Numpty question re recently purchased deep cycle batteries.

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fredrussell

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So I bought a couple of 2nd hand deep cycle batteries (cheers Paul). They’re 6v T105 clones from US Battery. They are rated at 232 amp hours when new. My question is when connected in series to give 12v, do I still have 232 amp hours or do I have half that figure? Main reason I need to know is so I can put new A/H figure into my Nasa BM1 battery monitor.
 
You a 232amp hr potential when new if you put them in series for 12v, but you would only use 50% normally, so you would normally set BM1 for 115 amp hr useable
 
Daverw said:
You a 232amp hr potential when new if you put them in series for 12v, but you would only use 50% normally, so you would normally set BM1 for 115 amp hr useable
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I would set the NASA at 230Ah, and im readonably sure that iscwhat it instructs. Once it says you have used 115Ah, you "know" you have used 50%. In addirion, if you chose to place any faith in the %age charge reading, it would show 50% when ypu have used 50%

Personally, i thing the %age charge reading is as much use as a chocolate fireguard...... but the other features are good.

Dont forget to charge the bayteries to a tail current of 1 or 2% of capacity in order to be reasonably sure they are full. If ypu dont do this regularly, ypu will sulphate your batteries, and your NASA will not read correctly.
 
fredrussell said:
So I bought a couple of 2nd hand deep cycle batteries (cheers Paul). They’re 6v T105 clones from US Battery. They are rated at 232 amp hours when new. My question is when connected in series to give 12v, do I still have 232 amp hours or do I have half that figure? Main reason I need to know is so I can put new A/H figure into my Nasa BM1 battery monitor.
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Fred, in series the volts will double but the amps (and ah) will stay the same. Set the BM1 to 232ah
 
Trojan state T105s won't give full rated capacity initially. They start at a lower figure and increase to reach quoted Ah and then degrade again with age. Of course you actually get more available Ah with very low current draw and higher temperatures.

Basically, guesswork with 2nd hand clones. Use spec. initially as Paul suggested. You can tweet it later if trials show it is too high. e.g. Known current draw produces too large a percentage drop. I think the BM1 is meant to adjust itself in use but no idea how well or quickly it works.

My Smartguage just reports SOC % but no idea of actual capacity. Works well to let me know I'm not running them too low. However, I use other devices to log Ah in and out.
 
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Thanks all - I’m well aware amp hours of 2nd hand batteries won’t be anywhere near the factory figure, these are just a stop gap measure until I’m ready to get some T105’s or, if budget allows, go lithium.
 
Amp hours are dependent on voltage. If a 6V battery holds 232Ah, that is the same as 116Ah at 12V.
Presumably, you used 2 of them in series to make 12V, so you have 232Ah @12V (nominal).

With lead acid, you shouldn't go below 50% of the nominal value, so your effective capacity is 116Ah at 12V. It's up to you how you set up your monitor to reflect this.
 
roaringgirl said:
With lead acid, you shouldn't go below 50% of the nominal value, so your effective capacity is 116Ah at 12V. It's up to you how you set up your monitor to reflect this.
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I thought the point of t105's is that they are deep-cycle? Their literature says you can discharge them 80% without damage.

How good a clone the clone is, and how well they've been treated are unknowns of course.
 
roaringgirl said:
Amp hours are dependent on voltage. If a 6V battery holds 232Ah, that is the same as 116Ah at 12V.
Presumably, you used 2 of them in series to make 12V, so you have 232Ah @12V (nominal).
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Ah has nothing to do with voltage. It's a measurement of capacity.

With lead acid, you shouldn't go below 50% of the nominal value, so your effective capacity is 116Ah at 12V. It's up to you how you set up your monitor to reflect this.
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That's incorrect, the battery monitor has to be set to the cpacity of the batteries or any SOC or DOD readings are totally meaningless.
 
KevinV said:
I thought the point of t105's is that they are deep-cycle? Their literature says you can discharge them 80% without damage.

How good a clone the clone is, and how well they've been treated are unknowns of course.
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The literature gives a graph showing number of cycles in ideal conditions for various DOD.

There's big difference between cycling down to 80% and 50%. Probably 700 vs. 1200, quite a reduction. Deep discharging doesn't destroy them immediately but does reduce expected life.
 
PaulRainbow said:
Ah has nothing to do with voltage. It's a measurement of capacity.



That's incorrect, the battery monitor has to be set to the cpacity of the batteries or any SOC or DOD readings are totally meaningless.
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Power = IV
Energy = Power x Time

Energy stored in a 236Ah, 6V battery:

1) Convert to Wh:
236Ah × 6V = 1,416Wh
2) Convert to J:
1,416 × 60 × 60 = 5,097,600J

If you go through the same process for a 236Ah 12V battery, you will discover that it has twice the energy capacity.

The monitor doesn't need to know the size of the batteries as it just counts amps in and out across the shunt. Depending on the model that you have you may have choices about how the state of charge is shown on the screen, and some of these options will need the battery capacity to do this.
 
roaringgirl said:
The monitor doesn't need to know the size of the batteries as it just counts amps in and out across the shunt. Depending on the model that you have you may have choices about how the state of charge is shown on the screen, and some of these options will need the battery capacity to do this.
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Thanks for the lesson, very useful. As a marine electrician that should come in really useful.

On the other hand..............

So, if it's "just counting amp in and out", how does it use that information without knowing the battery capacity ?

If it doesn't show OSC or DOD, why does it "count amps in and out" ?

The OP has a NASA BM1, it does need to have the capacity set.
 
PaulRainbow said:
Thanks for the lesson, very useful. As a marine electrician that should come in really useful.
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As a marine electrician you really ought to know that Ah doesn't tell you energy capacity without knowing the voltage. Thank goodness there's an engineer on hand to help you out ;)
So, if it's "just counting amp in and out", how does it use that information without knowing the battery capacity ?

If it doesn't show OSC or DOD, why does it "count amps in and out" ?
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Without knowing total capacity of the battery, the monitor can display a running tally of net current flow.
The OP has a NASA BM1, it does need to have the capacity set.
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I'm not familiar with the NASA BM1, but I assure you, it is just measuring net current across the shunt and applying Peukert's equation to it with a temperature adjustment. It doesn't need to know the overall capacity in order to do any of this. The only things it can't do without knowing the total capacity are display the % SOC and the time to empty. If it won't show the tally of net current flow without knowing the nominal capacity, that's a limitation of the display itself rather than the information being unavailable to the unit.
 
roaringgirl said:
As a marine electrician you really ought to know that Ah doesn't tell you energy capacity without knowing the voltage. Thank goodness there's an engineer on hand to help you out ;)


Without knowing total capacity of the battery, the monitor can display a running tally of net current flow.

I'm not familiar with the NASA BM1, but I assure you, it is just measuring net current across the shunt and applying Peukert's equation to it with a temperature adjustment. It doesn't need to know the overall capacity in order to do any of this. The only things it can't do without knowing the total capacity are display the % SOC and the time to empty. If it won't show the tally of net current flow without knowing the nominal capacity, that's a limitation of the display itself rather than the information being unavailable to the unit.
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Every forum has one.
 
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