12v or 15v adapters for 12v SLA Battery ?

[Furkin]

Hi,
I need to replace the switching power adapters for TWO Car Booster/Starters.
They are very similar units (s'posed to be the same) with the same: 12v 17ah SLA batteries.

One has a UK adapter of 12v - 500ma.
The other has a Euro 2-pin adapter of 15v - 1000ma.
I was going to get a 2-pin to UK 3-pin adapter, but for the same money can get a new adapter.

My question is:
Which is the better size (12v/500ma :: 15v/1000ma) adapter for this purpose ?

I've only ever seen 12v items before, so am wondering if the 15v was a mistake.
Its a new (!?) Blackspur Booster, so it could be absolutely anything. Pride & service isn't their strong point.

IF 15v is better - i'll get 2 of 'em.
If its wrong, i'll get 2 12v items.

Thanks for reading

 

[Spark123]

iirc to trickle charge a 12 SLA battery you need somewhere around a 13.5v charger. For a quicker charge a slightly higher voltage is needed and will take a bit more current.
Can you not buy the specific adaptor for the appliance?

 

[ericmark]

The float charge voltage for lead acid is 13.2 volt and the open circuit voltage for a RB106 Lucas voltage regulator for a 12 volt battery is 16 volt.

So the peak voltage needs to be some where between the two. Maybe even up to 18 volt. However the RMS value can be lower.

The power supply relies on the volts dropping and it is rather a hit and miss thing so if heavy use the the larger one will be best but for light use the smaller one is best as less likely to over charge battery.

 

[Mursal]

15Volts @ 1A will be the best, probably an internal regulator in the charger anyway.

 

[Furkin]

Thanks folks - you always come up with the goods.

"Can you not buy the specific adaptor for the appliance?"
As in my OP, thats the bit that threw me.
Two similar appliances came with different chargers.

As far as actual 'use' is concerned, they won't be used a great deal - hopefully. Its more a matter of keeping them up to charge,,,, ready for emergency time.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In the meantime, does anyone know where I can get a 12v 10ah/20hr SLA battery sized; 151x110x65cm - with terminals at seperate ends please ? Physical size is important as it needs to fit an actual space.

thanks again

 

[EFLImpudence]

Google or Cornwall Battery Centre ?

 

[Mursal]

Just be careful of the postage, as you probably already know.

http://www.ebay.ie/sch/i.html?_from=R40&_trksid=m570&_nkw=sla+battery

Happy Christmas

 

[Furkin]

GOOGLE / E-BAY / CBC ?!
ahhhh,,,,, if only it was that simple.

I have been searching,,,, but it looks like as soon as I got one, the supplier/manufacturer disappeared !
Actually it’s a Steyre – Ning Bo Bei Kang Dian Zi You Xian Gong Si (Ningbo Becam Electronics Co., Ltd) - & I know they are still manufacturing. I did drop them a line some weeks ago, but no reply.

I find one with the right figures, but wouldn’t fit the space.

I found another one at the right physical size: that had a different ah/hr figures. The supplier couldn’t help me in whether it would suit or not (understandably covering his back).

I seem to recall finding something similar, but with both terminals at the same end – which I dismissed at the time. It would have meant looking for a piece of the correct cable, to extend either black or red. That one looks quite acceptable now,,,, if only I could find it again.

Right – I’m off to search for Cornwall Battery Centre.

Wishing you all:
A fabulous & peaceful
New Year

 

[ericmark]

With a smooth DC supply 13.2 is considered as the float charge voltage. That's the voltage required to hold the battery in readiness for use without drying out the electrolyte.

After use a higher voltage is used to recharge often as high as 14.8 volt but the current is carefully monitored and once it reaches a set limit the charger will lower the voltage.

Clearly this can't be done with a cheap plug in the wall charger so it works on a compromise. Using a rectified AC you have a wave form which can average as low as 10 volt but has a peak voltage of 14 volt so on the peaks will charge the battery even though a meter which measures RMS voltage shows the voltage to be too low.

So you can measure the output from a power supply at 12 volt. Measure the battery voltage at 12.8 volt connect the power supply to the battery and see the voltage rise to 13 volt which is all due to measuring RMS value with the meter.

This works out well as the sine wave means it charges when it reaches the voltage mark then has a space before it starts to charge again and the mark naturally becomes shorter and the space longer as the battery voltage rises.

So in the main you can use any non regulated DC power supply of around 11 to 13 volt as long as it does not overheat the power supply. If you measure the voltage of the battery on charge at 13.8 to 14.2 volt if would be considered charged and I would not charge 24/7 but charge once every two weeks to replenish natural losses.

So where not used much the lower rated charger will be better as you can leave it on charge for longer may even be able to leave on charge 24/7 without damage to battery. But were used a lot the larger charger would work better getting the battery re-charged quicker. But likely you will find the instructions vary one saying charge for X hours the other saying leave on charge 24/7. With different instructions both power supplies would match the same unit.

 

[SimonH2]

As already hinted at, you absolutely cannot just pick some random power supply. A 12V regulated charger will not charge a 12V LA battery, a 15V one with either fail or destroy the battery.

My experience is that most "budget" VRLA battery containing equipment doesn't include a charger circuit. It'll come with some cheap PSU that is chosen to "sort of" provide about the right voltage/current capacity to charge the battery - probably relying on the output voltage dropping with current to limit charging current.

To charge a VRLA (aka Sealed Lead Acid (SLA), or "dryfit") properly needs a multi-stage charger roughly matched to the capacity of the battery. If the charger is too small then it won't fully charge as it'll switch from "top up" to float mode too soon. If it is too large then it might not switch out of "top up" mode and will dry out your battery in a few hours. Most VRLA batteries are specced to float at 13.2 to 13.5, or float (trickle) charge at up to 13.8V. Above than and they'll start to gas too much and you'll dry them out. At opnly 13.2V then you might never reach 100% charge.

Complicated isn't it ?

So these "budget" units rely on the user not leaving them plugged in too much, and them lasting long enough to avoid warranty complaints. Once the warranty is over then it's not their problem that their cheap design has killed the battery. It's a common comment that “VRLA batteries don't die – they're murdered.”

A quick look on fleabay shows that most automatic chargers seem to start at around £30. Such as this [/url=http://www.ebay.co.uk/itm/3-STAGE-BATTERY-CHARGER-MAINTAINER-6-VOLT-12-VOLT-2-7-amp-SWITCHED-6V-12V-/270987815122]Durite unit[/url]. Most on there give so little information that it's impossible to make an informed decision as to suitability. And given that some vendors don't seem to know the difference between "Amp" and "AmpHour" you can't really expect to get any help from them

 

[ericmark]

You are of course right a three stage charger or better still a pulse charger would do a really good job but is a bit of over kill.

A transformer, full wave rectifier, smoothing capacitor, fuse, 7812 voltage regulator and a red LED is what most regulated chargers use.

The red LED on the common of the 7812 both raises the voltage to 13.2 and gives indication that it's charging.

The cheap plug in battery replacement non regulated unit could easy be converted to do this by adding a capacitor, fuse 7812 voltage reg and red LED. However I would assume the guy is not looking to make his own.

These components could be fitted inside the main unit. But in real terms it is not really likely we can guide him on how to either check what he has or build a unit.

However at radio rallies I have bought these all ready made designed to maintain a car battery where left for an extended time without use.

these are not the best option but good enough to charge the cheap unit he has.

 

[Furkin]

yep - you've hit the nail right on the head.

The cause of the charger/booster unit problems has been battery failure.

Along with crap service, it looks like Blackspur cause their own problems by supplying the wrong charger/adapters.

Who'd have thought that a little thing like a charger/adapter would be so complicated - to Joe or Josephine Public ?

Thanks all for your help - i'll keep it on file, as I'm sure i'll need to refer to it again.

all the best