Why use 19v for RAMBo?

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javafuel
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Why use 19v for RAMBo?

Post by javafuel » Tue Jun 09, 2020 4:51 pm

My 8 years old M2 came with two bricks PSU, a Dell 12v 18a for heatbed and a 19v 6a for everything else even though all the fans are rated 12v. I'm curious as why did Makergear use 19v? I'm in the process of adding E3D Titan and V6 hotend to the M2. I'll be replacing 19v brick with a Meanwell 12v 12.5a PSU from drone charger.

airscapes
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Re: Why use 19v for RAMBo?

Post by airscapes » Wed Jun 10, 2020 1:24 pm

I am going to guess here.. Over sized to prevent it from running at max output all the time. Better to have more power and step it down than not enough. Has a power supply ramps up and heat goes up output goes up, voltage can drop.. Did a quick google on the subject..
https://www.google.com/search?q=voltage ... e&ie=UTF-8

javafuel
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Re: Why use 19v for RAMBo?

Post by javafuel » Wed Jun 10, 2020 7:07 pm

Makergear says v19 is mainly for the hotend.

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ednisley
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Re: Why use 19v for RAMBo?

Post by ednisley » Thu Jun 11, 2020 2:34 pm

javafuel wrote:
Tue Jun 09, 2020 4:51 pm
a Dell 12v 18a for heatbed and a 19v 6a for everything else
The 12 V platform heater was a catastrophically bad mistake, because the heater draws far more current than the wires & connectors can handle:

https://softsolder.com/2019/03/12/maker ... g-failure/

If the connectors at the RAMBo haven't already charred, consider yourself inordinately lucky.
replacing 19v brick with a Meanwell 12v 12.5a PSU
That will pretty much wreck the printer's performance, because the stepper motor winding current's rate-of-change depends on the supply voltage, with 19 V being marginal.

I've looked into this problem several times:

https://softsolder.com/2017/11/29/mpcnc ... xis-speed/
https://softsolder.com/2018/01/26/mpcnc ... -back-emf/
https://softsolder.com/2018/02/02/mpcnc ... f-madness/

The absolute best thing you can do with that relic is upgrade it to 24 V with a V4 hot end and platform heater, plus replace the Z-axis motor. It's expensive, but it'll avert an unending series of "Why did this just happen?" problems.

The M2's mechanics remain solid, but the electrical & electronic parts have seen considerable improvement over the years …

javafuel
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Re: Why use 19v for RAMBo?

Post by javafuel » Thu Jun 11, 2020 5:42 pm

If the connectors at the RAMBo haven't already charred, consider yourself inordinately lucky.
Yes, mine has charred twice. I now have a big MOFSET for the headbed power, it seems to be OK now.


That will pretty much wreck the printer's performance, because the stepper motor winding current's rate-of-change depends on the supply voltage, with 19 V being marginal.
Slow performance is not ideal, but I'm ok with it as long as the print quality doesn't suffer.

The absolute best thing you can do with that relic is upgrade it to 24 V with a V4 hot end and platform heater, plus replace the Z-axis motor. It's expensive, but it'll avert an unending series of "Why did this just happen?" problems.

The M2's mechanics remain solid, but the electrical & electronic parts have seen considerable improvement over the years …
Upgrading it to 24v is definitely the way to go, but it's expansive and time consuming process. I've put a lot of money in it over the years. It's almost better to get a $350 direct drive printer from Amazon that is 90% assembled.

Thanks Ed for the great insights

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ednisley
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Re: Why use 19v for RAMBo?

Post by ednisley » Thu Jun 11, 2020 6:44 pm

javafuel wrote:
Thu Jun 11, 2020 5:42 pm
get a $350 direct drive printer from Amazon
A friend did that and had a good out-of-box experience, then added a few hundred bucks of this-n-that to bring it up to solid usability. You've already got much much better hardware, apart from the (probably) crap Z-axis motor [1], so it's better to drop the money on upgrading the hot end (which you were going to do already) and the platform heater (which you should do). The money will be a wash and you'll have a better printer when you're done.
as long as the print quality doesn't suffer
When you start wondering why the steppers sometimes miss steps, you'll know the reason.

Note that the E3D comes in 12 V and 24 V versions, so you'll be stuck with a high-performance 12 V hot end on a low performance 12 V printer.

Don't buy yourself into a dead end …

[1] To check the Z-axis motor, measure the winding resistance:

https://softsolder.com/2013/04/10/maker ... per-motor/

tl;dr: if the windings measure more than a few ohms, replace the motor:

https://softsolder.com/2013/06/28/maker ... ransplant/

MG now has a drop-in replacement, so do that, even if it's a bit more spendy.

javafuel
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Re: Why use 19v for RAMBo?

Post by javafuel » Thu Jun 11, 2020 7:57 pm

When you start wondering why the steppers sometimes miss steps, you'll know the reason.

Note that the E3D comes in 12 V and 24 V versions, so you'll be stuck with a high-performance 12 V hot end on a low performance 12 V printer.

Don't buy yourself into a dead end …
I've already bought 12v V6 in 2018, after the v3b hotend you gave me started leaking (it was my fault, but I did got many good prints out of it). Then life happened, never gotten the chance to install it. My M2 has been sitting in the enclosure for over two years. That tells you how much printing I do haha.

Eventually I'll upgrade M2 to 24v, now I just don't have to time and want to spend as little as possible to get it going again.

In order to use 12v V6 hotend that I already bought while keeping steppers performance. I can power RAMBo like this, right?

Snipaste_2020-06-11_11-50-20.png

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ednisley
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Re: Why use 19v for RAMBo?

Post by ednisley » Fri Jun 12, 2020 2:03 pm

javafuel wrote:
Thu Jun 11, 2020 7:57 pm
power RAMBo like this, right?
Seems reasonable. Having two separate 12 V supplies may seem excessive, but isolating the logic from the platform heater's killer current is a Good Idea™.

Not running that current through the RAMBo is even better, which is what you're accomplishing with the external MOSFET switch. Good work!

When the time for an overhaul arrives, replace the hot end's 12 V cartridge heater with a 24 V version and be done with it.

javafuel
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Re: Why use 19v for RAMBo?

Post by javafuel » Fri Jun 12, 2020 4:49 pm

Thanks for all the advice, Ed. I really appreciate it.

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