Heat dissipation from battery's.
Heat dissipation from battery's.
(OP)
Hello everybody, I am here to ask a question about battery heat dissipation. I am an HVAC engineer and I revied the heat dissipation of battery's in a battery room and noticed that our contracted had mentiond two figures. As an example I will take on of the battery room,s the first was 0,08 kW and the second was 1,786 kW this is the heat load for the same battery,s but under different conditions. Now I have questioned the contractor hhow tis is possible that there is a factor 22 between the loads and I recieved the following answer.
During float charge (normal operation) battery voltage is 2,25 V/cell. During boost charge voltage is raised to 2,4V/cell which means higher battery current than during float charge. Battery has it's internal resistance. As the internal resistance gives power looses equal to P= I^2*R this means that if current increases than power looses also increase ( battery resistance is constant). So boost charge requires higher voltage what causes higher current flowing through what produces higher power looses.
This was the answer I recieved from our contractor. The questions I now got is: is a differance in 0,15 Volt per cell sufficent to produce so much additional heat? And does the answer I recieved make sence?
Thanks for your help
During float charge (normal operation) battery voltage is 2,25 V/cell. During boost charge voltage is raised to 2,4V/cell which means higher battery current than during float charge. Battery has it's internal resistance. As the internal resistance gives power looses equal to P= I^2*R this means that if current increases than power looses also increase ( battery resistance is constant). So boost charge requires higher voltage what causes higher current flowing through what produces higher power looses.
This was the answer I recieved from our contractor. The questions I now got is: is a differance in 0,15 Volt per cell sufficent to produce so much additional heat? And does the answer I recieved make sence?
Thanks for your help





RE: Heat dissipation from battery's.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Heat dissipation from battery's.
The only surprise is why there's only a factor of 4.7 between charge and float current. Your assumption about constant R might not necessarily be valid.
TTFN
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RE: Heat dissipation from battery's.
....itsmoked...is it really 40% of the energy put into charging them goes off as heat?
.....i think possibly this percentage depends on the actual bulk charging current.
Max bulk charging current is usually C/4.....where C is the Ah rating of the battery.
....but i believe cutting the charging current is better for the battery.
..hollandhvac,......do you have switched mode chargers ?..if not then this may be upping the ambient.
..........float charging may be a waste of time if youre going to use the batteries pretty soon (couple of weeks) after the Over-charge taper current threshold has been reached. -you could just switch the charger out with a relay.....and then if charger is turned off (say overnight) the battery is not discharging through the leakage reistances of the semiconductors etc.
RE: Heat dissipation from battery's.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Heat dissipation from battery's.
RE: Heat dissipation from battery's.
The 70% you are stating jimkirk is the coulomb efficiency which avoids the further losses of the charger with its typically, less than, 90% efficiency, nor the regular equalization charge cycles that are very inefficient.
hollandhvac needs the total losses I would expect.
Sealed LA have higher charge efficiency but that is because they charge at a much lower rate, often too low for commercial requirements.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Heat dissipation from battery's.
Question to IRstuff, what factor do you mean with 4,7?
Thanks so far for the answers.
RE: Heat dissipation from battery's.
RE: Heat dissipation from battery's.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Heat dissipation from battery's.
RE: Heat dissipation from battery's.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Heat dissipation from battery's.
to elaborate, float charging is just "keeping it topped up"
it is the final phase of charging and sometimes omitted.
battery charging 12v lead acid has four phases:-
1. Trickle charge: if below 10.5 V (Constant very low current)
2. Bulk Charge: when reaches 10.5V (Constant high current, max C/4 (?) )
3. Overcharge: When gets to about 14.6V...(Voltage constant at 14.6V , current monitored while it falls)
4. Float charging:- When current falls to taper current threshold (some low current). Voltage is kept constant at the float voltage say 13.8 Volts.
Stage 2 is the high current stage....but it doesnt have to be if you dont mind slow charging
RE: Heat dissipation from battery's.
Of course I was young and foolsih at the time.
RE: Heat dissipation from battery's.
Your ideal solution would be to see if the charger has a battery current limit function and if it does, what this limit is set to. Then contact the battery manufacturer and ask what the heat dissapation of the battery is at that charging current or find out the internal resistance of the battery (available on most battery data sheets) and work out the power dissapation from the equation that you have already stated.
Ups enginner for: http://www.powerups.co.uk