Car Jumpstarter Question
Discussion
Hey all,
Just got a new £35 jumpstarter thing from Maplins with built-in air compressor.
Just a question - the battery was completely flat when opening the box. The battery level indicator did not light up when pressing the "test" button, and none of the functions worked. So I hooked it up to the power point on my wall to charge it (using a supplied AC/DC adapter), and tested it about five minutes into the charge. The indicator lights showed a full charge (which surprised me).
The manual says to charge it until it shows a full charge. So I thought, great. I tested it, and sure enough, there is not enough juice to power the compressor for more than a minute before running flat again.
Within ten secons of plugging the device back into the wall, the battery indicator once again shows "full", and when I hook up a separate battery level tester to the clamps, it's reading 13.5 volts.
Is it normal to show "full" almost immediately upon plugging it into the wall?
Thanks!
Just got a new £35 jumpstarter thing from Maplins with built-in air compressor.
Just a question - the battery was completely flat when opening the box. The battery level indicator did not light up when pressing the "test" button, and none of the functions worked. So I hooked it up to the power point on my wall to charge it (using a supplied AC/DC adapter), and tested it about five minutes into the charge. The indicator lights showed a full charge (which surprised me).
The manual says to charge it until it shows a full charge. So I thought, great. I tested it, and sure enough, there is not enough juice to power the compressor for more than a minute before running flat again.
Within ten secons of plugging the device back into the wall, the battery indicator once again shows "full", and when I hook up a separate battery level tester to the clamps, it's reading 13.5 volts.
Is it normal to show "full" almost immediately upon plugging it into the wall?
Thanks!
Ah, but the rub is that I'm in Malaysia. 
A friend shipped it over with his stuff when he moved house a couple of months ago.
I'm just wondering whether leaving it plugged into the wall for a couple of days is the way to go (and that the battery level indicator doesn't mean anything), or whether I should go out and get a replacement battery for it.
Devices like these are not available here (even if they were, they would cost more than £35 and the cost of a new battery combined), so even if I have to shell out for a replacement battery for it, I will.
So what I'm looking for really is a conclusive answer from someone who understands the technicalities of these things. Is the voltage output of the battery (and thus, the level indicator) supposed to rise gradually as a healthy battery is charged from near-flat, or does it immediately show a high voltage, but just perhaps not be able to supply a strong current?
A friend shipped it over with his stuff when he moved house a couple of months ago.I'm just wondering whether leaving it plugged into the wall for a couple of days is the way to go (and that the battery level indicator doesn't mean anything), or whether I should go out and get a replacement battery for it.
Devices like these are not available here (even if they were, they would cost more than £35 and the cost of a new battery combined), so even if I have to shell out for a replacement battery for it, I will.
So what I'm looking for really is a conclusive answer from someone who understands the technicalities of these things. Is the voltage output of the battery (and thus, the level indicator) supposed to rise gradually as a healthy battery is charged from near-flat, or does it immediately show a high voltage, but just perhaps not be able to supply a strong current?
Edited by -DeaDLocK- on Thursday 11th November 11:16
I've got one of these, but not a maplin version. Seem to remember that it was completely flat when I first got it and had similar charging experiences. It certainly needs a full charge overnight to have any chance of supplying enough grunt to get the MG B to turnover, yet the indicator shows full voltage after a few minutes charging.
-DeaDLocK- said:
Two separate devices (multimeter and battery tester) both confirm 12.5v output. This correlates with built-in battery indicator.
Is voltage a reliable indication of charge?
The process of charging raises the voltage of a cell, often higher than the maximum 'rest' voltage that one would expect from the cell when it's fully charged.Is voltage a reliable indication of charge?
When charging has ceased, it takes a little while to settle back down to rest voltage, which is no doubt what the charge indicator is calibrated to.
I suspect that you're measuring the voltage before the battery has settled, let it sit for half an hour or so to get an accurate reading.
Edited by The Wookie on Thursday 11th November 11:36
-DeaDLocK- said:
Two separate devices (multimeter and battery tester) both confirm 12.5v output. This correlates with built-in battery indicator.
Is voltage a reliable indication of charge?
A battery nominally has 6 cells of 2.2v. Therefore a fully charged, brand-new battery should read 13.2v straight off the charger. In theory. In practice, because of internal resistance which starts to build inside the battery from day one, the voltage is likely to be nearer 12.8 - 13.0 Is voltage a reliable indication of charge?
Static voltage is, however, not a good indicator. Voltage under load is a better indicator, but still does not easily differentiate between a poorly-charged battery and a knackered one.
As already recommended, put it on charge overnight (at least) and then see how long the compressor runs. Mine is about 10-years old now and can still run the compressor for twenty minutes plus.
If it does need a new battery, I believe that some units use the same battery as used in burglar-alarm systems and these can be had for a good price usually.
You and the guage are confusing "voltage" and "current".
A lead acid battery will go straight to 12v when it's charged because that's its natural voltage (bar the shouting). However, you can only get out what you've put in and it takes a long charging cycle to get any capacity to deliver heavy current for any worthwhile period of time.
The ONLY way to test a battery properly is with a high current drain discharge tester.
The best DIY way is to have it indoors (for room temperature sensitivity), charge it fully and then leave it to stand overnight. Test the voltage in the morning and you are ideally looking for 12.6v. Anything below 12.4v is a tired battery and 12.2v is a knackered battery.
A lead acid battery will go straight to 12v when it's charged because that's its natural voltage (bar the shouting). However, you can only get out what you've put in and it takes a long charging cycle to get any capacity to deliver heavy current for any worthwhile period of time.
The ONLY way to test a battery properly is with a high current drain discharge tester.
The best DIY way is to have it indoors (for room temperature sensitivity), charge it fully and then leave it to stand overnight. Test the voltage in the morning and you are ideally looking for 12.6v. Anything below 12.4v is a tired battery and 12.2v is a knackered battery.
littleredrooster said:
-DeaDLocK- said:
If it does need a new battery, I believe that some units use the same battery as used in burglar-alarm systems and these can be had for a good price usually.
Yes, they do use the alarm type of battery but when I wanted to replace mine I found that it was cheaper to buy a new jumpstart unit rather than a replacement battery.Have had two of these and every time I needed to use them the internal battery was flat so had to charge it up for a day before I could jump start the car. I now keep a new spare car battery fully charged in the garage and every couple of months use one of the auto-regulated chargers to make sure the charge is at max. Much cheaper and more convenient.
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