looking for DC2DC charger 12V to 24V 60 or 80A not Victron

[s/v Jedi]

Originally Posted by CaptainRivet

Hi jedi,
well my system is not the problem, designed to run at 600A constant with 12V so have enough headroom in 24V now

the issue here is they are 2 types of converter around, not one:
type 1: the converter type which simply converts the volts up or down and the curcuit is designed for x amps=load max., when you exxceed the amps the device fuse blows or it simply burns through. Cannot use as charger.

type 2: charger or power supply type which converts an amount of voltage and amps, protected by a current limiter designed to run x amount when hot and overtemp protection. exactly as you describes it starts cold and will do 30A, then as it gets hot it will throttle the output to control it’s temperature.
So if you hook type 1 to an LFP with an internal resistance of 10-20mOhm, so basically a short, the voltage regulation will go bonkers and because nothing limits the current the device fuse will blow. And looking at the price and cannot find another thread where these Orions are used as charger make me think its a type 1. I can find plenty for the 24/12 70 and all are type 1 scenarios, no single one charging an LFP.

Will get 2 of the Orion 24-12-70A (70A ones) to convert down from 24V for the legacy nav station and new 12V loads. COuld test with one but will post in Victron forum and ask there about LFP charging.

No, there isn’t a converter that will blow up. I can imagine it do this when you short the output terminals, not when you connect a 24V battery. If this ever happened to someone then the battery must have been showing no output voltage, shorted internally etc. More probable is that they did a faulty installation.

By the way, I am a retired electronics designer and did design power supplies, chargers and converters.

[CaptainRivet]

Originally Posted by s/v Jedi

No, there isn’t a converter that will blow up. I can imagine it do this when you short the output terminals, not when you connect a 24V battery. If this ever happened to someone then the battery must have been showing no output voltage, shorted internally etc. More probable is that they did a faulty installation.

By the way, I am a retired electronics designer and did design power supplies, chargers and converters.

Well you basically short out the terminals when connecting a 24V LFP. it has 10-20milli ohm resistance. Its the resistance of the cabling,busbars and fuses that actually the converter sees.

[s/v Jedi]

Originally Posted by CaptainRivet

Well you basically short out the terminals when connecting a 24V LFP. it has 10-20milli ohm resistance. Its the resistance of the cabling,busbars and fuses that actually the converter sees.

No, a 24V LFP battery has a significant voltage level, above 24V unlike a dead short.

Consider this: when the battery would be 26.3V and you set the converter to 26.2V, then this doesn’t change the battery internal resistance, right? But still there will be no output current from the converter… in fact, the battery will try to charge the converter because it has a higher potential.

The absolute maximum of this converter is listed at 30A so for your way of reasoning, consider it a converter that limits output current to 30A and is de-rated to much less current when it heats up.
In an ambient temperature of 25 Celsius it will only be able to do 20A after being switched on for a while. In 30 Celsius even less.

This is how maximum output vs continuous output works. The thing with Victron is that there is a larger difference between the two because of their design filosofie. They put in components that can do 30A instead of 20A and rely on minimum cooling or even completely passive cooling while still meeting their continuous output rating. This means you must have circuits for more than it’s maximum rating and that includes breakers or fuses because if you don’t, they will trip.

For rule of thumb, take maximum output times 1.5 and have wiring and breakers for that value. So with a rating of 30A max, your circuits should be designed for 45A and this is the breaker/fuse value. For the wire, a marine grade conductor can do 45A at AWG 12 but this means the wire will run hot at 100 degrees Celsius which isn’t cool So you go higher. Let’s say you double it for finding a compatible ampacity so that is 90A. Now you are in between AWG 8 at 80A and AWG 6 at 120A. You can choose either one of those because you have taken more than enough safety margins. Let the choice be the distance of the circuit and calculate the voltage drop at 30A and see if that is acceptable with AWG 8.

[CaptainRivet]

Originally Posted by s/v Jedi

No, a 24V LFP battery has a significant voltage level, above 24V unlike a dead short.

Consider this: when the battery would be 26.3V and you set the converter to 26.2V, then this doesn’t change the battery internal resistance, right? But still there will be no output current from the converter… in fact, the battery will try to charge the converter because it has a higher potential.

The absolute maximum of this converter is listed at 30A so for your way of reasoning, consider it a converter that limits output current to 30A and is de-rated to much less current when it heats up.
In an ambient temperature of 25 Celsius it will only be able to do 20A after being switched on for a while. In 30 Celsius even less.

This is how maximum output vs continuous output works. The thing with Victron is that there is a larger difference between the two because of their design filosofie. They put in components that can do 30A instead of 20A and rely on minimum cooling or even completely passive cooling while still meeting their continuous output rating. This means you must have circuits for more than it’s maximum rating and that includes breakers or fuses because if you don’t, they will trip.

For rule of thumb, take maximum output times 1.5 and have wiring and breakers for that value. So with a rating of 30A max, your circuits should be designed for 45A and this is the breaker/fuse value. For the wire, a marine grade conductor can do 45A at AWG 12 but this means the wire will run hot at 100 degrees Celsius which isn’t cool So you go higher. Let’s say you double it for finding a compatible ampacity so that is 90A. Now you are in between AWG 8 at 80A and AWG 6 at 120A. You can choose either one of those because you have taken more than enough safety margins. Let the choice be the distance of the circuit and calculate the voltage drop at 30A and see if that is acceptable with AWG 8.

Thank you Jedi for explaining. Input wire is about 2m each, output 30cm to charge busbar. Calculate with factor 2 but I Always use/upgrade to max wiring size that fits in connector of device to reduce voltage drop. in this case 2 Victron Orion Smart 12/12 30A will be replaced by 2 Orion 12-24V 40A/20A. input +35sqmm or AWG 2 which is already installed and output changed from 16sqmm to 35 or AWG 2, minus changed from 2x16sqmm to 70sqmm or AWG 2/0 as it’s one wire in/out. MegaFuse 80A in and NH00 63A out.

[CaptainRivet]

Whole Installation is kept in AWG 6,2 and 2/0, if I need 300A I use 2x2/0 as also easier to route.
Like this limited wire sizes as spare and needed tools are limited and cheaper too, Eg hydraulic wire crimper goes 10-till 2/o, next size up is triple the costs.