I'm connecting 2 x 120 AH AGM 12v batteries in parallel, I'm worried about voltage leveling in case one of the batteries goes bad and I don't realise it. I have heard about Zener Diodes. has anyone installed them if so ..what size, how to, where to get. etc etc..Thanks
-- Edited by Peter and Jian on Sunday 29th of July 2018 02:56:42 PM
Jaahn said
06:00 PM Jul 29, 2018
Hi Peter and Jian
I am uncertain about what you expect to hear about zenner diodes in this context ?? But lots of people have two batteries connected in parallel with no problems and not expecting any either.
You might have read something on the internet which has caused concern, however there is nothing to worry about. It you get a multimeter and learn how to use it a bit you can check your batteries every now and again by disconnecting one and seeing they are pretty equal. Generally if you start with two new equal batteries and connect then properly they will work together till they both die of old age together years later. Sometimes it may help to individually charge them each seperately to fully charged and then reconnect them but most do not do this. Nor do people use any zenner diodes in the system that I know about.
Jaahn
-- Edited by Jaahn on Sunday 29th of July 2018 06:02:48 PM
Izabarack said
07:13 PM Jul 29, 2018
Peter and Jian wrote:
I have heard about Zener Diodes.
What would you expect a Zener diode to do? What have you been told?
Iza
dorian said
09:57 AM Jul 30, 2018
A zener diode operates as a voltage clamp. For example, a 16V zener diode would be open circuit at voltages less than its breakdown voltage (16V), whereas voltages in excess of its breakdown voltage would be clamped at 16V.
The only reference I have encountered in automotive applications is where a high power zener is connected in parallel with a battery or alternator to protect sensitive electronic circuitry from voltage spikes. Such spikes occur during "load dump" events. A load dump is when the electrical load (eg battery) is abruptly disconnected while the alternator is delivering a high charging current.
T1 Terry said
12:39 PM Jul 30, 2018
About the only method I could think of that would alert you to one of a chain of batteries in parallel failing is shunt between each battery and an amp meter showing charge running to one battery only. Rather a complex set up to notify you of a problem but apart from either never creating the problem in the first place or designing a load and charging circuit that didn't allow current to flow from one battery to the next but rather all via a central point with blocking diodes in the outward flow cables for the load side and blocking diodes on the input cables for the charging side so each battery was isolated from the group yet could contribute equally and recharge equally.
I started to design and build such a set up before I discovered the advantages of lithium batteries that you could build from individual cell. The problem was then avoided all together so there was no need to continue with the build stage of the separate battery isolator set up. If drop in individual lithium 12v batteries were used even a circuit like this would not avoid one battery doing all the work till it died, but it would stop that battery from destroying the others in parallel.
T1 Terry
Aus-Kiwi said
01:09 PM Jul 30, 2018
Wasnt she a princess ?? Lol
Jaahn said
01:14 PM Jul 30, 2018
dorian wrote:
A zener diode operates as a voltage clamp. For example, a 16V zener diode would be open circuit at voltages less than its breakdown voltage (16V), whereas voltages in excess of its breakdown voltage would be clamped at 16V.
The only reference I have encountered in automotive applications is where a high power zener is connected in parallel with a battery or alternator to protect sensitive electronic circuitry from voltage spikes. Such spikes occur during "load dump" events. A load dump is when the electrical load (eg battery) is abruptly disconnected while the alternator is delivering a high charging current.
Hi dorian et al
Just for those interested in technical things. Bosch alternators for the last 20 years have their main power diodes as zeners. Probably other main brands also. People may argue about this but it is a fact. So the zenner dioes do protect the vehicles electrical system from spikes etc which helps protect the electronics in modern cars. If you look carefully at the diagrams for the alternators you can see the difference in the symbols
So if you want high powered zenners get them from alternators. Fixed voltages though !
Jaahn
dorian said
02:15 PM Jul 30, 2018
Jaahn wrote:
Just for those interested in technical things. Bosch alternators for the last 20 years have their main power diodes as zeners. Probably other main brands also. People may argue about this but it is a fact.
No argument from me. Thanks for the info. (Didn't we discuss this before?)
I'm connecting 2 x 120 AH AGM 12v batteries in parallel, I'm worried about voltage leveling in case one of the batteries goes bad and I don't realise it. I have heard about Zener Diodes. has anyone installed them if so ..what size, how to, where to get. etc etc..Thanks
-- Edited by Peter and Jian on Sunday 29th of July 2018 02:56:42 PM
Hi Peter and Jian
I am uncertain about what you expect to hear about zenner diodes in this context ?? But lots of people have two batteries connected in parallel with no problems and not expecting any either.
You might have read something on the internet which has caused concern, however there is nothing to worry about. It you get a multimeter and learn how to use it a bit you can check your batteries every now and again by disconnecting one and seeing they are pretty equal. Generally if you start with two new equal batteries and connect then properly they will work together till they both die of old age together years later. Sometimes it may help to individually charge them each seperately to fully charged and then reconnect them but most do not do this. Nor do people use any zenner diodes in the system that I know about.
Jaahn
-- Edited by Jaahn on Sunday 29th of July 2018 06:02:48 PM
What would you expect a Zener diode to do? What have you been told?
Iza
The only reference I have encountered in automotive applications is where a high power zener is connected in parallel with a battery or alternator to protect sensitive electronic circuitry from voltage spikes. Such spikes occur during "load dump" events. A load dump is when the electrical load (eg battery) is abruptly disconnected while the alternator is delivering a high charging current.
I started to design and build such a set up before I discovered the advantages of lithium batteries that you could build from individual cell. The problem was then avoided all together so there was no need to continue with the build stage of the separate battery isolator set up. If drop in individual lithium 12v batteries were used even a circuit like this would not avoid one battery doing all the work till it died, but it would stop that battery from destroying the others in parallel.
T1 Terry
Hi dorian et al
Just for those interested in technical things. Bosch alternators for the last 20 years have their main power diodes as zeners. Probably other main brands also.
People may argue about this but it is a fact. So the zenner dioes do protect the vehicles electrical system from spikes etc which helps protect the electronics in modern cars. If you look carefully at the diagrams for the alternators you can see the difference in the symbols 
So if you want high powered zenners get them from alternators. Fixed voltages though !
Jaahn
No argument from me. Thanks for the info. (Didn't we discuss this before?)
http://www.bosch-motorsport.de/content/downloads/Products/resources/2778518027/en/pdf/Alternator_B3_Datasheet_51_en_2778485259.pdf
http://www.iskra-agv.cz/us/pdf/alternators.pdf
https://www.diodes.com/assets/Datasheets/BZV63_64.pdf