Another power tank question

[Thom]

Just a quick one - my powertank has finally given up the ghost, after many years service.  It's one of the Maplin jump starter ones.  The battery is not holding any charge at all.

Eventually, I will replace it, but I just need something to see me past Christmas and January's pay packet.  I only use it to draw a very small current - a motor drive for my RA and a HightecAstro DC Focus Controller.  the motor drive only pulls about 1 amp an hour and the focuser is not used a great deal, once focus is found.

My question is, would it be okay to run these items from the powertank when it is plugged into the mains?  For the next few weeks, I'll only be setting up in the back garden, so I can run an extension lead out.  I don't want to go to all the faff of changing the cigarette lighter attachments, only to change them back in the future!

Thanks in advance.

[ronin]

With it plugged into mains the voltage at the terminals will be higher then the standard output, so what is seen at the motors will be higher as well. A lead acid battery outputs around 12v but the charging voltage will be higher, I think the car OP is 12v but with engine running (alternator charging everything) it is 13.4v on my car. I guess the mains charger is similar.

[Vox45]

As a side note, you could look at Deep Cycle Marine Batteries for your replacement battery as they are more suitable for slow discharge than a jump starter.

Some may disagree of course

[Thom]

Thanks Vox 45 but I'm not sure it's worth the expense. I draw so little power that a standard jump starter can last me 12 - 13 hours. Even not holding a charge, this 'dead one' will still power the mount for over two hours! As it cost me £15 about 7 years ago, I call that value for money! If I can find another second hand one...

Sent from my GT-I9505 using Tapatalk

[Physopto]

Hi Thom,

Just for info, a car alternator will output up to about 14.4 volts when charging. It takes a few seconds after first starting the engine, some times you have to rev the engine to simulate moving up through the gears on a drive off. Then will attempt to charge the battery above its nominal voltage. Lead acid batteries are approx. (depends upon make and type) 12.8 volts fully charged 12.4 volts half charge and just over 10 volts absolutely discharged. If a battery is fully discharged it will take time for the battery voltage under charge to reach 14.4 volts. So if you monitor the voltage over time you will see it rise from about the discharged state quite quickly at first then slow down as it becomes more charged. Smart chargers will test the battery before the charge and after it reaches full charge will reduce the charge voltage to about 13.6 volts, maintenance rate. The power tank batteries are I believe gel batteries. Their charging rates should be no more than 10% of the total capacity at any time as the gel can be forced off the plates i.e. a bubble of hydrogen gas is formed. This is the end of the battery as the bubble never dissipates completely. As a general rule of thumb any charging voltage below 13.6 will not generate Hydrogen gas. This is why caravan chargers are normally set at that voltage. Unfortunately not being charged fully to the correct voltage causes them to fail prematurely. ( done for safety reasons). 

Be careful as a lot of so called 12 volt astro equipment is not rated for 14.4 volts and can fail.

Regards,

Dererk

[Bizibilder]

Thom - just measure the battery in your Jump starter for size and note its capacity (in AHr or Amp-Hours).  You will almost certainly find a replacement on somewhere like Amazon or even fleabay that can be swapped in at much less cost than a new replacement.