Is it necessary to replace the SMD fuses in RAMPS 1.5 or greater, for use with 24 volts?

Question

One of the main hacks for converting RAMPS 1.4 boards to use with 24 V, as stated in RAMPS 24V, is replacing the polyfuses, principally F2 (MF-R1100), with wire and using an inline (car blade or wire) fuse on the heatbed wire (or between PSU and RAMPS) instead¹. However, that is for the RAMPS 1.4 boards.

As RAMPS 1.5 notes (as well as 0scar's answer to RAMPS 1.4, 1.5 or 1.6?):

The RAMPS 1.5 uses small surface-mounted fuses rather than the large yellow fuses prone to breakage on the RAMPS 1.4. The downside is that replacing the fuses becomes much more difficult.

Are these SMD fuses rated the same voltages, or greater? Yes, this could be a bit like asking "How long is a piece of string" as it depends upon the manufacturer, but does anyone know what voltage should they be rated for?

Ultimately, if they are both rated at greater than 24 V, then there should be no need to replace them.

The answer on this thread, Re: Ramps1.4 or Ramps1.5 or ramps 1.6??? states:

OK the ramps 1.6 can only handle 12v OR 24V

so, that would imply that the intention for 24 V support was there, although, unfortunately, the poster does not post their reference.

However, the PDF of the RAMPS 1.6 schematic shows the same rated fuses as the RAMPS 1.4

Nevertheless, that seems like a straight forward copy and paste from the RAMPS 1.4 schematic as it clearly references the MF-R500 PTC, and obviously SMD fuses have been used instead - or are the part numbers the same for the SMD fuses..? I had a google but couldn't see MF-R500 SMD fuses (maybe I didn't look hard enough?).

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Footnote

¹ This is because the 11 A fuse is only rated to 16 V. Note that F1 (MF-R500) is rated for 5 A at 30 V, and as such is sufficient for 24 V operation.

Answer 1

Without knowing the exact part numbers used for F1 and F2 it is impossible to say whether the fuses need to be replaced or not. However, based on the manufacturer provided schematic and BOM we can make a pretty good guess.

Looking at the PDF you linked, it states that F1 is rated for 16V. Looking at the BOM spreadsheet it also says F1 is 16V and 30A.

Based on the fact that the only two reference documents available say 16V, I would strongly recommend replacing this component for 24V operation.

Answer 2

I found that at least the following two RAMPS 1.6 derived boards are 24 V capable without modifications:

• Bigtreetech RAMPS 1.6 Plus (see the PCB layout picture in this offer)
• King Print RAMPS 1.6 Plus

This information is so far only from webshop offers, so might not be the most reliable (and I did not test it myself yet). If somebody can find a confirmation from the manufacturer's spec documents, please let me know.