"Smart" chargers

HorseflyHorsefly Registered Users Posts: 398 ✭✭✭✭
This isn't really a topic about renewable energy storage, but seems related. I figured people here were expert enough about charging lead-acid batteries that talking about car batteries would be OK.

For a while I've had a battery minder solar charger, with a small solar panel and the circuitry to manage the charge. It's only 270mA, and doesn't do much more than keep a battery topped off.  Silly me I wasn't using it, so during the stay home period my wife and I never had a reason to start either of our cars for maybe three weeks. Naturally when we do need to go someplace, both batteries were dead, or dead enough to not start.

I got by the immediate issue, and decided I needed another smart charger to keep the both batteries up. I decided to splurge, and got both a plug-in battery minder junior (750mA), and a Noco Genius10 (10A). The battery minder junior was about $25, and had no settings, and just a single LED that can be off, red, green, or flashing red or green. The Noco was $100 and had multiple LEDs as well as several different modes, including 6V or 12V flooded, 6V or 12V AGM, or 12V lithium.

I tried all three on our car batteries and monitored the voltages, and here's what I found.  Both of the battery tenders seem to behave as I might expect. They start out charging at about 14.5V, and after time go down to a float voltage of about 13.1V-13.5V. They will then hold that forever, or until they are not powered  (for the solar one, that's until the panel isn't exposed). The Noco does something completely different. It charges at about 14.5V until the battery is "fully charged" (their words) and then shuts off. It then monitors the battery voltage, and when the resting voltage gets to about 12.7V they start the charge again.  This cycle continues indefinitely, going from no charge to charge and back every 10 minutes or so. They never use float. I confirmed this with their tech support.

This makes me have a couple of questions:
  1. Is the Noco way of doing things - with no float stage - any worse than just keeping the battery at float?
  2. Would it be possible that Noco does this so that they can essentially use the same charging profile for both lead acid and Lithium, since Lithium batteries shouldn't have a float stage? Makes me wonder if under the hood this smart charger isn't so smart at all, and uses the same logic for flooded, AGM, and Li batteries.
I should say I like all three of these little chargers. My 30 year old dumb charger is on the brink of being thrown out, but does have jump-start 50A mode that I guess may be worth keeping.
Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 4 x Vmax XTR12-155 12V, 155AH batteries in a 2x2 24V 310AH bank.


  • jonrjonr Solar Expert Posts: 1,384 ✭✭✭✭
    Continuous float has a problem - there is no way to know the exact amount of voltage or current needed to maintain the battery - meaning it gets over or under charged.  IMO, adaptive maintenance charging algorithms are better.

    I am available for custom hardware/firmware development

  • mcgivormcgivor Solar Expert Posts: 3,712 ✭✭✭✭✭✭
    The no float algorithm is actually common in fire alarm systems, they use a timed higher voltage pulse to determine the state of charge, if the voltage cascades rapidly it confirms that there is no need to initiate a charging cycle. This will occur multiple times per day, kind of like a pseudo float without holding the voltage at above normal fully charged levels. For non cyclical loads such as standby or car battery maintenance charging, this method is ideal, unlike solar off grid where the battery gets depleted on a regular basis, which favors the float method.

    The use of solar as a maintenance charging method is something I've used on my tractor and escavator which often go unused for extended periods , a small 30W panel with a PWM controller seems to work fine because it turns itself off every night, a virtual 50% duty cycle in the tropics, when in daily use I don't bother using solar as the alternator is sufficient. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • HorseflyHorsefly Registered Users Posts: 398 ✭✭✭✭
    Thanks @jonr and @mcgivor.

    @jonr - I hadn't thought about the risk of under or over charging. I figured the charger would limit the current, but there isn't really any way for one of these little battery tenders to know how much current to allow. So it sounds like the Genius10 does the better thing. I just didn't expect it. At 4x the cost of the Battery Minder Junior, I guess it is worth it. Capable of a 10A charge, a repair mode, and (now I know) a better maintainer algorithm.

    @mcgivor - What you described for the fire alarm systems seems to be what the Noco Genius is doing. I've never seen the higher voltage pulse, but maybe it is happening. The answer I got from Noco was that when the battery drops below what the charger thinks is a 100% charge resting voltage it starts up. While it is charging the voltage is going back and forth between 14.9V and 13V, maybe a couple of times a second. 

    I bought the little Battery Minder Solar on Amazon a couple of years ago. We were vacationing overseas for about five weeks and came back to two dead batteries, so I went looking for a solution. It's cute: The panel is a little over 1 ft square, and the little charge control circuit is in a plastic box attached to the side of panel. I've recommended it to a couple of people for exactly what you described: Keeping a tractor or road grader while sittle idle for long periods.

    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 4 x Vmax XTR12-155 12V, 155AH batteries in a 2x2 24V 310AH bank.
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