???Multiple sources of DC voltage being fed to battery bank???

[RaymondR]

Originally Posted by CassidyNZ

But if an alternator is left switched on (energised) it will certainly drain a battery.

I have three alternators, one is the standard alt fitted to the Yanmar and switched on/off with the ignition key, the other two are big-frame alts mounted about-face on a seperate bracket, driven by the crank pulley and the fields are independently switched from the main electrical DB. This way I can run the alternators that I need/want by switching the fields on or off.

But if I stop the engine and leave the fields on the two big-frame alts switched on (something that I have accidentally done more than once ), each alt will continue to draw about 4.5A until the batteries are flat. The key give-away is that hours after the engine is stopped, the alternators will still be warm.

The magnetic field required in order for the alternator to produce current is created by flowing a current through the rotor coil. This excitation current is initially provided to the regulator via the ignition circuit. When the alternator starts producing current it takes over the provision of the excitation current. When you shut the engine down this charge is no longer available and if you leave the ignition key on the regulator will take current from the battery and eventually flatten it. If this is a common problem you can take a tap off the oil warning light to a relay to open the tap from the ignition circuit and prevent flattening of the battery.

[smac999]

What do you think a battery bank is? It’s multiple sources of dc all feeding each other..,, Since the batteries are all same voltage. nothing bad happens.

Same with chargers.

[YANDINA]

Originally Posted by RaymondR

You can have as many charging sources as you like however each one of them must have a blocking diode to ensure that the current can only flow one way otherwise they will short out and flatten the batteries when they are not charging them.

No need for blocking diodes, they are already inherent in charging sources. Batteries do not "flatten batteries when they are not charging" otherwise you would have to disconnect the charger battery leads any time you turned it off.

Charging sources don't "Know" if other sources are charging, all they can see is a destination voltage so they provide charge appropriate for that voltage.
They may not share the charging function equally since they will not have matching profiles, but all will contribute charge so long as the charge level has not reached the top limit.

[RaymondR]

Originally Posted by YANDINA

No need for blocking diodes, they are already inherent in charging sources. Batteries do not "flatten batteries when they are not charging" otherwise you would have to disconnect the charger battery leads any time you turned it off.

Charging sources don't "Know" if other sources are charging, all they can see is a destination voltage so they provide charge appropriate for that voltage.
They may not share the charging function equally since they will not have matching profiles, but all will contribute charge so long as the charge level has not reached the top limit.

I did not carry out a review to ensure that all regularly utilized charging sources have blocking diodes having assumed that all modern charge sources contain electronics and most probably diodes somewhere in the DC part of the circuit. However when DC generators were common it was not the case.

Batteries have not generally been considered charge sources although this is changing.

[LoudMusic]

Originally Posted by smac999

What do you think a battery bank is? It’s multiple sources of dc all feeding each other..,, Since the batteries are all same voltage. nothing bad happens.

Same with chargers.

Batteries are sources and loads, depending on the voltage on the line.

[PaulCrawhorn]

No need to woory about this at all, not an issue

Just ensure each source is in the ballpark for what the battery is specked for, and they can all turn off and on as they like, no diodes, no master "controller" is required, there is nothing to the myth about them "fighting each other", everything works out just fine.

[YANDINA]

Originally Posted by RaymondR

I did not carry out a review to ensure that all regularly utilized charging sources have blocking diodes having assumed that all modern charge sources contain electronics and most probably diodes somewhere in the DC part of the circuit. However when DC generators were common it was not the case.

Batteries have not generally been considered charge sources although this is changing.

Modern alternators generate AC voltage that is rectified to DC using diodes so no protection needed.

When DC generators were common (75+ years ago I estimate), they still had to have isolation of some sort otherwise they would start to draw current back out of the battery and run like a motor when the engine was turned off. It was probably a centrifugal switch on the shaft?.

[RaymondR]

Originally Posted by YANDINA

Modern alternators generate AC voltage that is rectified to DC using diodes so no protection needed.

When DC generators were common (75+ years ago I estimate), they still had to have isolation of some sort otherwise they would start to draw current back out of the battery and run like a motor when the engine was turned off. It was probably a centrifugal switch on the shaft?.

They generally just relied on you turning the ignition off, a lot of vehicles did not have a key, just a big switch on the dash and a separate starter button.