Charging multiple banks from a charge controller and charging between banks

[Jagarwal]

Hello fellow cruisers

I am designing the charging system surrounding my upcoming conversion to EP. I have included a simplified diagram of the system.

My design requires a few things to work that I am not certain will; thus I seek advice from more experienced system designers and solar installers.

The system will have two 48V banks, one in each hull, to power said hulls respective pod-motor. There is also a 24V house bank in the bridge-deck that is already in place and operating satisfactorily. I intend to redirect all solar charging to the 48V banks to take advantage of the larger arrays each charge controller would be able to handle. The pod motors will be able to charge their respective bank with hydrogeneration when the boat is sailing.
The 24V house bank would be kept topped up by the 48V banks.

First question: Can I use a solar charge controller to safely charge the 24v bank from the 48V batteries? It seems like it would work but I would like to hear of anyone successfully doing this in their own installation.

Can I use a 0 1 2 switch to effectively select which, or neither, of the 48V batteries the mppt controllers are seeing? The charge profile would be the same for both banks. This is necessary so that I can direct all charging to one bank or the other if one or the other is full or they are out of balance.

Any advice welcome thanks!

[AnsleyS]

Jagar,


It may be easier to use a dc/dc converter such as this:


ORI482441110 Orion-Tr 48/24-16A (380W) Isolated DC-DC converter


and use the switch for the input.

[Jagarwal]

Thanks for your reply Ansley,

I think you may be right that such a converter is the best option. I was hoping I could simplify the components required, in case a unit fails I can grab one from elsewhere, while also getting a little more bang for the buck. But unless someone pipes up reporting successfully using a charge controller like this, I will follow your advice.

When you say use the switch for the input you refer to selecting the bank to be charged? I do hope this is possible with such a simple approach.

Jack

[BjarneK]

If the 48 V batteries and the 24 V battery have a shared ground, it is not a good idea to use Victron MPPTs to charge the 24 V battery from a 48 V battery. The problem is that it becomes impossible for the MPPT to measure (and control) its output current since there are several paths to ground. See here for an explanation regarding a slightly different scenario with the same problem: https://www.cruisersforum.com/forums...ml#post3595300

If the grounds are not connected, it is possible to use Victron MPPTs to charge the 24 V battery from the 48 V batteries. In this case the ground would in fact get connected through the (non-isolated) MPPT. It is important to make sure there are no other connections between the grounds for the different batteries. I think it would be difficult and impractical to have completely separate grounds for the different batteries.

So I agree that a DC/DC converter is the best option for charging the 24 V battery.

[Jagarwal]

Originally Posted by BjarneK

If the 48 V batteries and the 24 V battery have a shared ground, it is not a good idea to use Victron MPPTs to charge the 24 V battery from a 48 V battery. The problem is that it becomes impossible for the MPPT to measure (and control) its output current since there are several paths to ground. See here for an explanation regarding a slightly different scenario with the same problem: https://www.cruisersforum.com/forums...ml#post3595300

If the grounds are not connected, it is possible to use Victron MPPTs to charge the 24 V battery from the 48 V batteries. In this case the ground would in fact get connected through the (non-isolated) MPPT. It is important to make sure there are no other connections between the grounds for the different batteries. I think it would be difficult and impractical to have completely separate grounds for the different batteries.

So I agree that a DC/DC converter is the best option for charging the 24 V battery.

Thanks BjarneK for the link and insight into the behavior of the MPPTs. I am updating my diagram to plan for the DC-DC chargers