14.8V charge on a Starting/Hybrid battery????

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Wanderman
Wanderman Solar Expert Posts: 180 ✭✭✭
in Off Grid Solar & Battery Systems #1
*** ARRRRGGGHHH..Title should be STARTING battery not STARING. Dumb...very dumb!***

OK..so I have been doing a lot of practical testing on my PV system in the RV. Everything works quite well. Even though it is flush mounted to the roof, I am seeing full charge (based upon usage) before 11AM on an average day. Peak has been about 370 Watts from the 48V nominal panels into the TS-45-MPPT Morningstar Controller. I am happy.

Now, since this is an RV, I have an additional battery used for starting the engine. I would like to have the ability to charge this to the same set points as the Trojan 27TMXs (2) that I have as house batteries. Does ANYONE make a hybrid or simple starting battery that will take charging up to 14.8V (like the Trojan Deep Cycles?)

My other choice is to wire a small 12V charger to the house system and charge the chassis/start battery with that. I do like the ability to tie them together, and when underway the house batteries charge from the alternator as well. (though only to 14.4V max...Solar gets them the "rest of the way" to 14.8)

Another question, what is the ACTUAL difference if the Trojans are charged to 14.7V instead of 14.8V? Just curious if it really makes any real world change.

Thanks,

Rich
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: 14.8V charge on a Starting/Hybrid battery????

    Thread title magically fixed! :D

    Normally a starting battery is charged to a lower Voltage than a deep cycle as you know. The specific Voltage depends on the particular vehicle, and it is usually temperature compensated. So in cold temps it might go to, say, 14.2 but I've never seen one hit 14.8 as Trojan recommends.

    So what happens if you don't bring the Trojans all the way up to 14.8? Not a lot. Shorter over-all battery life and a bit less capacity. A tenth of a Volt can be had in the tolerance of the meter reading it. What happens if you force the starting battery up to 14.8? Well it just might be too much for it; sealed battery pops its vent and gases. Not good.

    What is the solution? Don't do it, would be ideal. Use it for emergency charging only would be second. Third choice would be stick a big diode on the line so the solar can feed the starting battery but not vice-versa, and the diode will take about 0.6 Volts out of the equation bringing the charge Voltage down to something safer for the starting battery.

    I'm sure some of the other forum members will have additional suggestions.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #3
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    Re: 14.8V charge on a Starting/Hybrid battery????

    Why do you need to charge the starting battery from your solar panels? Doesn't the engine/alternator do it when you travel? Perhaps if you are parked for an extended period of time you just want a very small panel hooked up to the battery to keep it from self discharge. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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