specific gravity readings low. voltage ok

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TDIwestfalia
TDIwestfalia Registered Users Posts: 10 ✭
in General Solar Power Topics #1
I'm curious what you think of these readings for a 3 month old Trojan battery that is in my VW Westfalia. (SCS225 130 a/h) The battery holds 12.6-12.7 volts at rest after a charge and seems to work okay although it has not seen much use. After a week of sitting I have found the voltage at 12.5 with no loads on it. I was always told the specific gravity reading is the only good way to test a battery's charge regardless of what the voltage shows.

My hydrometer readings are low across the board (1.230 - 1.235 SG) while my voltmeter shows 12.7 (100%) This picture is 5 hours after a 10+ hr charge on an 8amp Battery Minder charger/ desulfator.

Trojan specs for a fully charged battery are 1.277 SG. Should I take this back or run it ?

I just took the battery to the local alternator shop that sells Trojans and he ran a 600 amp load on it for 15 seconds and it recovered. He says the battery is good and has no explanation for why the hydrometer readings are so low...Anyone ?

Thanks

20140629_171523.jpg
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: specific gravity readings low. voltage ok

    Welcome to the forum.

    That's not the best hydrometer design in my opinion. But better to trust the SG than battery Voltage. The reason is that a battery can go down in capacity while still displaying "correct" Voltage. It's the difference between an 'AAA' and a 'D': same Voltage, different capacity.

    You say you charged it for 10 hours at 8 Amps. What with? How high did the Voltage go? Trojan specs 14.8 for Absorb Voltage, and if the Voltage was not high enough it will not be charged properly no matter how long you charge it for.
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  • TDIwestfalia
    TDIwestfalia Registered Users Posts: 10 ✭
    #3
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    Re: specific gravity readings low. voltage ok

    Thanks for the welcome. I have a feeling I will be here a lot. I'm wiring in a xantrex and solar this week.

    I charged it with a battery minder 12248. I believe it only charges at 13.8 volts max. When I went out this morning it was in float mode at 13.0 volts. I have read about the Trojans needing to be charged at 14.8. My new solar controller is adjustable and I will set it at 14.8 Do you have any suggestions for a regular charger that can do 14.8 ? I always thought if you charged long enough the battery would get to full capacity regardless... I guess I have been wrong.

    I was going to buy the IOTA 45amp DLS w/ IQ from this site but I can't get a solid answer on whether it does 14.8 or not. Some people say it do. Others say 14.6
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
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    Re: specific gravity readings low. voltage ok

    Chargers tend to be Voltage controlled: once they reach 'X' Volts the current drops off and that Voltage is maintained. If it's too low a Voltage the battery is never brought up full.

    Stand-alone battery chargers that can do a proper job on deep cycles (especially ones requiring higher Voltages like Trojan) are few. You can crank up an Iota http://www.solar-electric.com/bach1.html if you open it up (skip the IQ4 option).

    PNJunction likes his new Samlex charger http://forum.solar-electric.com/showthread.php?23890-Samlex-SEC-1215UL-charger but it using at at lower Voltages.

    There is always the nasty manual charging option of gutting a cheap automotive charger and just using its transformer and rectifiers, but you must watch the Voltage and regulate it manually. This means turning on and off as needed. It will do in a pinch but it's not the safest thing in the world.

    Or you could use it in conjunction with a PWM charge controller to regulate the output. Just be sure the controller can handle the current (provide over-current protection in and out of the controller) and that it will allow you to set the Voltage level you want.
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  • TDIwestfalia
    TDIwestfalia Registered Users Posts: 10 ✭
    #5
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    Re: specific gravity readings low. voltage ok

    Thanks. I have just one battery right now but will be adding another SCS225 when I add a truckfridge down the road. Is the 30amp IOTA sufficient for this ? Are there instructions online for adjusting an IOTA or do you have to call them ? I havent found anything online yet. I will be making an order later this week. Thanks !
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
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    Re: specific gravity readings low. voltage ok

    Two of those batteries in parallel would be 260 Amp hours so yes a 30 Amp charger should be sufficient. There's information somewhere on this forum about adjusting the Iota's output Voltage. It involves opening the case and turning a small potentiometer inside while measuring the output. I believe Blackcherry04 can tell you exactly how to do this.

    Now here's the problem: paralleling batteries isn't the best idea in the world and needs to be done carefully to keep current sharing even. With two batteries in parallel this is fairly easy: you connect them together and then make all positive connections to one and all negative connections to the other.

    Now here's another problem: you've already used these batteries and they have not been recharged in the best manner. That means and 'identical' new battery will not actually be identical to the 'aged' battery. How much different they are is anybody's guess, but it ultimately will shorten the life of the new one by some amount even if nothing else goes wrong.

    Neither of these problems is an immediate catastrophe; it just means things won't be as good as possible and may get worse.
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  • TDIwestfalia
    TDIwestfalia Registered Users Posts: 10 ✭
    #7
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    Re: specific gravity readings low. voltage ok

    I just ordered the IOTA 45 amp with the separate plug in IQ4 from this site. I have been researching the voltage adjustment on the IOTA . I think I got it.
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  • TDIwestfalia
    TDIwestfalia Registered Users Posts: 10 ✭
    #8
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    Re: specific gravity readings low. voltage ok

    My wrenching friend said I messed up by getting the 45amp version as it will shorten the life of my one battery greatly(130 a/h). That's not right is it? If its not charging above the needed voltage I figured it doesn't matter. I thought it would charge up to 45amps if it was completely dead....while charging it back from a 50% discharge it would never get near 45amps. I just starting to read the book managing 12 volts right now and there isn't much on selecting a charger. I am quickly finding out 130 a/h is plenty for my westfalia/ mods so I may not add more juice down the road. would you exchange for a 15 or 30amp model or did I just pay a few dollars more for no reason ? The price difference between the 15a-45a models isn't much so I went big just in case I added more later. Thanks
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
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    Re: specific gravity readings low. voltage ok

    Possibly a problem.

    A battery only takes as much current as it will, regardless of the charger's capacity. Unfortunately batteries aren't smart and can be depleted to where they will draw more than they should. So yes, in theory but hopefully not in practice you could be putting 45 Amps to a 130 Amp hour battery: a 34% rate. That the battery will not like; it can heat up too much, boil off electrolyte, warp plates.

    On the other hand I just charged my tiny mower battery with a 30 Amp manual charger and it didn't burst into flames. The trick is to not let them get so low in SOC (and thus resistance) that they draw huge amounts of current that isn't good for them.

    If you're sticking with the one 130 Amp hour battery I would go with the 15 Amp charger though. That would be plenty.
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  • TDIwestfalia
    TDIwestfalia Registered Users Posts: 10 ✭
    #10
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    Re: specific gravity readings low. voltage ok

    Oops. I will get this exchanged. Thanks for the help.
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