48V to 12/48V charging?

[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.

[s/v Jedi]

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.

I think you may be able to use a solar controller as 48V to 12V battery charger…

[KTP]

When we converted our 34 foot Pacific Seacraft to electric and a 48V system, I purchased a high end DC-DC (sealed, big aluminum finned heat sink, no fan needed) that provides 50 amps (made by CUI) which we use to run all of the 12V stuff...but we don't have electric winches or anything that would draw the type of power you need.

I like not having to have a 12V bank and the DC-DC is something like 92% efficient.

[PippaB]

Originally Posted by s/v Jedi

I think you may be able to use a solar controller as 48V to 12V battery charger…

+1. Built in charging algorithms. Not an absolute necessity, but I prefer those capable of having the MPP tracking turned off, use a constant input voltage, and then if you have a small battery on the other side you can them to constant float.

[Jammer]

Victron has 48v to 12v dc chargers in various ratings at reasonable prices.

[mcarthur]

Originally Posted by s/v Jedi

I think you may be able to use a solar controller as 48V to 12V battery charger…

Yep, or choose a buck converter. If you have a mix of charging between 48v and 12v, like solar and alternator, you could use a bi-directional buck-boost like the Calex 3000 which will give quite a lot of power to the 12v for loads like bilge pumps, water pumps and biiig loads like windlass and winches.

[seandepagnier]

Originally Posted by s/v Jedi

I think you may be able to use a solar controller as 48V to 12V battery charger…

-1

This could burn out the controller, or at least probably not do what you want. It expects a current source like a solar panel, not a voltage source like a battery. So it will draw more and more current from the battery until it hit the limit of the controller and who knows how it reacts since normally solar panels attached should not be powerful enough to do this.

You just want constant current constant voltage dc-dc converter. You still need a small 12v battery to have a reasonable system in most cases. This could even be a 20 amp hour lithium battery or something like that. Dont use a "starter" battery... can you run the windlass on 48v?

I got a CC/CV dc-dc converter for $15 aliexpress. It claims 150 watts but I run it around 60 watts. You set both voltage output (in my case 14 volts) and current I use 5 amps) using screws.

Now, I left it plugged in to the 12v battery but not the 48v one. Then solar into the 12v one exceeded the 14v setting and somehow this converter acted as a shunt (strange) and got very hot absorbing the excess solar power. It blew the capacitors. I replaced the capacitors and the converter works as expected again. Just be aware of this, and maybe use a blocking diode to prevent power flowing from the 12v into the converter if you get the cheap converters

For 48v to 48v you can simply connect the two batteries using long enough thin wire (to limit current) as a simple solution but this has some limitations. A better way is to charge the 48v battery from solar rather than the other battery if possible. For dc-dc boosters typically have an issue here as the voltage differential could be too small you may need a buck-boost with CV/CC setting to get a faster charge and to charge one battery higher than the other.

[s/v Jedi]

Originally Posted by seandepagnier

-1

This could burn out the controller, or at least probably not do what you want. It expects a current source like a solar panel, not a voltage source like a battery. So it will draw more and more current from the battery until it hit the limit of the controller and who knows how it reacts since normally solar panels attached should not be powerful enough to do this.

There is no difference. The controller can not pull the input voltage down so yes, current ramps up to what the controller can handle. A DC-DC charger gives equal result. Also, the MPPT controller won’t burn up.

The thing is that the whole MPPT algorithm is useless because input voltage doesn’t change and so the maximum power transfer is always at input voltage and max. current the controller can handle for that voltage. This is exactly what a dc-dc charger without MPPT algo does, so you’re paying for something you don’t use… but it works :-)

[redneckrob]

Originally Posted by s/v Jedi

There is no difference. The controller can not pull the input voltage down so yes, current ramps up to what the controller can handle. A DC-DC charger gives equal result. Also, the MPPT controller won’t burn up.

The thing is that the whole MPPT algorithm is useless because input voltage doesn’t change and so the maximum power transfer is always at input voltage and max. current the controller can handle for that voltage. This is exactly what a dc-dc charger without MPPT algo does, so you’re paying for something you don’t use… but it works :-)

I agree. If they burned up or behaved unexpectedly when driven at their rated power then they would be burning up any time someone put solar on at the rated amount since also will hit the rated amount for potentially several hours a day. In reality I seldom hear of folks having any problems with them.

[s/v Jedi]

Originally Posted by redneckrob

I agree. If they burned up or behaved unexpectedly when driven at their rated power then they would be burning up any time someone put solar on at the rated amount since also will hit the rated amount for potentially several hours a day. In reality I seldom hear of folks having any problems with them.

I’m sure there’s hardware out there that can burn up, but I know for sure Victron SmartMPPT controllers will do this, because I test them with a big power supply at 30V instead of solar panels
They limit power when they get too hot.

[PaulCrawhorn]

Some solar controllers cannot work as DCDC converters from other source types.

Victrons are widely known to be fine for that

[aybabtme]

Originally Posted by Jammer

Victron has 48v to 12v dc chargers in various ratings at reasonable prices.

They don't have the chargers in that range, just the converters.

[aybabtme]

My understanding is that the MPPT (Victron included) can/keep themselves the right to short the inputs under certain conditions, which is fine for solar panels (disables them) but obviously not for a battery. This is why I'm concerned about using them, otherwise I would.

With regard to 48V-48V with a long thin wire, this won't work for a permanent install for safety reasons, and if different chemistries are used. A CC-CV buck-boost converter is what I'd want at a minimum, and really something with a charge profile on the output would be best.

[s/v Jedi]

Originally Posted by aybabtme

My understanding is that the MPPT (Victron included) can/keep themselves the right to short the inputs under certain conditions, which is fine for solar panels (disables them) but obviously not for a battery. This is why I'm concerned about using them, otherwise I would.

This isn’t a concern because the controller will only get a low input impedance when the connected source can’t deliver enough current to transfer the power needed for maximum charge output.

They should have been the Smart isolated units so that you get correct charge profiles.

A tip for those who worry about keeping batteries or cells in balance: a Victron Smart BMV allows midpoint monitoring, explained for two 12 V batteries, but you can also have (example) four lfp cells on each side. Even though it doesn’t report balance levels for individual cells, you do get an overall idea of balance in the battery bank and you can set alarms as well.

[RaymondR]

A solar controller does not know what sort of DC electricity it is being fed or where it comes from. As long as the voltage imposed upon the controller is withing the voltage range limits it is designed for it will not be harmed.