1990 Westfalia - 2 Batteries, 3 charging sources (Alternator, Solar PV & Bat Tender)

infliction1infliction1 Registered Users Posts: 3
I have a 1990 VW Westfalia Camper with an Aux battery (AGM) bank and a starting battery.
With the Go Westy Isolater set-up the Alternator will charge both batteries when running and isolate the two batteries when engine is off.

I recently installed a 100W Renogy solar panel with their 30W MPPT charge controller (currently connected only to the Aux Battery).
I also have installed a small battery tender connected to the shore power lines in the bus to charge the starting battery during winter storage.

My starter battery has a parasitic draw that runs the battery down when sitting for about 1 week. (problem)
I have no issues with the aux batteries running all the electronics when bus is parked and/or camping.

My questions are as follows:

A) Can I connect a manual switch (1, 2, Both or Off) to connect both batteries for charging by solar when parked or camping? (Solar can be tuned off via 20A Circuit Breaker before starting the bus and the manual switch would be set to off before starting the bus to allow the isolater to work as designed when driving.

B) Would there be problems if I connected my battery tender to the same manual switch? Knowing that the battery tender would only be used when parked (engine off) and connected to shore power.

C) What are the concerns with running the solar system and battery tender charging systems at the same time?

D) What am I missing? Are there snakes in the grass with these three systems potentially running at the same time (only by user error)?

Thanks, I am new to this forum, solar power and DC electric systems in general. (i.e. A omplete Newb)



  • EstragonEstragon Registered Users Posts: 3,118 ✭✭✭✭✭
    As a general proposition, there is no problem having multiple charging sources connected to a battery (or bank). The charging sources aren't sync'd though, so (eg) the pv charge controller may "wonder" why voltage from another source is keeping battery voltage high when the controller thinks it should be floating. As a rule, this doesn't hurt anything though.

    There can be an issue with multiple banks though if the batteries have different charging needs (eg Gel or AGM starting battery needing lower voltage charging than a flooded house bank, or batteries at much different temperatures - the hot AGM in an engine compartment could get cooked with voltage regulated by a charge controller for cool/cold flooded batteries in a house bay).
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mcgivormcgivor Solar Expert Posts: 2,484 ✭✭✭✭✭
    A potential snake in the grass is a starting battery is not well suited to deep discharge, if drawn down by house loads the ability to start may become an issue, should the switch be left on both. Resolving the parasitic load issue on the start battery would be my priority, have you actually confirmed this, or is it perhaps a weak battery that can't hold a charge? As mentioned different battery designs flooded /AGM require different charge voltages, the alternator is regulated for the flooded start battery, this may subject the AGM house battery, which requires a lower voltage, to vent gas, which is not a good thing, unlike a flooded battery which can accept abuse, within reason of course.

    A marriage between incompatible individuals often ends in heartbreak, for this reason my thoughts are to keep the two battery systems apart by having seperate charging systems for each, just my opinion others may differ.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system. 
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
  • mike95490mike95490 Solar Expert Posts: 8,063 ✭✭✭✭✭
    How smart is the battery tender ?  real smart ones could be fooled into shutting down from rising voltage from the PV panels, but nothing bad should happen to the batteries - As long as all charging sources are optimized for the battery they are charging.
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • infliction1infliction1 Registered Users Posts: 3
    Thank you all.

    I suppose one idea would be to put a small charge controller between the Go Westy isolater and the house battery to control the alternator charge voltage and prevent over-cooking of House battery.

    I will definitely resolve the parasitic draw issue as well. The starting battery tested okay last year, but will test again.

    I’m thinking that the battery tender is smart enough to prevent self injury if by chance accidentally paralleled with the solar charging system.

    The manual over-ride switch will only be employed for a) winter storage via BT b) Solar charging of both banks or c) if by chance the starting battery falters.

    Thanks again guys!
  • fratermusfratermus Registered Users Posts: 22 ✭✭
    mike95490 said:
    How smart is the battery tender ?  real smart ones could be fooled into shutting down from rising voltage from the PV panels, but nothing bad should happen to the batteries
    I have heard my Battery Doctor (VSR) disconnect when solar took the house battery into the mid-14v range.  It's not a published feature but it has happened often enough I think it's built that way.

    Here is the scenario as I observe/understand it:
    1. engine off, VSR disconnected.  Solar is charging house bank.  House bank may be >=13.4v but VSR can't tell because it reads voltage on chassis battery side and hasn't connected the two banks.
    2. engine on, starter battery up to 13.4v, VSR connects (click!)
    3. engine off, VSR stays connected because it reads >=13.4v on the starter battery side because solar keeps house battery >=13.4v
    4. Bulk charging progresses toward Vabs;  VSR disconnects at ~14.5.

    2017 Promaster 159" DIY camper
    570W mono / 220AH GC
  • infliction1infliction1 Registered Users Posts: 3
    Thanks Fratermus
    One more question (Sorry)...

    I see dual sensing VSR (Voltage Sensitive Relays) on the market [still learning these acronyms].

    Does the dual sensing mean that if the solar system charges the aux battery above a certain voltage that it also starts charging the start battery?

    Seems like a great solution for most RV solar set-ups, but I don't want to get in over my head and start cooking things the wrong way.

    Perhaps I'm confused...

    Best, SRJ
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