DBC-1212 battery thingy...what is it?

[jonrarit]

Ok just spent my first week aboard my new (to me) 2005 Bavaria 36 cruiser and discovered a unit mounted under the chart table that I am trying to identify what it is and what it does.

Picture attached and I'm open to ideas as googling is revealing very little for once

Thanks

Jonathan

[Yngmar]

Same as this, a DC-DC charger for an emergency battery required for charter coding.

[Symphony]

That is better than the one often fitted. You will find your VHF connected to its own battery which is charged from the house battery through that device. You can either leave it or disconnect it all and use the battery space for larger house batteries. The VHF then needs to be powered from the panel.

[jonrarit]

Brilliant guys many thanks.

There are three batteries on board two large 140ah and a smaller one (cant remember the rating) I assumed the two big ones were the same and both domestic and the smaller battery was the starter however from what you're saying it would appear the two large ones are one starter, one domestic and the small battery is in fact the emergency VHF one.

Will check when I am next out there

thanks

jonathan

[B40-Lefkas]

Having made a similar post myself, I can respond. I would think that you were right in the first place about the batteries - the 140ah ones are house batteries and the smaller the engines start. On my boat there were an additional TWO 44 ah batteries for the TWO VHF radios (yes, ex-charter in Greece). The DC-DC charger fed those VHF batteries. I would guess that the VHF batteries have already been removed from your boat, but it's also possible that the 1212 is feeding the starter battery.

BTW I removed the two VHF batteries and added another 185 ah house battery in it's place, doing away with the DC-Dc charger setup.

[Nigel]

I've often wondered about fitting a small SLA battery to power the VHF. What capacity is normal?

[Lyra]

There are  units of 7Ah popular in portable amplifiers, alarm systems etc.
Assuming a  typical VHF unit consumes an average of ~0.5A this can provide several hours of operation.

[landes_h]

A mounted VHF-FM marine radio (25W) draws minimum 5 Amps in transmit mode. If your boat is about to sink and you make an emergency call it's a simple calculation of how big the battery must be, to transmit your MAY-DAY until the boat is under water.     

[Nigel]

I would have expected a current draw of about 3A on TX, but even so a 7Ah seems adequate. Has anyone got a schematic diagram of a suitable B2B charger?

[Lyra]

As far as I remember. although physically large, the B2B charger that I have (same as in the photo) is very light and I think most of the volume goes for the displays, connectors etc.
I might be at the boat this week and be able to take a look what is inside, but it should be a simple DC-DC converter that would be able to work with a say 10-15V input and output the floating voltage for the SLA (I think it is 14.1V for the 7Ah gel type SLA).
There is no need for "smart" charging because normally the battery remains fully charged (or hardly depleted) so setting it once to floating voltage should be sufficient. Deep discharge will occur only in the rare emergency situation for which it is intended.

[Lyra]

opened up the unit ant took a look.
It is actually not only a charger but a charger-changer.
It seems that what is is doing is as follows:
While the main battery is OK it charges the emergency battery and also drives the load.
When the main battery is not present it connects the emergency battery to the load
everything is totally analog - two ICs, several transistors, passive components and a relay (and as already seen the displays are analog).