2 banks of batteries or just 1 big one?

[Ben Plant]

Thanks very much all, 1 bank it is,

 

Cheers,

 

Ben

Heron

[DeanS]

I thought it was 4

 

dont tempt me.

[Rufford]

One bank is best, however the most efficient use would be to have two largish banks and switch between each bank, run low on charge, switch consumption to other bank, charge the bank to 80%ish using a generator and then put it on solar panels for a bit to get it up to 100% while you use your other bank, then switch and repeat. However it tends not to be practical to do that.

[boots]

Not sure why that would be more efficient? Surely the most efficient way would be to use the elec from source rather than load it into a battery and then use it from the battery which brings into play battery inefficiencies? Is the most efficient way is to connect any load to the source, and allow any excess to put into charging - I.e. A single bank?

[bottle]

One bank is best, however the most efficient use would be to have two largish banks and switch between each bank, run low on charge, switch consumption to other bank, charge the bank to 80%ish using a generator and then put it on solar panels for a bit to get it up to 100% while you use your other bank, then switch and repeat. However it tends not to be practical to do that.

 

but....no it would not, if you ran exactly the same loads for the same time, each bank would be taken down to a lower SOC so would require longer charging.

 

also as the batteries would be taken to a lower SOC they would age quicker and so would need replacing earlier.

 

Discussion open will now get the popcorn.

[nb Innisfree]

 

but....no it would not, if you ran exactly the same loads for the same time, each bank would be taken down to a lower SOC so would require longer charging.

 

also as the batteries would be taken to a lower SOC they would age quicker and so would need replacing earlier.

 

Discussion open will now get the popcorn.

That basic fact is often missed.

[pelicanafloat]

Edited as I think my post unsuitable to remain :-)

Edited October 11, 2013 by pelicanafloat

[WotEver]

 

The lowest our batteries have been is 11.9v we've never actually run out of power, if the batteries reach 11.9v...

 

... we have irrevocably damaged them because that is 90% discharged.

 

I'm surprised that no-one else has picked up on this.

 

Tony

[Ex- Member]

 

... we have irrevocably damaged them because that is 90% discharged.

 

I'm surprised that no-one else has picked up on this.

 

Tony

 

Hi Tony

 

Well this has only occured on a couple of occasions over the past 2 months so not a regular occurrence. We have our home made built in generator nearly finished, this is going to have an automatic cut in at around 60% soc during the day time.

 

We also have an additional 240w panel going up this week with a high tilt to glean winter low sun.

 

We're actually getting in 26.6 amps as i type and was well over 30a an hour ago, batteries already reading near the full mark. I Would guestimate that we are generally over 50% SOC 85% of the time. Batteries are now well over a year old, last 3 monthly top up they needed just 1 litre of water for the 6 batteries 700a so I think their holding up pretty well overall.

[WotEver]

Indeed, they sound like they're doing very well

[smileypete]

Can I hijack this discussion please.

I've just about got my head around all the in and outs of batteries, most of it gleaned from this forum.

For historical reasons we have two domestic banks. One is 6 full traction cells, giving 900 amp/hr @c5. The other is 440 amp/hr of Lifeline AGM.

As the experts on here will know, the charging routine is different for the different batteries. Because of this I charge the tractions from the combi and the Lifelines from the 12V alternator, with a Sterling controller.

After that ramble, what I would like to know is, can I link the two banks using my 1-2-both switch or is that a no no?

 

If they're linked and discharged together there's a strong possibility the AGMs will discharge far quicker than the tractions, due to their much lower internal resistance, and may even get over discharged, or at least get a disproportionate amount of wear and tear.

 

A DC clamp ammeter will tell at a glance how much current is coming from each set of batts. Or you could discharge them normally, separate them, check the resting voltage of each set and translate it to SoC.

 

As for the OPs question I'd say that for an off-grid liveaboard, having a split-able bank gives more possibilities for charging and equalisation charging.

 

So for off grid liveaboards:

Single bank = more efficient discharge, but long weekly engine/genny runs in winter or without solar.

Split-able bank = less efficient discharge when not joined together, but may be possible to avoid long genny/engine runs.

 

Also for proper semi traction batts like T105, US2200:

Shallow discharge = quicker but less efficient recharge, a little bit more batt life but not that much.

Deeper discharge = slower but more efficient recharge, a little bit less life but again, not that much.

 

Bit more reading:

http://windandsunpower.com/Download/Lead%20Acid%20Battery%20Efficiency.pdf

 

cheers, Pete.

~smpt~

Edited October 10, 2013 by smileypete

[Tony Brooks]

 

If they're linked and discharged together there's a strong possibility the AGMs will discharge far quicker than the tractions, due to their much lower internal resistance, and may even get over discharged, or at least get a disproportionate amount of wear and tear.

 

smpt~

 

 

So given that you say "strong possibility" - so a bit like my reply - why do you think that?

 

As a battery discharges its terminal voltage will fall so supposing the AGMs did discharge faster their voltage would not be sufficient to push as much current out of the batteries as the higher traction cells. This means the AGMs would then discharge less fast while the traction ones discharged faster. This suggests to me that they would both end up at a similar state of charge UNLESS for any given state of discharge each type provided a different terminal voltage. I can see that as Gibbo says some AGM acids are not just sulphuric this could be the case but even then would they still not tend to even their discharges out.

 

I can see that the charging side of things may be different if both types accept a charge at any given voltage at different rated but again I feel they will even themselves out as one's terminal voltage rise above the other. I can see that you could ruin one type if the charging voltage had to be reduced to suit the other but again would that not only imply a longer charging time to get both banks to the same level of charge.

 

Discuss:

[ROBDEN]

 

 

So given that you say "strong possibility" - so a bit like my reply - why do you think that?

 

As a battery discharges its terminal voltage will fall so supposing the AGMs did discharge faster their voltage would not be sufficient to push as much current out of the batteries as the higher traction cells. This means the AGMs would then discharge less fast while the traction ones discharged faster. This suggests to me that they would both end up at a similar state of charge UNLESS for any given state of discharge each type provided a different terminal voltage. I can see that as Gibbo says some AGM acids are not just sulphuric this could be the case but even then would they still not tend to even their discharges out.

 

I can see that the charging side of things may be different if both types accept a charge at any given voltage at different rated but again I feel they will even themselves out as one's terminal voltage rise above the other. I can see that you could ruin one type if the charging voltage had to be reduced to suit the other but again would that not only imply a longer charging time to get both banks to the same level of charge.

 

Discuss:

 

Have I missed something? Where is Gibbo? Well I hope.

[smileypete]

 

 

So given that you say "strong possibility" - so a bit like my reply - why do you think that?

 

As a battery discharges its terminal voltage will fall so supposing the AGMs did discharge faster their voltage would not be sufficient to push as much current out of the batteries as the higher traction cells. This means the AGMs would then discharge less fast while the traction ones discharged faster. This suggests to me that they would both end up at a similar state of charge UNLESS for any given state of discharge each type provided a different terminal voltage. I can see that as Gibbo says some AGM acids are not just sulphuric this could be the case but even then would they still not tend to even their discharges out.

 

I can see that the charging side of things may be different if both types accept a charge at any given voltage at different rated but again I feel they will even themselves out as one's terminal voltage rise above the other. I can see that you could ruin one type if the charging voltage had to be reduced to suit the other but again would that not only imply a longer charging time to get both banks to the same level of charge.

 

Discuss:

 

Well, if lyraboat has spent £££££££££ on 900Ah of tractions and £££££££££ on 400Ah of AGMs, not to mention combis and other stuff, I'd suggest that spending a few £ on a £25-40 DC clamp ammeter would go amiss if he hasn't got one already.

 

Having got one it's an easy job to see how much current is coming from each set when both are discharging together into different loads from various SoC levels, maybe lyraboat could post back and let us know?

 

For battery issues and questions there's a great source of info in The Battery FAQ and manufacturers websites such as US Battery and Trojan Battery, and last but by no means least by actually doing some hands on measurements. (I'm surprised at some of the ideas and theories mentioned on here that end up getting quoted as gospel, because no-one ever checks them out...)

 

I'm all for pointing people towards self sufficiency, and not providing an instant detailed answer on a plate a la Gibbo, (teach a man to fish etc etc...). But it seems a lot of people don't want any self sufficiency, judging by the almost daily wails of mourning for our departed and dearly beloved great Gibbo.

 

cheers, Pete.

~smpt~

Edited October 11, 2013 by smileypete

[tommytelford]

Big battery banks are great IF you have the capability to keep them charged. 920ah requires a lot o input. A 85amp alternator running at a nominal 70% will require your engine to be run for around 15 hours to charge from flat, assuming nothing is switched on during charging.

 

Sorry back of a fag packet calculations.Bearing in mind the batteries you are talking about are not deep cycle batteries they should be kept fully charged it seems that this capacity is a bit over the top,

[nicknorman]

Although I wouldn't advocate paralleling different types of battery, I do think the problem lies with the charging, not the discharging. All these batteries are basically lead acid and have a similar voltage /SoC profile. Even if one set has lower internal resistance and might initially take the lion's share of the discharge, this will only be a short term effect as their voltage drops faster than the other set - this will result in the other set, now at a slightly higher voltage, passing an increasing proportion of the current so it will all balance out.

 

Recharging is a different matter - towards the end, anyway. AGMs can easily be damaged from overcharging, whereas tractions seem to like a good belt of overcharging provided the water is kept topped up.

[George94]

As they are very different types, I would be inclined to keep them separate pro tem. In fact, I would try to store one bank, use the other until it needs replacing, then replace it with the stored one. AGMs can be stored a long time.

 

Not sure that such a big bank is a good idea anyway. Lots of solar is the key in summer, minimise consumption at night, and use a small generator for a long time rather than a big one for a short time. That way you can use genny power rather than battery power (cheaper because no charging losses), and also give the batteries plenty of time to get back to 100% at a low charge rate.