testing the bulk charging MPPT for a 12 volt system

kevinhenrycalgary
kevinhenrycalgary Solar Expert Posts: 33 ✭
in Solar Beginners Corner #1
Hi guys,

I'm experiencing a bit of confusion. (not uncommon for me lately). Just testing a solar setup prior to shipping to a friend up North for installation in his cabin.

I ended up purchasing an EPSolar Tracer-4210RN MPPT controller (rated charge current of 40A,Discharge current of 20A, Max PV Input voltage of 100VDC. Max. PV Input power of 500W for a 12 volt system)to charge his 12 volt system with 24 volt panels. I will have two 230 watt panels in parallel but presently am just doing a demonstration video with one panel as he knows even less about Solar than me.

I am using an old 100 amp hour AGM battery that is sitting at about 10.7 volts. The battery doesn't hold a charge well but I was thinking it would be good for demonstration purposes as I wanted to demonstrate how many amps the single 230 watt panel could deliver to the battery in bulk MPPT mode. The battery and charge controller are at the same temperature 23C.

When I set the panel in full sun it seems to initially start bulk charging at upwards of 13 amps but then settles to a charge of 5.4 amps at 14.6 volts within a few minutes.

As I seem to recall that I was getting upwards of 11 amps from the 160 watt solar setup on my little trailer(in -20C weather, two 12 volt 80 Watt panels wired in series to charge a 220 amp hour 12 volt battery via a Morningstar MPPT controller) this value of 5.4 amps seems low to me.

Chances are I am misunderstanding something or is the fact that the battery is unreliable affecting my readings?

Should I install one of my good batteries after drawing it down to 50% or less in order to get higher bulk amperage readings.

Any pointers will be appreciated.

Thanks in advance.
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: testing the bulk charging MPPT for a 12 volt system

    What you're missing is that the charge is controlled by Voltage. By the time the controller 'sees' 14.6 Volts at the battery it will be cutting back on current because it's trying to maintain Absorb Voltage of 14.6. Nothing odd about that.

    The thing is the battery is clearly toast; it has no capacity so the Voltage rises quickly.

    If you want to load up the controller, put some DC load on the battery terminals to draw current even when Absorb set point is reached. One 230 Watt panel on a 12 Volt system through an MPPT controller ought to deliver 15 Amps or so. Without a "Watt equivalent" load on the output side you won't see that though.
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  • kevinhenrycalgary
    kevinhenrycalgary Solar Expert Posts: 33 ✭
    #3
    Re: testing the bulk charging MPPT for a 12 volt system

    Thanks for the quick reply. With my limited experience I was thinking that something was odd. I've got a couple of old AGM's that will be heading for recycling. I guess they weren't quite the good deal I thought they were! I am going to set the entire system up in the back yard today with both panels in parallel and two NEW 100 amp hour 12 volt AGMs in parallel.

    For the purposes of seeing the effects of the MPPT I will hook his panels up to the existing battery on my little trailer after I plug the vacuum into the inverter to put a load on and draw it down.

    Should I be inserting a single 15 amp fuse on the positive of each panel before it reaches the YMC4 connector or will a single 30-40 amp fuse be sufficient after the two positives are joined?

    Thanks again
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: testing the bulk charging MPPT for a 12 volt system

    Even with new batteries you will not necessary see maximum current: if they don't need it they don't get it. Once they are charged you would still need to supply a substantial load to realize the full current potential of the panels.

    With only two panels in parallel no circuit protection is required. They can not produce more than their Isc rating, which each is designed to handle anyway. Fusing the output of the charge controller is a good idea though.
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  • kevinhenrycalgary
    kevinhenrycalgary Solar Expert Posts: 33 ✭
    #5
    Re: testing the bulk charging MPPT for a 12 volt system

    Thanks again for the help. Everything is making sense. I don't deal with Solar every day so always have to refresh each time I tackle it. I'm just sizing and colour coding his wiring for him. I want to get everything together with proper wiring and fusing so he should have an easy install especially if I do a step by step video for him. Should be able to get it shipped to him as he's heading to his cabin the first week of June.
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  • robvizi
    robvizi Registered Users Posts: 3
    #6
    Re: testing the bulk charging MPPT for a 12 volt system

    Hi Kevin. Very interesting topic indeed. Thanks for your detail info, this is what im researching myself at the moment. If you dont get maximum current with a new battery it also can be the charge controller thing, this is what I dont like about these solar charge controllers that they dont work so efficiently as modern intelligent AC chargers do.
    " It takes what it needs" is not what a battery needs but what you get most efficiently out of it to save time and energy.

    An intelligent AC charger will charge the battery to 80% of charge at maximum available current and then slowly start to tapper off the current, however from what I see and hear that these solar controllers start to tapper off the current within the first hour of charge and dropping the current to ridiculous low, and this is not what a battery needs this just old inefficient way of charging that takes up 10+ times longer.

    If you could get a decent battery and update your charge info that would be really interesting. I have also found a charge controller by STECA which uses "Multistage charging technology" I hope this can provide more efficient charge rate than a regular one.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #7
    Re: testing the bulk charging MPPT for a 12 volt system
    robvizi wrote: »
    An intelligent AC charger will charge the battery to 80% of charge at maximum available current and then slowly start to tapper off the current, however from what I see and hear that these solar controllers start to tapper off the current within the first hour of charge and dropping the current to ridiculous low, and this is not what a battery needs this just old inefficient way of charging that takes up 10+ times longer.

    A typical AC or Solar Charge controller (good quality) will typically output maximum available current (with reasonable size battery) until the battery hits ~80-90% state of charge (bulk phase). At that point, the battery will hit the "absorb" voltage set point and then the charger should continue to hold the voltage for ~2-6 more hours then fall back to "float voltage".

    If you have a good battery bank, a charge controller should hold the rated output current (or a solar charge controller with full sun) until the battery voltage hits the absorb set point. If the charge controller starts to fold back current on its own after an hour of usage--Then the controller itself probably has some design issues.

    Trying to figure out what is happening gets more complex when you throw in solar charging... You have the state of charge of the battery bank (and level of sulfation), the charge controller (with temperature correction), and the amount of sunlight all playing against each other... It takes a bit of measuring/monitoring to figure out where the limitations are--And if everything is working correctly or if there is a problem.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #8
    Re: testing the bulk charging MPPT for a 12 volt system
    robvizi wrote: »
    If you could get a decent battery and update your charge info that would be really interesting. I have also found a charge controller by STECA which uses "Multistage charging technology" I hope this can provide more efficient charge rate than a regular one.

    It sounds like you've had bad experiences with budget/rubbish solar charge controllers. All of the controllers from the well known brands: Morningstar, outback, midnite, Xantrex (some), will do 4 stage charging (bulk, absorb, float, EQ) and will let you configure the voltage for each stage as well as the time spent in absorb.
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