Page 461 - Battery Reference Book

45/6 Constant-potential charging
Many applications, however, require operation in envi- 1. Constant potential: 2.50-2.55 Vkell.
ronments from extreme cold to extreme heat. When 2. Limiting current: 100% of rated capacity.
batteries are likely to reach temperatures outside the 3. Charging time: 1-3h.
0-40°C range a temperature compensator built into
the charger, operating on 4mVPC per cell based on If charging at the high rate is allowed to continue
25°C is desirable. Constant-potential charge voltages excessively beyond a 3 h period, greater than normal
for various battery temperatures and modes of service amounts of gassing will occur. It is not recommended
are shown in Figure 45.5. that high-rate charging be performed in an airtight
enclosure. It is recommended that battery compart-
ments have adequate ventilation to prevent an accumu-
45.5 Two-step cyclic voltage-float lation of gases, which could reach dangerous propor-
voltage CP charging tions in the event of a charger or battery malfunction.
In general, the end of charge of the battery can be
There are applications that require a lead-acid battery determined when the charge voltage has reached the
in standby service to be recharged rapidly after a level discussed above for the various modes of service,
discharge. Under this condition a two-step charger and the on-charge current has dropped to the approxi-
would be most efficient; that is, one having a capability mate amounts shown in Table 45.4 (Eagle Picher Care-
to switch from a cyclic voltage to a float voltage. free Batteries). When the current has reached the value
In these circumstances the following conditions are shown in the table, it can be removed from the charge
recommended: source or switched to the float mode.
A charger two-step circuit for a 6 V battery is shown
1. Initial constant potential: 2.45-2.50Vkell. in Figure 45.6.
2. Float constant potential: 2.28-2.30 Vkell.
3. Limiting current: 20-40% of rated capacity. Table 45.4 Eagle Picher Carefree
4. Initial charge time: time required to reach maintenance-free lead-acid batteries:
2.50 Vlcell. current acceptance versus charge voltage
5. Float charge time: continuous.
Batteries Current (mA)
Partially recombining sealed lead-acid batteries
have the ability efficiently to accept a high-rate charge All 0.9 Ah < 20
All 2.5 and 2.6Ah
<50
without a serious sacrifice in life. In applications where All 5Ah 175
it is necessary to recharge in a limited time, the battery All 8Ah < 100
can be restored to 90-95% of full capacity within a All 12Ah <150
1-3 h period. A charger with the following character- All 30 Ah <200
istics is required:
T, TR.
2.7 r
Deep cyclic regimen
%
L' 2.6 1 cyclic regimen
/Shallow
\
% 2.4
2.3 Ti 241 7-16 signa1 Trans co
FWB, MDA952-1 Motorola
2.2 TR, MJ2955 Motorola
4,,,,,,,,, IC, MC7805CP Motorola
R,
10K POT
-20-10 0 10 20 30 40 50 R2 15 n Bourn*
Ohmite
Ambient temperature ("C) 0, F2 Sarker- Taman
Figure 45.5 Charge voltage per cell versus temperature for an Figure 45.6 Charger circuit for 12, 15 and 30Ah Eagle Picher
Eagle Picher Carefree rechargeable lead-acid battery (Courtesy Carefree rechargeable lead-acid batteries. Note that TRI should
of Eagle Picher) have an adequate heatsink (Courtesy of Eagle Picher)