Review: M4-ATX 6-30 volt Intelligent ATX Power Supply - The Third Time is the Charm!
Pros: Stable DC-DC power supply in small form-factor suits car PC's that need a little more power.
Cons: Single voltage output, buggy firmware, no software included to access the onboard USB port.
Overview
The M4-ATX DC-DC intelligent power supply unit (PSU) is the latest power supply from a company well-know in the car PC community, Mini-box. Following up the M1, M2, and M3 supplies, the M4 increases the power output to 250 watts, enough for more power-hungry in-car PCs. Able to briefly supply 300 watts peak during startups and able to operate from voltages as low as 6 volts or as high as 30 volts at the input, the M4 would be a great potential addition to the M-series power supplies and provides increased flexibility for unusual car pc installations (a lawn tractor pc, anyone?).
Issues
However, several issues keep me from giving the M4 an emphatic 'thumbs-up' including difficulty obtaining a working version to test due to buggy firmware and the lack of multiple voltage outputs as seen on other models such as the Carnetix 2140.
Mini-box advertises the M4 as 'intelligent,' meaning it has a USB header on the board that can be queried to change a wide variety of parameters such as the low voltage cutoff limit to prevent draining your car's battery, the ability to control the timing for when certain functions turn on, how long the power switch is held down for turn on and so forth. All this would be great, if Mini-box would mention it in the instructions. Alas, the only mention of the USB port is a diagram in the instruction booklet that shows the pinouts of the oddly shaped 10 pin header, which requires one to make their own cable from spare 5 pin connectors and a USB cables. Unfortunately, in early versions of the documentation the pin outs were improperly labelled, and the user guide never mentions the purpose of the USB connection or precisely what makes the M4 so intelligent, making the documentation effort feel hurried and last minute.
That's probably an apt description for my feeling about the M4. Disclaimer: As a mod on mp3car.com, I was shipped a free unit in exchange for a written evaluation to be posted on mp3car's review forum. Problems describing startup issues with early versions of the M4 began appearing in the forums on mp3car before I received mine for review. Intrepid users relayed their experiences with tech support and it surfaced that there was a bug in the firmware that prevented proper startup. Some users assisted Mini-box tech support by building their own serial cables to reflash the firmware and the problem was eventually pinpointed. It turns out my unit was one of these and a second M4 was shipped for the eval. Upon testing, it would signal my Intel D201GLY motherboard to start but seconds later the system would shut down. Again, another user reported the same problem. After much back and forth with tech support, another bug was found in the firmware that kept the M4 from releasing the power button after startup, causing a hard shutdown. Another unit was shipped and I am happy to report that the third time seems to be the charm as the M4 is now behaving as expected.
Still, Mini-box is a reputable and popular maker of car PC hardware and their M1/M2 supplies are widely used by hobbyists for DC installations. This is not their first attempt at an intelligent power supply -the M3 PicoPSU seems free of these afflictions and the result is that most of what is known about the M4 are the problems. The car PC community is clearly DIY, but frankly this cycle has felt rather more like a beta program. Even now, there are postings about the inaccuracy of the voltage monitoring in the latest version of the monitoring program for the M4 and problems with the anti-thump signal.
The voltage reporting for the M4 is inaccurate on some user's M4's
Note: Users on the mp3car forum have constructed a FAQ to help each other answer questions about the M4. The address is:
http://www.mp3car.com/vbulletin/powe...ur-m4-atx.html
That's too bad, because the M4 is a nice package. It's small enough to fit inside a regular ATX power supply case but powerful enough to run more than just the mini-itx form factors. In addition, the M4 includes a 4 wire cable for those motherboards that require one.
The M4 is small enough to fit inside some ATX cases.
Connecting the M4
Hooking the M4 to my car PC was straightforward, although it is helpful to have some knowledge of computer components. The evaluation unit that mp3car.com shipped me included the following:
1. M4-ATX mainboard
2. ATX power cable
3. Four wire jumper for main board
4. USB header to USB type A plug
5. Mini-box later shipped me an ATX enclosure to put the M4 in. Some users have indicated that it will fit inside a Dell Optiplex GX100 enclosure.
Input power
The input side of the M4 is simple. There is a terminal strip where you connect the ground to one side, the 12 volt always-on to the other and the ignition or accessory power to the center. The accessory power is also sometimes referred to as the 'switched' power in your car. When the key is inserted and turned, the power to this line is turned on. The M4 then signals the pc to start up.
Output power
I used an Intel Little Valley D201GLY mini-itx system to test the M4. The little valley is a low power consumption unit and was connected to a 3.5" 80 gig Maxtor hard drive.
Hooking it up was as simple as plugging in the ATX cable to the M4, then plugging it in to the motherboard. My motherboard also requires a separate 4 pin cable in addition to the ATX cable. Some motherboards such as the VIA M series boards that are popular with car pc'ers do not require this connection.
Presets
One thing Mini-box has done to help out the end user is to pre-program a set of presets into the M4 that you can change using a set of tiny 'dip' switches on the main board of the M4. These presets alter when the M4 cuts power to the 12 volt rails in the computer and also the 5 volt rails. The times for the 12 volt rails range from 5 seconds to 3 hours while the 5 volt rails ranges from 1 minute to never. This addresses the issue that even when in sleep mode, PC's supply 5 volts of power to the RAM to maintain settings and allow immediate resumption. The dip switches allow the user to choose from 8 different settings ranging from an 'always on' mode that simply makes the M4 function like a standard PSU to a 3 hour delayed off for 12 volt lines while never turning the 5 volt rail off.
The user simply sets the three dip switches to the proper on or off setting to activate the proper mode (Mini-box recommends mode 1, 5 seconds delay before cutting the 12 volt power and 1 minute before shutting off the 5 volt rail). Inexplicably, there are FOUR dip switches on the motherboard. Only the first three are used to activate the preset modes and apparently, switch number four is not used but the skimpy 5 page user guide makes no mention of this and never acknowledges a fourth switch, a very confusing situation, especially since the M4 needs to be disconnected from the power source for dip switch changes to register and I was confused at first that there was some secret fourth dip switch setting I was missing when trying to change the settings.
Users can use dip switches to choose preset functionality but the use of the fourth switch is never mentioned or explained.
The M4 seems aimed at competing with the venerable DSATX 220 watt intelligent power supply by providing more power for a lower price and the Carnetix 2140 185 watt power regulator, which trades for a slightly higher price but doesn't provide 'intelligent' features. However, while the M4 is advertised as intelligent, you cannot reflash the firmware via the USB port (unlike the 2140) and the only way to obtain a monitoring program for the M4 is to contact Mini-box's tech support. The M4 has perhaps two dozen parameters that can be changed, but since it uses a non-standard USB header and the program is not shipped with the M4, most users won't get the opportunity. In addition, the skimpy 5 page instruction manual doesn't mention or detail what the settings in the M4 are, so it is a guesswork situation.
In addition, the M4 does not provide dual voltage outputs like the more powerful (and more expensive) Opus 320. In order to provide stable, regulated output for a screen or XM box, one must tap into the 12 volt rail by hacking the cable. Perhaps this is the price of a lower cost intelligent power supply, but it does seem odd that Mini-box doesn't provide a Point of Load regulator like Carnetix does for its 2140 regulator for an additional charge. Although the 2140 is only a regulator, and not a full ATX power supply,it comes with two output voltages and the POL regulator adds a third.
Bottom line: Would I recommend the M4-ATX? Well, it certainly gives the most juice for the least buck, but it still has teething problems. Considering the fact that you can't really access the 'intelligent' part of the supply, the dismal and incorrect documentation, and the ongoing software and voltage inaccuracies, I'd have to advise to pass on the M4 until Mini-box gets it right and pay a little extra for the DSATX, or a lot more for the Opus 320. If you simply need a power regulator, take a look at the Carnetix 2140.
Love'in it
M4-ATX has been out for a while now, but...
Linear Mode
