I'm wondering what's up with yhour MX60.  You didn't post your input/output voltages
and currents (real currents), which is very important.  Is it that the OUTPUT Ammeter of this particular MX60 is wrong, and are you using some external monitoring ?

The MX60 will have a lower efficiency at low output power/voltage/current.
83% is very low for medium to high power outputs, even 12V systems.

Outback has a user forum on their website with some pretty experienced installers and users. I've been browsing it for some time and have never heard of your complaint before. Maybe post a message over there and see what those folks say.

Street price on an MX60 is as low as $460 now. Don't pay list, you can get them much cheaper.

Volvo Farmer

but here they are

input voltage       mx60 indicated     meter one       meter two
.                          60.0               60.0            60.0

input current            3.9                 3.9             3.9

output voltage        13.2                13.2           13.2

output amperage     * 6.9 *                 5.7            5.7

as you can see the two external test meters agree with outbacks screen on input and output voltage and input current,, but disagree significantly on output current.

when we called outback we were told they compute the output current and do not actually measure it!  so... how do you get accurate efficiency computations if you compute one of the variables and it is so far off of reality?

this is why i would like to see someone else check their output current externally and compare it with the screen indicated current.

volvo farmer:

yes i am aware that they can be had for about 450, but even at that level
i want to see better efficiencies (actual) not calculated based on some fuzzy math.

yes these are being tested on a solar array, we tested them with various panels of various wattage input and from 30 volts input to 80 volts input,, and got very near the same results in efficiency with actual readings. and coincidentally the screen still computed mid to high 90 efficiency, which is apparently a flawed result.

thank you both

anyone got one they can test the output on?

I have been working a lot with the designing of switched DC/DC converters.
and the result you are describing is a Waste.
To be honest I have newer seen any switching application that gives as high real world efficiency as
stated 98% by the MX60, but then again the MX60 is probably not switching then.

Reading the "MX60_a.pdf" it tells that the
Power Conversion Efficiency Typical
98% at 60amps with a 48V battery and a nominal 48V Solar array.
(Probably working linear at the time displaying the internal loss in RDSon.)
This really tells U nothing of the product.
A coversion table would be nice though.

however the info about the output amps being calculated and the input amps being actually measured was from outbacks technical support.

they told us the unit measures input voltage and amperage
and also the output voltage
but the output amperage is calculated and not actually measured.

My MX60 is still working (the replacement one) ....
its been a couple years now...

The MX60 and all converters have high efficiency when the input voltage is close to the output voltage.

98 % efficiency means that the converter is having a high duty cycle, like 96 + % which allows the power MosFets to be most of the time ON, looking , ALMOST, like a charger controller like the C60, which is a DC switch with a very low ( around 200 Hz) modulation frequency that starts to switch when the battery voltage is reaching the controller limits.

The use of a converter with high input voltage to bring down to low voltage, is an erroneous decision.

One should and ought to do a design consideration of the conversion to attain high conversion efficiencies and these efficiencies will run around 83 to 92 %.

To attain high efficiencies when converting from a high voltage to a low voltage, like in this case, the converter should have a transformer conversion to increase the efficiency.

Since you need a high current( 240 amps) then what I suggest is a full bridge feeding a synchronous dual current rectifier.

Go to www.ti.com and down load the UCC3895 device and the : slua107.pdf; slua121.pdf; slua275.pdf; slua287.pdf; slua323.pdf; slua189.pdf -- that may teach you what the best procedure to follow for this project.

You are looking for a charger system that is around 3.5 KW, a major project, INDEED,that unless you are quite familiar with high power design procedures, my suggestion is to look for other alternative solutions, like several in parallel with sequential ON-OFF sections for higher efficiencies ( a multi phase system with ON-OFF capabilities ) and with MPPT control to maximize the charging efficiency.

Do not trust the currrent display of these converter, they are relative and many times not very accurate since the do not need accurate calibration for external display, but relative current levels for internal limiting conditions.

If tests aree neded, then proper current meters are needed, for accurate determination of the needed parameters.

In this case the design should have a push-pull or a full bridge feeding a transformer with efficient rectifiers this way one may obtain around 89 to 94 % conversion efficiency.

LASTLY: since you have such high KW conversion to a low voltage, one should examine the system and see how to improve it overall, for one, a much higher BATTERY voltage is suggested being 48 volts which that may give you and additional 5 to 8 % higher efficiency overall in usage up DC/AC conversion.

Then a more reasonable charge controller can be used which in this case a single MX60 may do the job -- or one a bit bigger like what Midnite Solar may be putting in to the market soon.