live and you learn I suppose.

On the matter of paralleled batteries, whether seriesed with other batteries or not:

Would not any imbalance in the internal resistance of the battery(ies) in question result in an imbalance of current flow which, as a result, would produce a higher voltage on one set of cells compared with its 'mate'? Such a situation I would have thought would produce the effect of one set of cells topping-up, or at least attempting to, the other one. This would probably not be of significance if the difference is minor - but what about the situation where one battery has a catastrophic failure, say a short circuited cell? An open circuit I would assume would be of no consequence other than the lack of current available from that bank.

Your comments will be appreciated.

[Kokatha man]

Hi again all - Dujon does have some valid points in certain respects: the "sealed lead acid" batteries he refers to are far more forgiving in terms of maintaining condition and charge than wet cells (the traditional type and, I presume, the subjects in question) and yes; variations in internal resistance between cells can cause problems - which in a normal "battery" (ie a set of cells series connected) is often an associated aspect of the battery's failure (a crook or dead cell stuffing the whole thing up.)

Variations in internal resistance, and the not wholly-dependant variation in voltage (potential difference) between cells/batteries paralleled up will result in discharge from the higher to the lower but; unless "catastrophically" different as mentioned, presents no real problem in normal situations. (Obviously, these "catastrophic" situations are symptomatic of serious deficiencies within the cells/batteries.)

Presumably these batteries are in good condition (all of them) and should present no problems - though if they aren't all fine.......(but any/all of the above would create only diminished performance or failure, not the apocolypse!?!)

Lastly, electrolyte "stratafication" is an urban myth: the electrolyte, diluted sulphuric acid, is not simply an admixture of water and pure sulphuric acid (a viscous, oily compound) but an actual chemical combination of the two that produces intense ionization - a critical aspect of their suitability as the electrolyte - and the combination also creates an intense physical reaction, as anyone who has attempted to "mix" the two together in the wrong order can find to their detriment. It is most assuredly not the type of combination whereby separation of the constituents occurs or there is any semblance of a gradation in the levels of concentration between the two at various depths. Ionization is, in fact, a constantly interactive process between the water and the acid.

Hope this isn't too dry or boring, regards, Kokatha man.