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Variable dc power supply 0-3 amp 0-150Vdc

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  • 21-07-2014 1:15pm
    #1
    pedronomix
    Closed Accounts Posts: 997 ✭✭✭


    I have some NiMh cells that I need to charge to 135 vdc or at least above 100vdc at low power <1.0 amp. Any ideas where I could borrow/rent/buy a cheap charger.

    Thanks

    Peter


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    #2
    spideog7
    Registered Users Posts: 1,230 ✭✭✭spideog7


    pedronomix wrote: »
    I have some NiMh cells that I need to charge to 135 vdc or at least above 100vdc

    I assume you mean a NiMh battery? NiMh Cells are typically 1.2V and they should be charged at about 1.4V, so I think your range (100V to 135V) is a bit large.

    Do you want to charge to 135V or do you want a charge voltage of 135V? A charge voltage of 135V might be appropriate for a 100V nominal. How many cells do you have (around 85?)?


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    #3
    pedronomix
    Closed Accounts Posts: 997 ✭✭✭pedronomix


    Should have included the word array or some such term , sorry, my fault. Yip, they are in an electric vehicle and I need to get them above 100v for the built-in charger to kick in. Currently ( pun intended) only 42v on tap!! As I understand it, they stabilise at 135v when full charged. 102 cells series linked. I am a complete novice so plain speak really appreciated.

    Thanks

    Pedro


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    #4
    spideog7
    Registered Users Posts: 1,230 ✭✭✭spideog7


    Right so you want to charge them with a constant current not a constant voltage. Which means unlike a resistive load (say a light bulb) where you put a constant voltage across it and it pulls as much current as it needs, you'll be pushing a current through it and the voltage will adjust to ensure that current can flow (basically the voltage will ramp up to match the battery voltage).

    You want a really low charge current, what is the rating of your pack? You want to be in the region of 1/100 or a 1/50 of the rated current. You have 102 series cells but you also likely have some number of parallel cells to provide a high current rating. Individual cells are unlikely to be rated higher than 2200mAh at a guess which is unlikely to be sufficient for an electric vehicle and 1A would be too high to charge that at.

    More details of how you ended up in this situation and what the full specs for that battery are would be helpful to ensure you don't produce smoke. To supply that kind of voltage and current nine standard 12V car batteries would do it, but remember you need constant current not constant voltage, so don't just connect them up.

    Also be aware that your cell voltage is currently less than 1V so they're dangerously discharged and you could have some damaged cells (depends on the circumstances of how they got that low I guess). Anyway assuming the internal charger has cell balancing and all the other fun stuff required to ensure the pack gets an optimal charge you just need to get that pack high enough for the internal charger to kick in.


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    #5
    pedronomix
    Closed Accounts Posts: 997 ✭✭✭pedronomix


    Thanks spideog7, even I understand your post!

    It is a Vectrix V1 3.7 KwH large maxi scooter, not a car. I have a set of Nissan leaf cells on the way to convert it to LiIon http://www.eco-aesc-lb.com/en/product/liion_ev/ which will boost it from 30amp/hr to about 60!! I want to get the existing cells up to 100V+ to check out the charger/Motor controller/motor etc before fitting my super new cells!!


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    #6
    pedronomix
    Closed Accounts Posts: 997 ✭✭✭pedronomix


    Ps I read somewhere that a variable volt and amp dc supply starting at say 60V @ 0.5 amps and then at say 6-8 hour intervals step up the voltage only in 10V increments. this will apparently avoid overheating etc! The issue is such unit costs a few hundred euro!!


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    #7
    spideog7
    Registered Users Posts: 1,230 ✭✭✭spideog7


    So you've a 30Ah battery, so 1A would be 1/30 of that, I'd even say go down to 500mA (0.5A) to be safe.

    So you want a 0.5A constant current source capable of outputting up to 100VDC (and ideally powered off 220VAC). Such a thing is available to purchase, but off the top of my head I'm not sure of an easy way to do it without building something.

    By the way that high of a DC output is lethal so treat it with extreme caution and your output leads will arc to each other too so keep them well separated.

    I'm assuming your Li-Ion will have ample pack protection but use even more caution with those, they burn mighty hot!!

    EDIT: Yea, you could slowly increment the voltage but that's crude and it can be hard to get right as the batteries ramp pretty fast at that voltage. The power supply you mention likely has a current limit function built in so once you set the current limit it basically becomes a constant current source.


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    #8
    pedronomix
    Closed Accounts Posts: 997 ✭✭✭pedronomix


    OK, I am still with you, surprise surprise!! .... just one sambo short of a picnic. I have seen some suggestions that heavyweight RC ( radio control) bods may have some solutions but my cells are layered 3 deep, so not easy to pick 'em off in smaller bunches


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    #9
    DublinDilbert
    Registered Users Posts: 5,367 ✭✭✭DublinDilbert


    Have a look at what people are doing for conditioning the batteries in the Honda Hybrid's. They are stringing together a number of power supplies (eg 2 x 48V) and a constant current driver for LED lighting, to give a constant current based charger.

    http://ecomodder.com/forum/showthread.php/trollinsight-modding-thread-2000-honda-insight-25785-12.html


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