XW MPPT 60 questions

BobbyBobby Registered Users Posts: 8
I have done a lot of studying of your excellent web site and have learned a lot of good information. I have installed 4-210 watt evergreen panels, series into a XW MPPT 60-150 charge controller, charging 4 golf cart batteries at 12 volts nominal. My inverter is xantrax 1000 watt sign wave. I think the system is working well but I have a couple of questions about the XW Charge controller.

It seems the display on the XW reads about .3 volt low verified from two different other sources. (a Xantrax inverter in standby mode with no load and a Fluke 187 multimeter) With the XW in 12 volt default mode 14.8 Bukl and Absorb I have never seen it over 14.5 on the display. Also Float usually reads 13.2 or less.

I understand that I should charge these batteries at 14.8

With the XW in absorb mode reading 14.5 on the display I check at the battery buss and the voltage with the Fluke meter reads 14.1 I expect some loss threw the 10' cable from the XW but I really think the XW is just off by about at least 0.3 volt.

Is there any way to adjust the display voltage or charge voltage of the XW?

Or should I set the XW to Custom Battery and set the Bulk, Absorb, Float up three tenths of a volt?

The Batteries do read about 1265 on a EZRED Hydrometer. The battery bank is only about 2 months old. I use the power to run a small deep freeze, two condensate pumps and work shop lights. The XW does reach float mode every day so far.

What would you do, Complain to Xantrax (XW is less than a month old) or go to Custom Battery and change the settings or do nothing?

Your recommendations will be appreciated.


  • BB.BB. Super Moderators, Administrators Posts: 31,157 admin
    Re: XW MPPT 60 questions

    Some charge controllers display a temperature compensated battery charging voltage... So, if the battery (or charge controller) is at 77F, then the display should be the same as the measured voltage.

    Many times, charge controllers without the external (remote) battery temperature sensor tend to read "hot" which does reduce the true output voltage (hot batteries need lower charging voltage).

    Typical compensation is -5 mV/C (per cell, 25C/77F ref)... So, to be off by -0.3 volts, the controller would be:
    • -0.3 v / (-0.005 V/C per cell * 6 cells) = 10C (or ~18F high referenced to 77F)
    So, if you controller's ambient temperature while operating (controllers heat up with current flow), would be ~95F indicated.

    It is also possible that it is not dead accurate... A 2% error would be ~0.29 volts @ 14.5 volts.

    Many of the higher end units do allow you to tweak the calibration. Using an remote battery temperature sensor would help.

    And 10' cable run between controller/battery bank is a bit on the long side... What is the gauge and maximum current you usually see? It is easy to get a few 0.1's volts drop on such length of wiring under heavy current (my own two cents is that you should have a typical maximum of 0.05 volt wiring drop between controller/battery bank--perhaps 0.1 volt maximum).

    There are a few controllers that have remote battery voltage sense leads (some MorningStar and the new Rogue controllers)... It would be nice if more did. Accurate battery voltage measurements is pretty important.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • boBboB Solar Expert Posts: 980 ✭✭✭✭
    Re: XW MPPT 60 questions
    BB. wrote: »
    Accurate battery voltage measurements is pretty important.


    Yes, it sure is... Mainly when the system is in the Absorb cycle though. Voltage accuracy is definitely a good thing. If you have many Watts of loss in your battery cables, you really should have larger cables.

    Usually, in the Absorb constant voltage cycle, the current output is low enough that the voltage drop and accuracy is not a problem. In MPPT mode, the voltage is lower than the set point and doesn't matter unless the voltage reading is WAY far off. When charging is anywhere near Absorb voltage setpoint, the current has already started to drop. This assumes of course that the DC loads are not a significant part of the charging current.

  • Joe_BJoe_B Solar Expert Posts: 318 ✭✭✭✭✭✭
    Re: XW MPPT 60 questions

    My system uses two SCC's and I notice a .3 volt difference with one of them. The inverter and one SCC match pretty good but the other SCC is way off. I dont know if it makes a difference but I did disable cascading and set the odd ball SCC to .3 volts higher. Nothing bad happened but not much changed either.

    I think that if the system is networked, the first charger that changes modes, causes all the other charging sources to change to the same state. In bulk mode, it really does not matter what the voltage reading is because it is in current delivery mode but the absorb voltage is important. So techie at X once told me that if I wanted to "rent" a config tool for like $75, it is a tweakable parameter. I gave up on X making it right a long time ago.
  • BobbyBobby Registered Users Posts: 8
    Re: XW MPPT 60 questions

    I think the wire size from controller to batteries are #2 battery cable from tractor supply. I do have the battery temperature sensor it came with the controller.
    My maximum current is usually about 45 amps at 14.5 volts in the absorb stage. I do have some dc load during the time it is in absorb but usually not more than 15 amps. I assume that when the absorb current drifts down the rest of the output from the controller is available for dc load much like it is in the float mode.
  • BB.BB. Super Moderators, Administrators Posts: 31,157 admin
    Re: XW MPPT 60 questions

    Using a generic voltage drop calculator, 2 awg, 10' one way run, 45 amps:
    • 0.17 volt drop
    Fairly significant at high current levels... At least 3 awg larger, or one have the length to reduce the voltage drop by 1/2.
    • 2/0, 45 amps, 10' =>0.08 volt drop
    The problem with high current for 12 volt battery bank/systems... Need lots of copper to get the voltage drop down to "acceptable" levels for battery charging, running a large inverter, loads at a distance, etc.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • snuffysnuffy Solar Expert Posts: 72 ✭✭✭✭
    Re: XW MPPT 60 questions

    I think I'd make sure that the Fluke (assuming it's accurate) reads 14.8 at the batteries in absorb mode first. Adjusting the charger configs to make that happen. Then worry about what the CC meter reads after I got the correct voltage at the batteries. If you're reading 14.1 volts at the batteries in absorb now you're under charging the batteries.
  • silvertopsilvertop Solar Expert Posts: 155 ✭✭✭✭✭
    Re: XW MPPT 60 questions

    I also have two SCC's and there are slight variances in controllers on the led. I don't think this is a big deal; I slightly adjust the voltage in the custom settings to obtain what is correct on my Tri- Metric. That's where it's important, to keep those batteries happy!:D I slightly adjust the bulk, absorption, float and equalization settings to lock the voltage in exactly and haven't had any variance since.
  • BobbyBobby Registered Users Posts: 8
    Re: XW MPPT 60 questions

    Thanks guys, I am going to go with Custom Battery mode and ease the Bulk, Absorb and float voltages up untill I get the voltage at the battery to the correct reading.
    Thanks a lot. Common sense was telling me that that is what I needed to do. I will check on what I need to do to shorten my cables between charger and batterys.
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