Maths for Dummie

[Nobag]

I have two 110 ah batteries about two  years old.
12.4 v in the morning after resting overnight, according to a chart  i have that is 80%. so I have used one fifth.
If I multiple 5 x amps used, does that give me remaining capacity.
5 x 33 = 165

Thanks 

[alan_fincher]

Do you mean "amp hours used" rather than "amps used"?

[Tony Brooks]

3 minutes ago, Nobag said:

I have two 110 ah batteries about two  years old.
12.4 v in the morning after resting overnight, according to a chart  i have that is 80%. so I have used one fifth.
If I multiple 5 x amps used, does that give me remaining capacity.
5 x 33 = 165

Thanks 

 

Yes, as a guide. As discussed in another recent topic those voltages are a guide only. The actual percentage for a given voltage will vary to a degree according to temperature, battery technology and age/degree of sulphation.

 

Just noticed what Allan said - yes you need amp hours used.

Edited October 7, 2018 by Tony Brooks

[rusty69]

 

Deleted

Edited October 7, 2018 by rusty69
Talking rubbish.... Again

[Nobag]

17 minutes ago, alan_fincher said:

Do you mean "amp hours used" rather than "amps used"?

Yes I do. Sorry for that.

[philjw]

15 minutes ago, Nobag said:

I have two 110 ah batteries about two  years old.
12.4 v in the morning after resting overnight, according to a chart  i have that is 80%. so I have used one fifth.
If I multiple 5 x amps used, does that give me remaining capacity.
5 x 33 = 165

Thanks 

But of course you wouldn't want to use 100% of the battery capacity which you have calculated if you want to keep the batteries in good health.   I make 20% of 220 amp hours 44. Where does the 33 come from?

[rusty69]

1 minute ago, philjw said:

Where does the 33 come from?

That which was used?

[Nobag]

2 minutes ago, philjw said:

But of course you wouldn't want to use 100% of the battery capacity which you have calculated if you want to keep the batteries in good health.   I make 20% of 220 amp hours 44. Where does the 33 come from?

I used 33 amp hours since the last full charge. 

 

[Sir Nibble]

Four times, you have used one fifth so four fifths remain.

[Alan de Enfield]

35 minutes ago, Nobag said:

If I multiple 5 x amps used, does that give me remaining capacity.

No, it gives you the (approximate) total capacity of your bank, which is 165 Ah

 

To find out 'what you have left' you'd multiply by 4 (ie 132 Ah)

 

However you do not really want to take your batteries much below 50% of capacity, so your battery bank has 82Ah usable (50% of 165 AH)

 

All figures are approximate and depend on various factors which we know nothing about.

Edited October 7, 2018 by Alan de Enfield

[rusty69]

9 minutes ago, Sir Nibble said:

Four times, you have used one fifth so four fifths remain.

Thats what confused me (it doesn't take much). Remaining capacity left in the bank when fully charged or remaining capacity after 33Ahr used?

Edited October 7, 2018 by rusty69

[Nobag]

11 minutes ago, rusty69 said:

Thats what confused me (it doesn't take much). Remaining capacity left in the bank when fully charged or remaining capacity after 33Ahr used?

I am trying to find a figure to put into my bmv 712.

 

[rusty69]

20 minutes ago, Nobag said:

I am trying to find a figure to put into my bmv 712.

 

I wouldn't bother if it is for a %SOC reading unless you do it on a regular basis and take into account peukerts,CEF and other gobbledygook.But if you do, this is worth a read

 

https://marinehowto.com/programming-a-battery-monitor/

 

https://marinehowto.com/smart-gauge-battery-monitoring-unit/

 

But for your BMV it is the total remaining capacity you are after,i.e when fully charged

 

Edited October 7, 2018 by rusty69

[Detling]

18 minutes ago, Alan de Enfield said:

No, it gives you the (approximate) total capacity of your bank, which is 165 Ah

 

To find out 'what you have left' you'd multiply by 4 (ie 132 Ah)

 

However you do not really want to take your batteries much below 50% of capacity, so your battery bank has 82Ah usable (50% of 165 AH)

 

All figures are approximate and depend on various factors which we know nothing about.

As Alan said true current capacity is 165 amp hours so they are a fair bit down on the fictional 220 when new. But your BMV doctors amp hours, both used and charging. The Peukert value is a guess at an average adjustment of the true amps. Peukert's rules mean 1 amp is not the same as 1/10 of 10 amps on load, the higher the current the greater the effect on the battery. The BMV also uses a guess factor of the efficiency of the charging process, so 10 amps supplied for an hour may only count as +8.5 on the amp hour count.  Your batteries will have their own Peukert factor and charge efficiency so you will find that the percentage, reading will gradually drift away from the true value unless you reset it when you know the batteries are  really full (14 volts plus a steady charge current below 2 amps for about an hour).

Just seen the post above which sums it up.

[Nobag]

58 minutes ago, rusty69 said:

I wouldn't bother if it is for a continued capacity reading unless you do it on a regular basis and take into account peukerts,CEF and other gobbledy gook.But if you do, this is worth a read

https://marinehowto.com/programming-a-battery-monitor/

 

Yes I see what you mean. Virtually impossible. 

[WotEver]

1 minute ago, Nobag said:

Yes I see what you mean. Virtually impossible. 

Simplest way to establish capacity is with a SmartGauge and any Ah counter (such as your BMV). Simply see from SmartGauge what percentage you’ve used and from the BMV how many Ah that was. Simple maths gets a pretty accurate capacity. 

[rusty69]

11 minutes ago, WotEver said:

Simplest way to establish capacity is with a SmartGauge and any Ah counter (such as your BMV). Simply see from SmartGauge what percentage you’ve used and from the BMV how many Ah that was. Simple maths gets a pretty accurate capacity. 

But not then required to input into the bmv to get a %SOC.

 

 

Its a Heller va catch-22 

Edited October 7, 2018 by rusty69

[WotEver]

12 minutes ago, rusty69 said:

But not then required to input into the bmv to get a %SOC.

 

 

Its a Heller va catch-22 

No, forget the BMV SoC readings, they’ll forever be lies. Use the BMV ammeter to determine fully charged, use the SmartGauge to tell you SoC while discharging and occasionally use them both in conjunction to see how the total capacity is holding up. 

[rusty69]

1 minute ago, WotEver said:

No, forget the BMV SoC readings, they’ll forever be lies. Use the BMV ammeter to determine fully charged, use the SmartGauge to tell you SoC while discharging and occasionally use them both in conjunction to see how the total capacity is holding up. 

No need to tell me. That is exactly what i do with my SG and battery monitor. 

 

I suspect the OP is beginning to see that. 

[WotEver]

2 minutes ago, rusty69 said:

No need to tell me. That is exactly what i do with my SG and battery monitor. 

Yes I know you know. (I sound like Hilda Baker!). I was explaining it for the benefit of the less enlightened.

 

[Nobag]

Nothing is straight forward. Thanks for all the answers. 

[Sir Nibble]

1 hour ago, rusty69 said:

But not then required to input into the bmv to get a %SOC.

 

 

Its a Heller va catch-22 

I see what you did there.

[Tanglewood]

15 hours ago, Nobag said:

Yes I see what you mean. Virtually impossible. 

Mmm - in a virtual universe - virtually anything is possible.  The problem is in, what we like to refer to as, reality ...........

[WotEver]

5 hours ago, Tanglewood said:

Mmm - in a virtual universe - virtually anything is possible.  The problem is in, what we like to refer to as, reality ...........

Whereas if it was simply virtually improbable then it would be the good basis for a drive...

 

... as long as you had a good strong cup of tea.