B2B, mains smart chargers and inverters

Discussion in 'Tech/Mech General' started by cmcardle75, Jun 1, 2014.

  1. cmcardle75

    cmcardle75 Read Only Funster

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    It seems to me that the sort of decent B2B chargers I lust after are about £250 quid, which is a bit steep for the likes of me, especially given my 12V system is currently solar only (mains and engine chargers currently defunct).

    However, a reasonable 7 stage mains charger appears to be about £60, and a good quality 300W inverter to run it costs about £50. For this, compared to a B2B charger, you can get a mains charger for free if you add about £20 of automatic switching. Why shouldn't I just run a mains charger off an inverter instead of spending a fortune on a B2B. (by the way, this is a trick question, as I am a qualified electronic engineer, and understand that the question is ultimately economic in that inverters and mains chargers are mainstream, and hence cheap, whilst a B2B charger is only sought by the few, hence grossly overpriced).
     
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  2. jonandshell

    jonandshell Funster

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    No commercially available mains charger that I know of, within that budget, will bulk charge at the correct voltage for open lead acid batteries!
    To do it properly, you are stuck with a B2B, A2B or an expensive mains charger, thus defeating the object of the exercise.
    BTW, even the 50Amp B2B from Sterling consumes over 600w of 12 volt power. To achieve the same output from a mains charger, a bigger, more expensive inverter is required!

    Good theory, but bigger components are required!:BigGrin:
     
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  3. Wildman

    Wildman Read Only Funster

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    mains charger off an inverter, perpetual motion, hee hee. Trick question as you stated.
     
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  4. Jim

    Jim Ringleader

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    I have a 110ah battery in the trade stand. I charged it today with a mains powered Ctek MXS5 charger powered by my inverter via 2 x 110ah batteries, who were kept fully charged by 360 watts of solar panel on the roof:Smile:
     
  5. TheBig1

    TheBig1 Funster Life Member

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    if you mean to power an inverter and charger from the engine alternator and battery, why not fit a second alternator to charge the leisure batteries direct? would be even cheaper if you used a second hand alternator. quite a few vehicles like ambulances have twin alternators for fast charging
     
  6. cmcardle75

    cmcardle75 Read Only Funster

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    I want smart charging on the leisure battery. An alternator doesn't really cut it. Also, you're talking well more than the 100 quid required for a mains charger and inverter.
     
  7. cmcardle75

    cmcardle75 Read Only Funster

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    Not quite. The inverter is off the engine battery. The charger is on the leisure battery.
     
  8. cmcardle75

    cmcardle75 Read Only Funster

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    I don't know what you mean by the correct voltage for bulk charge. Most of the cheaper mains smart chargers are wet lead acid only, rather than the other way round and will bulk charge at constant current, not voltage.

    Besides, I don't need a 50A charger. Around 15-20A will be just fine. I've only got a 180Ah battery, so that will recover from 50% to 100% in about 5 hours, which given I do a lot of driving, the battery lasts days without charging and I have solar as well, will be perfectly acceptable.

    Also, my alternator is only 60A and I still need to run the headlights, wipers etc.

    Also, if I went with a B2B, I'd still need to buy a mains charger anyway. Yes, that would be more convenient than switching the source, but I don't care, I'm rarely on mains and won't mind flicking a switch or moving a plug from one socket to another.
     
  9. jonandshell

    jonandshell Funster

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    Of course, your proposed setup could also flatten your engine battery.

    It is entirely possible that with your road lighting on, your heater fan running and your new improvised charging system on the go, that you could be drawing more amps than your alternator can produce! This will result in a flat starter battery due to the shortfall in alternator output. Your invertor will keep going regardless until your starter battery is down to 10.5 volts!

    'Proper' B2B and A2B chargers monitor the starter battery.

    Correct bulk charging voltage for an open lead acid battery is 2.5 volts per cell. In the case of a 12 volt battery, it should be 15 volts. However, Sterling are brave enough to go to 14.8 volts.

    Automotive alternator regulators limit voltage to 14.4 volts to minimise gassing and water usage in unmaintainable sealed batteries.
     
  10. cmcardle75

    cmcardle75 Read Only Funster

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    Indeed some B2B chargers are known to have this problem. One easily solved if your inverter has a low voltage protection system, or by using a split charge relay to feed it if it doesn't.
     
  11. DABurleigh

    DABurleigh Funster

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    I've thought long and hard on B2Bs over the years. For the average motorhomer, I'd say ensuring you have thick (doubled-up is easier) cables between alternator and leisure batteries is generally a better way to go. Cheaper, KISS philosophy, less risk of curtailing the life of the leisure batteries with voltages above the gassing voltage. The price you pay is not quite as much energy stored in the leisure batteries once charged. If that is so valuable to you, then consider another or a bigger battery.

    If you look at charging rates WITH decent cabling, when the leisure batteries are low the alternator is capable of shoving in as much as (and occasionally more than) a ~45A ouput B2B . When the batteries are approaching anywhere near as full as a vehicle battery (14.4 max from alternator) the charging current is lowish even with a B2B, and it is only in the mid-depletion region the B2B can offer much of an improvement.

    This last case may be useful if you are touring daily short distances off-EHU in the cooler months (when solar struggles) but generally, I would say put a little effort into maximising the charge current at the leisure batteries in preference to an expensive B2B.

    Dave
     
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  12. jonandshell

    jonandshell Funster

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    All well and good, by all means save a few quid on your charging circuit.

    You will pay for it with recurrent battery renewal though! An alternator regulator offers only a compromise between a reasonable charge time and a reduced voltage to avoid contant overcharging.
    Only a B2B or A2B charger provides a correct charge cycle and floating voltage.

    Our batteries have been rapid charged by a Sterling product from new.
    They are 6 years old and still have full capacity. That cant be said of ANY battery maintained by a standard split charge and alternator regulator.
     
  13. dave newell lvs

    dave newell lvs Trader-Vehicle Services

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    If its of any interest/use I have two old stock but brand new CTEK B2B chargers available, the older D250S not the Dual. One is boxed with instructions the other is an ex display unit with no box or instructions, boxed unit is yours for £130 plus P&P @ £7 the unboxed unit is yours for £100 plus P&P @ £7. Call us if interested.

    D.
     
  14. cmcardle75

    cmcardle75 Read Only Funster

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    PM sent, but not sure if it worked...
     
  15. dave newell lvs

    dave newell lvs Trader-Vehicle Services

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    Yes both worked, pm sent in reply, phone us tomorrow during normal working hours on 01952 587702.

    Cheers, D.
     
  16. dave newell lvs

    dave newell lvs Trader-Vehicle Services

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    charger posted 1st class to be signed for this lunchtime so you should have it tomorrow or Thursday.

    D.
     
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