Flood + AGM Batteries..

[Guest]

I want to connect the two of them , as one bigger 12V house bank batteries ; both are around 125 amp/hour each , new , so togheter I will about 250 amp/h. I know it is not advisable to mix , but ...the regular one is "heavy duty" , (but not deep cycle) one.
How should I connect them to (multi-port 20 amp/h each) 3 stage shore power , as one , ore each separately to better charge both?
to which should the various users ( instruments , fridge , etc.) be connected, all to have them both charged , and discharged about the same ? If I would like to connect a "Link 10" batt.-monitor , to which of them to connect it to have the best indication ( or maybe to both as a bank ?)
Thanks..

 

[pvb]

Connect them as one bank...

Whatever purists might say, there isn't too much of a problem mixing flooded and AGM batteries in a bank. Connect them in parallel as one 250Ah bank. Charge them together as a bank. Connect all the users to the bank, so both batteries share the discharge. It's the depth of discharge which ruins batteries quickly, so the larger the battery bank, the smaller is the depth of discharge for a particular usage, and the longer the life you'll get out of your batteries.

Follow the Link 10 wiring instructions religiously, and wire it to the bank. It's an excellent little bit of kit, and gives so much information to help you manage your electrics more efficiently.

 

[ccscott49]

Re: Connect them as one bank...

Not sure you are correct, I thought the two types needed different charging regimes. IMHO

 

[pvb]

Re: Connect them as one bank...

Alternators have no way of knowing what sort of battery is connected to them, and can't vary their charging regime.

 

[ccscott49]

Re: Connect them as one bank...

I may be mistaken, but I thought you had to have a special alternator controller if you had, AGM, Gel or one of the other more high tech batts. But as I said, I've been wrong about a bunch of things lately!!

 

[bedouin]

Re: Connect them as one bank...

The distinction you are thinking about is between "sealed" (i.e. maintenance free) batteries and conventional ones where the electrolyte can be topped up.

Sealed batteries, which includes all Gel, AGM and such, should have their charging voltage limited to 14.4V, whereas 'conventional' ones (sorry I don't know the correct term for them) can accept a higher charging voltage of up to 14.8V, but at the cost of boiling away the electrolyte, so they would require regular topping up. Note that many 'flooded' batteries are also sealed.

A conventional alternator is unlikely to achieve anything like these voltages so this only tends to be an issue if a smart regulator is fitted - in which case you must follow the manufacturers instructions.

 

[ccscott49]

Re: Connect them as one bank...

I knew there was a difference, just not how it worked!

 

[ccscott49]

Re: Connect them as one bank...

I knew there was a difference, just not the voltages etc. The word your looking for is "flooded".

 

[Paulka]

Re: Connect them as one bank...

The follwoing sentence is out of

http://www.sonnenschein.org/AGM's.htm

For ease of use, the majority of the top quality inverters/chargers already have an AGM charge setting programmed in so the transition to
AGM's from conventional flooded batteries or is very straight-forward.
[unquote]

To me this implies that the charging procedures for both types of batteries are indeed different.

BTW, the whole "sonnenschein" site is the best one about batteries I have found yet.

Paul

 

[andyball]

eh?

"A conventional alternator is unlikely to achieve anything like these voltages" why not? my van alternator sticks 14.8V into 150AH no problem, and it's only a little 1700 engine, so the alternator's quite small.

There's some graphs showing the "ideal" charging voltages for the various types here.... http://www.uuhome.de/william.darden/dcfaq.htm

 

[bedouin]

Re: eh?

In that case I strongly recommend getting your alternator looked at! Pushing 14.8 V continually into any type of lead-acid battery is likely to fry it PDQ. The reason most alternators are regulated to deliver 13.8V is that that is the highest voltage that can safely be delivered continuously to a battery.

Smart alternator controllers will safely boost the output of the alternator to above 14V, but they do it under a controlled regime and reduce the voltage after a period of time to prevent excessive gassing.

 

[andyball]

Re: eh?

In my experience, that's just not true.

While many modern car alternators seem to be regulated to sub 14V,older stuff,nearly every motorbike I ever worked on(100's) and my 2001 outboard (40Amp alternator), all regulate above that, I have had no frying problems ever, so they can't all be wrong.

 

[ean_p]

Re: Connect them as one bank...

I think that the difference is that the AGM have to have a very closely defined fixed voltage supply but can accept any and all current levels upto more than 50% of their ah capacity....whereas ordinary lead acid need a varied and regulated voltage / current so as to prevent plate distortion and over gassing....also the supply to the AGM has to be almost ripple free which in its self precludes all but the best quality chargers....and this dosn't mean the most expensive either.....in truth they are a difficult beast to feed but get it right and you'll have the best of batteries....

 

[hutch]

Re: Connect them as one bank...

The chances are that you will only ever charge the two up to a maximum of 85% capacity - in which case it really doesn't matter. Suggest you read/check Nigel Calder and also the West Marine Catalogue. Yes, in the long run you will may shorten the life of one or other but .. But then batteries have a mind of their own!

 

[tyger]

Re: Connect them as one bank...(Long)

General advice is not to mix battery types. On my last boat, a liveaboard, I used Lifeline AGM batteries for the house bank and heavy duty flooded batteries for the starter bank with two separate charging systems. The starter bank was charged from the engine alternator, the house bank through a Heart inverter/charger run from a generator or shore power. The Heart did not have a separate setting for AGM and on the advice of Lifeline I charged the batteries using the flooded setting. This set up worked well.

IMHO there are several reasons for not mixing battery types in the same bank. I don't know if they are relevant in your case.

1) AGM batteries are rated for more charge / discharge cycles than most flooded batteries (the first post specifically states the flooded battery is "heavy duty" not deep cycle). Since one battery in the bank will deteriorate faster than the other the bank will become a mix of "old" and "newer" batteries. The overall performance of the bank will be determined by the weaker battery.

2) The AGM battery can accept far higher charging currents than the flooded battery. If the two are in the same bank I would expect the charging current to be limited to what the flooded battery could accept. This would prolong the charging time compared to a bank of AGMs alone.

3) Flooded batteries should be "equalised" on a regular basis to maximise their life. Lifeline advised me that AGM batteries should be equalised for a much shorter period. ( Equalisation: Intelligent chargers or regualators apply a higher than normal charging voltage, with a regulated charging current, through a fully charged battery to "stir it up". The battery gasses very hard).

4) The AGM battery can withstand higher sustained discharge currents. If you use an inverter to run heavy loads (e.g. power tools) the flooded battery will be knackered very quickly: unless it is a true deep cycle battery. I learned this the hard way.

5) AGM batteries can be left in a fully discharged state for some time without lasting harm. Flooded batteries can not.

By mixing battery types you get a combination of the worst characteristics of each type.

All IMHO.

 

[pvb]

Remember I warned you about purists (nm)

 

[Guest]

Re: Connect them...2

Thanks guys for your help and advise .