Hi all,
First post on here, been poking around awhile and finally signed up. Hopefully I can get some insight on this problem I've been tinkering with for awhile.
Here's the deal. I have two 12v batteries in series. I want to charge the top battery (secondary) with the bottom battery (primary). The general traffic cop of the circuit is a comparator. The comparator checks 3 things.
1. If the primary battery is above 10V.
2. If the total circuit voltage is above 20V.
3. Which battery has more voltage.
When all three of those things are true (Check #3 being the primary is higher than the secondary) then those are diode summed together to allow R9 to be pulled up. This makes the fourth comparator go low to enable the charger (DC-DC converter).
All of it works except for some oscillation on check #3. Here's my analysis so far.
Problem:
When disconnecting secondary battery from circuit, while charging, the charger goes into oscillation.
Reason:
When the battery is charging, the pri/sec comparator has a high output. Disconnecting the battery allows the charger to shoot to open line voltage, 15V. The pri/sec comparator now thinks the secondary battery, +24v/4, is charged and outputs low. This turns the charger off. Once the +24v/4 line drains below +12v/2 the comparator thinks the secondary battery is lower than the primary and outputs high, resulting in it charging and this repeats.
Note 1:
The second comparator, comparing +24v/4 and +5v is supposed to catch if the total voltage is below 20V. Since the primary can only be charged up to 15V max this is supposed to catch the absence of a secondary battery.
I was thinking if I could slow down the switching of the comparator, I could give the +24v/4 line enough time to drain below the #2 check and bypass check #3 oscillating. I can also slow down the switching of the charger FET. I don't care how slow any of this works. It could be 5 seconds between states haha! I'm just not sure how to slow it down without a bunch of extra parts.
Thanks for reading!
First post on here, been poking around awhile and finally signed up. Hopefully I can get some insight on this problem I've been tinkering with for awhile.
Here's the deal. I have two 12v batteries in series. I want to charge the top battery (secondary) with the bottom battery (primary). The general traffic cop of the circuit is a comparator. The comparator checks 3 things.
1. If the primary battery is above 10V.
2. If the total circuit voltage is above 20V.
3. Which battery has more voltage.
When all three of those things are true (Check #3 being the primary is higher than the secondary) then those are diode summed together to allow R9 to be pulled up. This makes the fourth comparator go low to enable the charger (DC-DC converter).
All of it works except for some oscillation on check #3. Here's my analysis so far.
Problem:
When disconnecting secondary battery from circuit, while charging, the charger goes into oscillation.
Reason:
When the battery is charging, the pri/sec comparator has a high output. Disconnecting the battery allows the charger to shoot to open line voltage, 15V. The pri/sec comparator now thinks the secondary battery, +24v/4, is charged and outputs low. This turns the charger off. Once the +24v/4 line drains below +12v/2 the comparator thinks the secondary battery is lower than the primary and outputs high, resulting in it charging and this repeats.
Note 1:
The second comparator, comparing +24v/4 and +5v is supposed to catch if the total voltage is below 20V. Since the primary can only be charged up to 15V max this is supposed to catch the absence of a secondary battery.
I was thinking if I could slow down the switching of the comparator, I could give the +24v/4 line enough time to drain below the #2 check and bypass check #3 oscillating. I can also slow down the switching of the charger FET. I don't care how slow any of this works. It could be 5 seconds between states haha! I'm just not sure how to slow it down without a bunch of extra parts.
Thanks for reading!