Using 36 Volt generator/alternator to charge house betteries?

Hello Everyone,

I am installing solar and upgraded house batteries in my RV. I will have a 24v - 370A/H battery bank and need backup charging for times when solar production is not adequate.

I have come across a diesel 36v generator. Basically a small diesel motor with a 36 volt alternator.

What I am considering is using the 36 VDC generator to feed a 40A MPPT charge controller to charge my 24v battery bank.

My RV is diesel and I don't want to have to carry gasoline. Otherwise I would buy a little Honda inverter generator.

What do you all think of this plan? Suggestions?




  • mike95490mike95490 Posts: 7,613Solar Expert ✭✭✭✭
    you might  a 24V truck Voltage regulator to fit onto it.  Otherwise you are looking at some real kludges to "maybe" get it to work with a MPPT controller.  2.2wh / 36V = 60A alternator, and still 60A (because that's all the internal wires can handle) downgraded to 24V.

    A high end MPPT controller could down-convert it to as much as 90A

    But slapping a $30, 24V truck voltage regulator would be easiest.  Adding a 12V zener to the voltage reference line of the existing regulator could work also ($5 zener, $60 for an engineer to design it)
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • BB.BB. Posts: 27,354Super Moderators admin
    Many vehicle alternators have a voltage regulator that is not capable of generating a stable DC voltage. For example car alternator systems can generate 100 VDC or more if the car is still doing and then the battery is disconnected (and wipe out the lights and electronics on the DC battery but).

    Although, there are DC generator sets that are perfectly capable of generating a stable DC output voltage (running DC equipment directly without batteries).

    See if you can find documentation on this unit and see if it gives stable 36 VDC. And / or start it up and measure the output voltage (use 3x 12 volt filament bulbs in series for a cheap 36 volt load).

    If stable then connecting a good mppt charge controller should be fine.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PNW_StevePNW_Steve Posts: 37Registered Users ✭✭
    I am waiting on documentation from the manufacturer.

    I am hoping that I may be able to use one of the Balmar multistage regulators with this alternator.

    But I am pretty much on hold until I get docs from the manufacturer.
  • PNW_StevePNW_Steve Posts: 37Registered Users ✭✭
    I have been waiting patiently for documentation.

    The gent that I spoke with at Mechron seemed very agreeable to sending it. Now he has gone silent.

    Anyone here recognize the alternator on this unit?

    Maybe I can find docs on the alternator from the OEM?
  • BB.BB. Posts: 27,354Super Moderators admin
    Fire it up with some lights or electric heater as loads (don't care loads that could, in theory, get called). Put a meter on the DC bus and see if there voltage is stable with resistive load, and with no loads.

    I am guessing that its output voltage will be stable (i.e., a good DC supply without batteries as buffer).

    Running without loads should not cause any damage to the alternator (don't rev the engine. That could raise DC voltage and damage rectifiers or regulators if was designed for battery charging only).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonrjonr Posts: 949Solar Expert ✭✭✭✭
    It's probably 28V nominal with the exact voltage being rpm dependent.   Maybe here for manuals:

  • PNW_StevePNW_Steve Posts: 37Registered Users ✭✭
    I want to confirm whether it is 24 or 36 volt before I put power to the starter.

    The gent that I bought it from told me that it was 36v. I am beginning to suspect that he was mistaken and it really is 24v.
  • BB.BB. Posts: 27,354Super Moderators admin
    edited May 13 #9
    There is a small chance that this is a 120 VAC 60 Hz alternator too... Did a search on "mechron 27B" and came up with a couple of auction listings: (don't know if link output is "stable" over time or not)



    Mechron Power Systems Inc mdlASB 2D/DND7 2kw diesel generator, ser# 27B7809V, hours 0016.7, year unknown, volts 120vac 2 wire + ground. Motor turns when pulling cord mechanism. Note: injector is loose in unit. Please click on the PREVIEW AND LOADOUT tab above to see information on new base access procedure effective April, 1st 2016. GL will provide tail gate loading.

    Mechron Power Systems Mdl ASB 2D/DND7 2 KW 60 Hz diesel engine generator set Sn 27B7369V2, meter indicates 46 hours, 120 VAC, 18.3 Amp, includes Yanmar engine, dimensions 30 X 16 X 22, GL will Provide Tail Gate Loading

    Looking up the "alternate" Mechron part number(s) from above, got a link for:

    The open frame configuration is available as follows:

    Power Output Dewey Model PM-MEP Model NSN P/N
    28V DC -501A MEP95-501A 6115-01-435-1567 95-501
    120V 60Hz -531A MEP95-531A 6115-01-435-1565 95-531

    On that same page, some model links:

    Download Data Sheets

    The photos I could find show a switch gear box on the back of the genset--With, I pressume, Voltage/Amperage/Frequency (if AC) meters.

    Search for "Mechron Power Systems Mdl ASB 2D/DND7" on DuckDuckGo or Google and see if you can find anymore supporting documentation (I got "here" by searching for "Mechron 27B diesel generator" guessing that "27B" was some sort of model number).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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