Can alternator be connected directly to DC-DC charger?

[User 09]

I dont fully understand the full capabilities of DC-DC chargers. In another users post I was interested in, the question came up in my mind. Out of curiosity I was wondering...

If you had a lead acid start battery and a lithium house bank with an unregulated (dumb) alternator, could you put the alternator output wire, the lead acid start battery positive wire and the DC-DC charger input wire all on a single busbar that would then allow the alternator to charge the lead acid start battery and the lithium house bank at the same time while the engine was running? I guess effectively sending any alternator output current directly through the DC-DC charger.

My thinking for doing it this way was that IF there was a problem with the lead acid battery and you had to motor for a long while before you could get to a place where you could replace the lead acid battery, that the lead acid battery could be disconnected, you could motor with the engine with the DC-DC charger turned on, the alternator could charge the liyhium house bank safely without burning up the alternator.

Does this make sense?

[smac999]

the alternator charges one battery. a dc to dc goes from a battery to a battery.

where you make those connections doesn't matter as long as the wire size is correct to do what you want.


you can't disconect the lead battery. the dc to dc needs a battery to buffer the surge start up currents.

[cram]

Originally Posted by User 09

I dont fully understand the full capabilities of DC-DC chargers. In another users post I was interested in, the question came up in my mind. Out of curiosity I was wondering...

If you had a lead acid start battery and a lithium house bank with an unregulated (dumb) alternator, could you put the alternator output wire, the lead acid start battery positive wire and the DC-DC charger input wire all on a single busbar that would then allow the alternator to charge the lead acid start battery and the lithium house bank at the same time while the engine was running? I guess effectively sending any alternator output current directly through the DC-DC charger.

of course! Pacific yacht systems has many diagrams showing this


https://www.pysystems.ca/resources/diagrams/

My thinking for doing it this way was that IF there was a problem with the lead acid battery and you had to motor for a long while before you could get to a place where you could replace the lead acid battery, that the lead acid battery could be disconnected, you could motor with the engine with the DC-DC charger turned on, the alternator could charge the liyhium house bank safely without burning up the alternator.

Does this make sense?

that will not work. The alternator must have a battery connected to it. It will not work with just a dc dc converter as it needs the capacity of the battery to help regulated current and voltage but also to provide power to the alternator field.

[TheShanghaiist]

Hi, the alternator wasn’t designed to handle the way a DC-DC charger draws current, which can lead to overheating or even alternator failure over time.
By connecting the DC-DC charger to the motor battery, the battery acts as a buffer, ensuring smoother current flow and protecting your alternator from damage.
Also, it’s a good idea to choose a DC-DC charger with a +in signal feature, so it only turns on when the alternator is running. This helps avoid unnecessary load on your system and ensures everything operates as it should. Cheers, Antoine

[User 09]

Thanks for replies. yeah i was thinking without the battery as a buffer but learned after some more research this is not possible. Appreciate the feedback.