Dc step up

[Jake8]

Hi Forum,

I am looking for a powerfull (+/-1800watt) dc step up converter to get 14VDC to 75VDC ~5Amps

Can someone help me out with a good product?

 

[KlausST]

Hi,

You are looking for a schematic? a ready to buy module? A complete power supply including enclosure? Industrial or some bench top device?

What does this "+/-" mean at the WATTs?

Why do you say 1800W, while 5A at the max output voltage of 75V, just gives 375W?

Klaus

 

[Jake8]

Hi,

You are looking for a schematic? a ready to buy module? A complete power supply including enclosure? Industrial or some bench top device?

What does this "+/-" mean at the WATTs?

Why do you say 1800W, while 5A at the max output voltage of 75V, just gives 375W?

Klaus

I am looking for a ready to buy module

+/- becouse it would be nice to fine tune it

1800watts to let the mosfets breathe a little, becouse the "standard" products have the mosfets rated at only 15amps. But see it more as a preference instead of a requirement.

 

[KlausST]

Hi,

I don´t get it.
You want to "fine tune" the 1800W on a ready to buy module wher you draw max. 375W from.

How do you think this works? What is your idea?

And with SMPS the "output current limiting" factor usually is the inductance with it´s core getting into saturation.

****
"Step up" always means SMPS
... but your 1800W MOSFET thing more sounds as if you think about the power dissipation of an analog supply.

Klaus

 

[Jake8]

Thanks for your reply

I read a little confusion so let me try to clear this out by a short background story (please don't mind my english becouse i am dutch)

A Friend of mine gave me a 3000watt 230VAC (Growatt SPF3000) island inverter with a lion 4kwh battery. I mounted this set into my rv.
This inverter has 2 mppt inputs. To one of these inputs i connected 4pc 420wp solar panels
and on the other input i try to connect the rv's alternator who can supply 14VDC/120A so that the battery charges whils driving even if there is no sunlight.

The mppt requires a 75voc to start (datasheet says 65v but i think that is 65vcc) Now i am trying to boost up the 14vdc alternator voltage to 75vdc in order to feed the mppt with 5amps/375watt, this will draw 30amps at the dc step up IN. Offcourse i dont want to blow up the dc step up's capacitors due to time constant mppt v/s capacitors and also the mosfets becouse of the high current draw.

But maybe i see it wrong and there is a better solution. I was thinking about 2 dc step ups wired parallel to curb the currents.

 

[Jake8]

A Friend of mine gave me a 3000watt 230VAC (Growatt SPF3000) island inverter with a lion 4kwh battery. I mounted this set into my rv.
This inverter has 2 mppt inputs. To one of these inputs i connected 4pc 420wp solar panels
and on the other input i try to connect the rv's alternator who can supply 14VDC/120A so that the battery charges whils driving even if there is no sunlight.

The mppt requires a 75voc to start (datasheet says 65v but i think that is 65vcc) Now i am trying to boost up the 14vdc alternator voltage to 75vdc in order to feed the mppt with 5amps/375watt, this will draw 30amps at the dc step up IN. Offcourse i dont want to blow up the dc step up's capacitors due to time constant mppt v/s capacitors and also the mosfets becouse of the high current draw.

But maybe i see it wrong and there is a better solution. I was thinking about 2 dc step ups wired parallel to curb the currents.

 

[KlausST]

Hi,

I'm not shure it works like expected.

2 things worry me:
1) MPPT on a 75V constant voltage source coming from the step up. MPPT tries to increase current ... and for now it's not clear why it should be limited to 5A. Usually a solar panel does not as a constant voltage source, but more like a constant current source. And thus the MPPT expects this behaviour.

2) Paralleling two SMPS is not a simple task. Each one tries to regulate a dedicated output voltage ... and you usually can't adjust both SMPS for reliable equal power sharing ... unless they are designed for this.

For a further discussion I recommend to draw a sketch about the devices and their wiring.

Klaus

 

[mtwieg]

In principle, using a DC supply as an input to a MPPT controller can work, but it whether it actually will work will depend on how your inverter implements the MPPT. It might be worth it to first try connecting a simple 75V supply to the inverter before trying for anything more complicated.

Most off the shelf DCDC converters will be limited to 48V or less. Your best bet may be to use two isolated converters each with output voltages around 36V, and put their outputs in series to get ~72V total. For example two of these modules: https://www.digikey.com/en/products/detail/cui-inc/VHK200W-Q24-S48/1992350

 

[Jake8]

Hi,

I'm not shure it works like expected.

2 things worry me:
1) MPPT on a 75V constant voltage source coming from the step up. MPPT tries to increase current ... and for now it's not clear why it should be limited to 5A. Usually a solar panel does not as a constant voltage source, but more like a constant current source. And thus the MPPT expects this behaviour.

2) Paralleling two SMPS is not a simple task. Each one tries to regulate a dedicated output voltage ... and you usually can't adjust both SMPS for reliable equal power sharing ... unless they are designed for this.

For a further discussion I recommend to draw a sketch about the devices and their wiring.

Klaus

Hi,

The rv alternator Imax is 120A, a 5A limitation on the SMPS OUT will draw 30A on SMPS IN I think it is better to leave some room for the alternator to also charge the 12v start battery and feeding the accessories.

Meanwhile i found this dc stepup (1800watt version)

https://a.aliexpress.com/_mMKz4UE

However i come see this setup is a little controversial. We don't know the mppt behavior v/s stepup. I will ask the seller if it's possible to wire these in parallel and how to isolate it to reduce the time constant effect on the capacitors.

 

[KlausST]

a 5A limitation on the SMPS OUT will draw 30A on SMPS IN

How do you know that it limits at 5A? A 5A rated one just says it can deliver it, but does say nothing about how it reacts in overcurrent.
Some will deliver more, some may have a fuse that blows, some may truely limit, but not exactly at 5A. Some may go into hickup mode... or, or, or...

Klaus

 

[Jake8]

How do you know that it limits at 5A? A 5A rated one just says it can deliver it, but does say nothing about how it reacts in overcurrent.
Some will deliver more, some may have a fuse that blows, some may truely limit, but not exactly at 5A. Some may go into hickup mode... or, or, or...

Klaus

I did try out its 1200watt little brother and that one had the same potmeters to adjust the va's. I measured 5a steady output at 65vcc and turned it down to 3,5 amps to limit the input amps even more. But somehow after a while it started to hickup and go on and off every 5 seconds. Then i measured 74voc at SMPS out and couldn't adjust the voltage anymore. Also i noticed a huge voltage drop when the device was going on and of becouse of some defect (not visual though, and the inverter was still generating +300watt in the few seconds it was on)

This made me think maybe it is better not to draw 30a on a 30a board, but get 2 even bigger smps in parallel. But again just for experimental reasons.

 

[Easy peasy]

there is no current limit on he Ali express converter - it is not controlled like a proper switcher

to work with MPPT, you need a soft rounded current limit.

 

[Jake8]

there is no current limit on he Ali express converter - it is not controlled like a proper switcher

to work with MPPT, you need a soft rounded current limit.

Sometimes the advertisements on ali show a perfect product but then in real life it can be a different experience.

Do you know where i can find a good current limiter?

 

[danadakk]

One way of telling how the limiter will function is look at pics of module, supply,
ascertain controller chip used, and look up that chips datasheet. Small modules
thats fairly good method. Usually low cost makers just use recommended data-
sheet application schematic. Larger supplies might be more difficult as limiting
may have more custom implementation, especially if supply capable of active
sharing.

Regards, Dana

 

[Jake8]

I see smps and current limiting is a time consuming option, also not very common and less easy to install than i thought. Also not very fool proof what makes selling the rv later on an issue becouse i don't want to electrocute the new buyer aswell as myself.

On my phone it is not very easy to draw but i think these are the options.
Offcourse the most safe and reliable is prefered.

Red= alternator>220vac inverter>growatt unit (chance of overload 12vdc to 220vac inverter?)
Blue= alternator>10amp lithium charger>parallel wired to lithium battery (chance of overcharge the battery is not a issue since the battery is with the bms over voltage/current/temperature protected
Green= smps+current limitation

Which option is preferable?

 

[BradtheRad]

I like to experiment with simulations like this quadruple interleaved boost converter. 14VDC stepped up to 75V 5A. It's not tested in hardware. It demonstrates levels of waveforms you can expect in such a system. It also tells what you're up against. Safeguards (such as current limiting) require further effort to install.

Four parallel SMPS joined into one. Duty cycles are staggered evenly. Just by chance each can run at 75 percent duty cycle. The analog switches make things simple.

 

[BradtheRad]

Another possibility is the Nakagome voltage multiplier. As load is removed or reduced, less current is automatically taken from the power supply.
On power-up the circuit draws large surge current for a few cycles until the capacitors are charged.

Capacitors charge to 13.4 volts each in parallel. They discharge in series (and add supply voltage in series).

My simulation has two interleaved multipliers, each multiplier is 4 stages (total 5x step up). Interleaving is a method to allow reasonably continual current to be drawn from the supply. Voltage never rises higher than the total of capacitors plus supply voltage.

I use analog switches to make things simple. Replace them with mosfets (properly chosen as N-devices or P-devices). The mosfets form H-bridges, several of them such that each capacitor connects between supply and ground during one half of the cycle, then to each other in a string during the other half of the cycle.

Assemble sufficient stages if you wish to obtain 75V 375W.

The link below runs this circuit in Falstad's simulator (animated & interactive):

https://tinyurl.com/26lbsqm8

Clicking it:

1) Opens website falstad.com/circuit,
2) Loads my schematic into the simulator,
3) Runs it on your computer.

Choose Toggle full screen (under File menu).