DC powered boards limited to 55v; how to handle on a 48v system (peaks at ~56.8v)?

I'm looking at a few pieces of DC powered equipment that don't like the high-end of a 16S 48v nominal battery ~57.6 volts). Examples include the Starlink POE injector (which cuts off if it sees 57v, even for a moment):


and a USB-C Power Delivery board that works in the 48v range but specifies 55v as DO NOT EXCEED max:


I already have the starlink PoE in my system, so I just adjusted all charging profile to max at 56v. Individual cells then max at 3.5 which is fine (perhaps sacrificing a little capacity, although I think I have a runner or two that cause OVP when charging to 3.65 anyway). This is working fine.


But the 55v is starting to get fairly low.

So a general question: is a DC-DC charger the only option here? But those seem either expensive or only work at low amps. I don't need variable output/variable input, so I wonder if there is an electrical solution that "caps" voltage above a certain level? This would be "per-device", so pretty low amps (like 1.5A).

I convert my "48V" battery to 12V for various 12V things I need like router, mini-PC, etc.


Then I convert my 12V back to direct 48V to run my starlink POE.


Efficiency probably is lossy, but I expect it's less than 25W as my DC loads are about 150W typically.

With these in place, I can adjust my charge voltage willy-nilly.

My battery has comms that set the charge voltage to 55v. Not much power above that.

jameshowison said:

general question: is a DC-DC charger the only option here? But those seem either expensive or only work at low amps.

Click to expand...

You haven’t listed a use case that stresses a DC DC converter much in terms of power not expense.

And what you are asking for is basically a DC DC buck converter.

You can probably find 60V tolerant DC buck converters on Amazon (though you’d probably want to buy from a better source).

Limit your 16S LFP to 55V or 3.43V per cell voltage. You will need BMS that allows to set custom cell balancing voltage. You battery will still charge to 95% or above. Another benefit is longer battery life.

Just put a couple of diodes in series with what you want to power. Diode bridge blocks would be easy to mount. Just connect battery POS to the NEG terminal of diode. The POS of diode goes to whatever you want to power. Each bridge will reduce the voltage about 1.5V. Two in series would drop 3V. This would be very consistent in regards to current draw. Solder or use spade connectors.