48V to 12/48V charging?

[nfbr]

Originally Posted by RaymondR

If your 48 volt battery is made from 4 each 12 volt batteries in series you could just tap off 12 volts for light or short term loads like anchor winches.

No. Absolutlely No.
This will unbalance the pack and destroy it rapidly. Some batteries will heavily overcharge whilst others are undercharged. Or some will go far lower than others.

Don't do this.

[s/v Jedi]

Originally Posted by RaymondR

If your 48 volt battery is made from 4 each 12 volt batteries in series you could just tap off 12 volts for light or short term loads like anchor winches.

This is okay for emergencies, but it will unbalance the battery bank so not recommended for general use.

[Lepke]

Originally Posted by RaymondR

If your 48 volt battery is made from 4 each 12 volt batteries in series you could just tap off 12 volts for light or short term loads like anchor winches.

I had a commercial fishing boat the PO had setup with a 32v system using 2-12v and 1-8v 8d batteries. One of the 12v was tapped. It lasted less than a year. It's replacement lasted less than a year. I quit tapping the 12v.

[RaymondR]

Originally Posted by Lepke

I had a commercial fishing boat the PO had setup with a 32v system using 2-12v and 1-8v 8d batteries. One of the 12v was tapped. It lasted less than a year. It's replacement lasted less than a year. I quit tapping the 12v.

Yep, that will happen if you draw down one cell excessively too regularly which is why I specified light or intermittent loads. A possible solution might be to parallel the tapped cell so that it does not get cycled so severely.

[PaulCrawhorn]

Just to clarify and reinforce the point above.

There is a 12V system circuit, and another at 48V.

Both have battery banks sufficiently large (Ah) for however many days overall usage, and

powerful enough (peak vs continuous Amps current) to drive the thirstiest loads.

The MPPT or DC-DC used to convert from 48V to 12V is charging the 12V bank for hours per day (many if it is lead)

not feeding the larger 12V loads directly.

There are DCDC converters that "can handle" big kWs but reliable ones are very very expensive and require specialist skills and experience that is very rare and hard to find.

[mcarthur]

Originally Posted by s/v Jedi

The mppt only has to provide average power draw (close to zero for windlass battery) because the fully charged battery provides the power for the windlass.

Ah true. I was trying to get away from having a 12v battery at all (perhaps apart from starting). It would be best if all the 12v loads could be done through a 48-12 buck converter instantaneously, doing away with a(nother) heavy battery.
For windlass, put a dedicated converter next to the windlass and you can make do with much smaller wiring for the (possibly) long run as it's at 48v.

[GrowleyMonster]

Originally Posted by aybabtme

With 48V propulsion banks becoming more common, and with the assumption that the 48V bank would come with a 12V circuit for legacy loads, and that the 48V bank is much larger and thus receives the charge of all power sources... where are the 48V to 12V battery-to-battery chargers?

Here's the layout I have in mind:

• a large 48V LFP propulsion battery
  • solar/mppt charger
  • hydrogen charger
  • inverter/charger
  • directly powers compatible 48V high DC loads (not many yet)
• a small 12V starter battery (to power high amp loads like windlass)
  • kept charged up from 48V bank
  • runs lights, LEDs (small load)
  • runs electronics (small load)
  • runs windlass, winches (high load, requires starter battery)

Similarly, if I have a large propulsion bank on my boat and a smaller one for the electric outboard on my dinghy. Need a 48V to 48V battery charger. Where are they?

It seems like the big manufacturers all have a 48V blind spot.

When I had my 48v boat I used cheap DC/DC converters, easily replaced. I also had a bilge pump tapped into the bank at 12V, At first I used a separate 12V battery but later I got rid of it and ran everything off the propulsion bank and DC/DC converters as needed. Be sure to properly fuse everything! Also the cheap DC/DC converters on fleabay should be downrated about 50%. Don't ask me how I know. So get one rated for twice the current you think you will draw for that circuit. You can connect several converters to your 48V to separately power more than one 12v circuit. Since they are cheap, keep a couple of spares.

As EP gets more popular, 48V systems will be in enough demand that manufacturers will take an interest. As it is, 48V equipment is a pretty small niche market. Look to golf cart stuff for a lot of gear, especially lighting.

[GrowleyMonster]

Oh and for the windlass, I would SERIOUSLY look into replacing the motor with a 48v motor. Same with bow thruster if you have one and the motor is not severely integrated into the thruster where you can't really swap it.

[aybabtme]

I know Sailing Uma (youtubers) did this conversion of 12-to-48V windlass stuff but they also had issues with corrosion and walked back from this once they could find a proper 48V model.

[s/v Jedi]

Originally Posted by aybabtme

I know Sailing Uma (youtubers) did this conversion of 12-to-48V windlass stuff but they also had issues with corrosion and walked back from this once they could find a proper 48V model.

I bought a new Maxwell motor for my Maxwell windlass (went from 12V to 24V). You may be able to just buy a 48V motor but you can also have the current 12V motor rewound for 48V.

[mcarthur]

I believe Maxwell introduced new 48V windlasses* this year.


*windlassii? windlassi? windli? Ahh English!