1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

How long for battery to charge?

Discussion in 'General Cars' started by fitzykev, 17 May 2020.

  1. fitzykev

    fitzykev

    Joined:
    13 Apr 2011
    Messages:
    92
    Thanks Received:
    1
    Location:
    Antrim
    Country:
    United Kingdom
    Hi all. If it takes a 52ah battery 10 hours to charge how long will it take a 35ah battery to charge?
     
  2. Harry Bloomfield

    Harry Bloomfield

    Joined:
    30 Dec 2018
    Messages:
    2,268
    Thanks Received:
    288
    Country:
    United Kingdom
    Its not a certainty to calculate with so many variables, but I would suggest around 7 or 8 hours.
     
  3. fitzykev

    fitzykev

    Joined:
    13 Apr 2011
    Messages:
    92
    Thanks Received:
    1
    Location:
    Antrim
    Country:
    United Kingdom
    No problem. It's a 4amp 12 volt charger if that helps?
     
  4. Harry Bloomfield

    Harry Bloomfield

    Joined:
    30 Dec 2018
    Messages:
    2,268
    Thanks Received:
    288
    Country:
    United Kingdom
    4amp might be the initial charge, but it will rapidly decline as the battery charges, hence difficult to give an exact time. Battary condition also has a bearing on it too.
     
    • Thanks Thanks x 1
  5. fitzykev

    fitzykev

    Joined:
    13 Apr 2011
    Messages:
    92
    Thanks Received:
    1
    Location:
    Antrim
    Country:
    United Kingdom
    I would say the battery is about 5 years old
     
  6. Sponsored Links
  7. Harry Bloomfield

    Harry Bloomfield

    Joined:
    30 Dec 2018
    Messages:
    2,268
    Thanks Received:
    288
    Country:
    United Kingdom
    A 5 year old might be like new, a six month old might have been abused. Put it on charge and wait whilst the 'charged' LED comes on, on the charger, then let us all know how long it took.
     
  8. bernardgreen

    bernardgreen

    Joined:
    3 Nov 2006
    Messages:
    22,709
    Thanks Received:
    2,138
    Location:
    Bedfordshire
    Country:
    United Kingdom
    how flat was it ( is it ) before you start to charge it ?
     
  9. festive

    festive

    Joined:
    31 Aug 2005
    Messages:
    2,800
    Thanks Received:
    154
    Country:
    United Kingdom
    One of my older cars had an almost flat battery, using a CTEK 5amp took it a good 12-20hrs to charge and recondition.
     
  10. Harry Bloomfield

    Harry Bloomfield

    Joined:
    30 Dec 2018
    Messages:
    2,268
    Thanks Received:
    288
    Country:
    United Kingdom
    Quite right. My battery is an 80amp and I use a similar intelligent charger to the CTEK, rated I think 4.5a. It needs at least 24 hours to bring it back up to a full charge when its low. My charger might be rated 4.5a, but the current rapidly drops to below 1a as the battery begins to rise in voltage. The only way to more rapidly charge, is by increasing the output volts of the charger.

    The difference in voltage between a flat battery on charge and one which is fully charged, is just a fraction of a volt.

    I dumped all of my old fashioned uncontrolled, battery wrecking chargers long ago. The only way to check progress with those, was to watch the battery for gassing. Modern batteries are sealed, so just no way to observe the gassing. Leave them gassing too long and the battery was ruined.

    Modern chargers can just be connected and left to it, with no risk of damage if they are forgotten about for an extra day or two, but if left permanently on charge, they are still quite capable of ruining a battery. I used to store my caravan in my drive, with its battery always on charge at 13.8v from its built in SMPSU. Two years of this treatment and it was ruined. My present regime is to put the battery on the 13.8v every month or two, for a couple of days at a time. Between times, it is isolated. When I intend to use it, I connect a CTEK type charger and bring it up to a full charge - I need a good battery for the caravan mover.
     
    • Like Like x 1
  11. ericmark

    ericmark

    Joined:
    27 Jan 2008
    Messages:
    15,217
    Thanks Received:
    1,361
    Location:
    Llanfair Caereinion, Nr Welshpool
    Country:
    United Kingdom
    10 hours.
    Yes I know it seems daft but time is the main factor not charge rate. So with any lead acid battery as it discharges the sulphuric acid is turned into water and sulphur, and the sulphur is deposited on the battery plates, the longer the sulphur stays on the plates the harder it gets, so if you discharge a battery 20% and start the recharge one minute latter, then in one hour the battery is likely charged, but if you wait 8 hours then start to recharge then likely 10 hours, wait a month and likely will take a week to recharge.

    It is not how fast the charger is, but how fast the battery will accept the charge. OK there are ways to recharge batteries faster, with a flooded lead acid (that means you can top up the electrolyte with distilled water) you can use a stage charger or a pulse charger to recharge the battery fast, but with a sealed battery valve regulated lead acid (VRLA) or absorbed glass mat (AGM) the charge rate needs to be carefully controlled.

    With a 90 Ah battery using a smart charger rated 3.8 amp likely it will only charge at 3.8 amp for ½ hour, after which it will charge at a lower rate, and with a 35 Ah battery using a smart charger rated 3.8 amp likely it will only charge at 3.8 amp for ¼ hour, after which it will charge at a lower rate, so the difference in charge time is ¼ hour between the two batteries.

    This charge22-4-20.jpg is typical of the charge pattern from a battery charged with a smart charger, you will note a very short time being charged at 3.8 amp = approx 58 watts, the meter measures watts the charger is using, then slightly longer at 3 amp = 52 watts, with the charge rate at 0.8 amp = 12 watts not being completed, it would have in fullness of time dropped to 0.1 amp and finally off.

    Because most of the time the charge rate is very low, time to charge is rather long, this is why lead acid is not suitable for most electric vehicles, it was OK for fork lifts, milk floats, mobility scooters all always recharged at their base and used for less than 8 hours a day. But for cars, push bikes, etc, what the battery both light as possible, and ability to fast charge.

    The AGM or VRLA can charge faster than flooded, but to do so the vehicle has to map the battery and hold the battery at 90% charge for a week but then allow full charge once a week to prevent battery damage, so it can only be done with computer control and with a vehicle in regular use. My wife's car with stop start with the lock down has required the battery to be recharged with a smart charger as used so little.
     
    Last edited: 3 Jun 2020 at 9:16 AM
Sponsored Links
Loading...

Share This Page