A list of battery charging figures

[WotEver]

As we know it takes a reasonably fixed amount of time to recharge regardless of the charger, especially for the latter part of the charge.

 

So your battery starting at 75% is going to take x hours.

 

You battery at 50% is going to take y hours to get from 50% to 75%. It is then going to take the same x hours to get from 75% to full. So the second battery takes x + y hours to recharge. Even though y is much less than x, x+y is still longer than x.

 

Of course the above presumes chargers scaled to the bank size, or at least able to supply all demanded current from 75% upwards, but even if not I still think the same logic applies, just to a slightly lesser extent. I can't envisage any circumstances where the bank at 50% would charge quicker.

 

Okay, folks, update time....

 

Nick was right and Tony was wrong.

 

In summary, regardless of the bank size, a fixed amount of discharge will take exactly the same length of time to replace.

 

So if you use 50Ah then whether your bank is 100Ah or 500Ah then the time taken to recharge to 100% will be identical.

 

When I thought deeper about it, it makes perfect sense. 2 x 200Ah batteries will each have half the DoD of a single 100Ah battery for the same usage, so all my waffling about fewer Ah going into the battery was nonsense.

 

Apologies for any confusion.

 

Tony.

[ditchcrawler]

 

Okay, folks, update time....

 

Nick was right and Tony was wrong.

 

In summary, regardless of the bank size, a fixed amount of discharge will take exactly the same length of time to replace.

 

So if you use 50Ah then whether your bank is 100Ah or 500Ah then the time taken to recharge to 100% will be identical.

 

When I thought deeper about it, it makes perfect sense. 2 x 200Ah batteries will each have half the DoD of a single 100Ah battery for the same usage, so all my waffling about fewer Ah going into the battery was nonsense.

 

Apologies for any confusion.

 

Tony.

OK now what are your thought so voltage dip due to drawing 450 amps from a bank of nominal 12 volt batteries.

How much difference do you think there would be between a 675 Ah bank and a 900Ah bank

[WotEver]

OK now what are your thought so voltage dip due to drawing 450 amps from a bank of nominal 12 volt batteries.

How much difference do you think there would be between a 675 Ah bank and a 900Ah bank

 

The difference would be huge. I wouldn't want to draw 450A from anything less than an 1800Ah bank anyway, and even then only for a short while.

[WotEver]

450A is in CCA territory.

[ditchcrawler]

450A is in CCA territory.

Its only 2 hot plate,the fridge and freeze, light and TV one with the water pump

[WotEver]

Its only 2 hot plate,the fridge and freeze, light and TV one with the water pump

 

All I did was get him the figures from Google - I never suggested he could or should use that lot off batteries. Does he even have a 5kW inverter?

[nicknorman]

I take 200A for the kettle, out of 450AH. That is a lot, but it is only for a short time. If I was going to take 450A I would want at least 900 AH preferably more. Presumably the hot plates will be on for a while so definitely more!

[ditchcrawler]

 

All I did was get him the figures from Google - I never suggested he could or should use that lot off batteries. Does he even have a 5kW inverter?

Well he did say he only used two of the hotplates at a time, I am assuming he doesn't switch off the fridge and freezer or lights.

[WotEver]

Yeah, but 2 halogen rings with the fridge and freezer off and sat in the dark is still 400A.

[Loafer]

I take 200A for the kettle, out of 450AH. That is a lot, but it is only for a short time. If I was going to take 450A I would want at least 900 AH preferably more. Presumably the hot plates will be on for a while so definitely more!

 

Strewth. You take 450A from your Trojans? I'd never dare do that. I start the engine for Mrs Loafer's coffee machine, at 100A!

 

Maybe I should beast them a bit more!

[Loafer]

My question is:

 

If you discharge from full to 75% SOC over 24 hrs and then recharge, it'll take x hrs.

 

If you discharge down to 50% SOC over 2 DAYS and then recharge, it'll take y hrs.

 

If you discharge down to 25% SOC over 3 days and then recharge, it'll take z hrs.

 

What is the relationship between x, y and z?

 

Is z less than 3x? I would say so.

 

So I reckon then, if you discharge for longer, the first part of the charge puts more back, than in any other case. Ergo, less generator running time per %SOC used. I guess that will be at the expense of more sulphation though.

[WotEver]

Both of your conclusions are correct in my opinion.

 

Tony

[nicknorman]

Strewth. You take 450A from your Trojans? I'd never dare do that. I start the engine for Mrs Loafer's coffee machine, at 100A!

 

Maybe I should beast them a bit more!

No, just 200A for the kettle. The rest was hypothetical.

[Loafer]

No, just 200A for the kettle. The rest was hypothetical.

 

Oops, typo. I meant to say that for 200A, not 450! I still wouldn't dare do 100A!

[swift1894]

Well he did say he only used two of the hotplates at a time, I am assuming he doesn't switch off the fridge and freezer or lights.

I usually fire the genny up when the hotplate(s), Vax, washing machine etc are being used.

Really, thinking about it, it's during the evening when the TV, fridge and freezer are all on that I don't fire the genny up, then, next morning, I fire it up for the kettle, toaster, hot plate and battery charger before (hopefully) the solar panels take over the charging.

Edited February 9, 2016 by swift1894

[George94]

I am not at all convinced by all this.

 

If you take a battery down to 80% SoC (20% discharge) it will take a long time to reach full charge.

 

If you take it down to 60% (40% discharge) it will quickly get back to 80%, and then take much longer to get all the way back to 100%. This would be so even if you didn't have an intelligent charger reducing the current. The batteries themselves reduce the amount of current they take.

 

So a large bank (lower % discharge) is bound to take longer than a small bank which has supplied the same total energy. It will of course last much longer too.

[nicknorman]

I am not at all convinced by all this.

 

If you take a battery down to 80% SoC (20% discharge) it will take a long time to reach full charge.

 

If you take it down to 60% (40% discharge) it will quickly get back to 80%, and then take much longer to get all the way back to 100%. This would be so even if you didn't have an intelligent charger reducing the current. The batteries themselves reduce the amount of current they take.

 

So a large bank (lower % discharge) is bound to take longer than a small bank which has supplied the same total energy. It will of course last much longer too.

Think you should re-read this, it seem self-contradictory. Unless it is me that needs to re-read it, but I've done so 3 times now!

[WotEver]

That's following my original logic, but it's wrong.

 

Let's go back to the 200Ah and 100Ah batteries, both discharged by 50Ah. Let's assume that 75% SoC is the point at which they go into 'absorption'.

 

The 100Ah bank has to replace 25Ah in bulk before it goes into absorption. This won't take long, but in the mean time the large bank has replaced maybe 5%.

 

We now have the 100Ah battery requiring 25Ah in absorption and the 200Ah battery requiring 45Ah. However, the 200Ah battery is actually 2 x 100Ah batteries in parallel. So what we really have is 3 x 100Ah batteries, one of which is 25Ah discharged and the other two being 22.5Ah discharged.

 

Charge time will be nearasdammit identical.

 

Tony

[MtB]

That's following my original logic, but it's wrong.

 

Let's go back to the 200Ah and 100Ah batteries, both discharged by 50Ah. Let's assume that 75% SoC is the point at which they go into 'absorption'.

 

The 100Ah bank has to replace 25Ah in bulk before it goes into absorption. This won't take long, but in the mean time the large bank has replaced maybe 5%.

 

We now have the 100Ah battery requiring 25Ah in absorption and the 200Ah battery requiring 45Ah. However, the 200Ah battery is actually 2 x 100Ah batteries in parallel. So what we really have is 3 x 100Ah batteries, one of which is 25Ah discharged and the other two being 22.5Ah discharged.

 

Charge time will be nearasdammit identical.

 

Tony

 

 

Now I have to ask, what do you mean by going into 'absorption'?

 

This is defined by the charger surely, not the battery.

[Loafer]

Yes Tony, come on. What did you mean by going into 'absorption'?

[WotEver]

I mean that the charger has stopped current limiting and is now supplying its full charging voltage (14.6/14.8 whatever) at a steadily reducing current as demanded by the battery.

 

On reflection, with a 50A charger both of the banks that I described would be more or less straight into absoption anyway, with the 100Ah battery being treated pretty harshly.

 

Tony

[George94]

Do you guys agree that a battery under charge will go from 60% to 80% SoC in less time than it will take to go from 80% to 100%?

 

If so, a 100Ah battery that is discharged to 60% SoC will take less time to reach 100% than two 100Ah batteries. And less than twice the time of one 100Ah battery.

[Loafer]

Do you guys agree that a battery under charge will go from 60% to 80% SoC in less time than it will take to go from 80% to 100%?

 

If so, a 100Ah battery that is discharged to 60% SoC will take less time to reach 100% than two 100Ah batteries. And less than twice the time of one 100Ah battery.

 

I definitely agree with the first line above. I'm not sure about the bit in red though. That bit seems to be the same as the previous sentence!

Edited February 10, 2016 by Loafer

[nicknorman]

Do you guys agree that a battery under charge will go from 60% to 80% SoC in less time than it will take to go from 80% to 100%?

 

Yes

 

If so, a 100Ah battery that is discharged to 60% SoC will take less time to reach 100% than two 100Ah batteries (two batteries at 60% each, or two batteries at 80% each?). And less than twice the time of one 100Ah battery (at what starting SoC?)

 

Could you repeat the question please? Well OK its a statement so could you repeat the statement please!

[WotEver]

Do you guys agree that a battery under charge will go from 60% to 80% SoC in less time than it will take to go from 80% to 100%?

 

If so, a 100Ah battery that is discharged to 60% SoC will take less time to reach 100% than two 100Ah batteries. And less than twice the time of one 100Ah battery.

Sorry mate but that second bit doesn't make sense. (The answer to the first question is 'Yes').

 

Snipping out the middle part of the question results in

a 100Ah battery that is discharged to 60% SoC will take less than twice the time of one 100Ah battery

See?

 

Tony