question

ningaloo avatar image

Charging 12V AGM from 48V lithium

I am commissioning a new boat which will have 3 x 160Ah AGM batteries for the 12V house bank. I have a 310W solar panel and propose using a SmartSolar MPPT 100/30 for this. I also have a "spare" 1200Wh 48V lithium battery and I'm wondering if I could use this as an alternative source for topping up the 12V system through the same solar regulator (having a switch to ensure only one source at a time). I would only plan to use this when sailing at night when my solar contributes nothing and I'm using a fair bit of power with fridge, instruments, lights and autopilot.

For the sake of this scenario I am not worried about getting the 48V battery recharged - that is another issue.

Any drawbacks in this arrangement?

battery chargingmppt smart solar
2 |3000 characters needed characters left characters exceeded

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

2 Answers
ningaloo avatar image
ningaloo answered ·

So I have done some more reading up on the potential issues using the mppt regulator for dc-dc charging. I understand that there is a possibility of the regular shorting the input(?) to protect the battery from overcharging. This may be ok when using PV but not a battery as input.

I cannot find any 48-12 chargers but there are 48-12 Orion converters which seem to be recommended for my scenario.

So my follow up question is how this might be configured. If I got the 9A converter this would meet my needs. Does the device limit the current to 9A from the 48V input? I'm thinking I would set the charging voltage to be 13.8(?) for the AGM and manually switch off when/if the SOC reaches a predetermined level.

Does this sound right?

2 |3000 characters needed characters left characters exceeded

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

dazey77 avatar image
dazey77 answered ·

Why would you not use an Orion DC-DC converter for this? e.g. Orion-Tr 48/12-9

1 comment
2 |3000 characters needed characters left characters exceeded

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

I have looked at these however I thought that these were "just" voltage converters. Do they also take the SOC of the 12V into account and have multi- levels of charge based in this?