Multi Meter reading for transformers

[Furkin]

I have a Car Battery Booster that I'm trying to charge up, but it's struggling to get up to voltage. Actually I'm not sure whether this should be 12vdc or 14vdc - as per vehicle electrics - but I'll leave that bit for the moment.

I tried to test the transformer with my multi-tester, but couldn't get a proper reading.
Ignoring the actual application at the moment, what reading should I be getting when testing the output from a (any) AC to DC transformer ? The one that came with it - that I'm testing - is rated at 15v 500Ma.

When I test it at the barrel (20vdc on tester - centre pin +), I get a 1.
I initially assumed that it was faulty & was looking for a replacement. The Booster says it needs a 12vdc input.

I tested another transformer from my home phone, & that likewise gives me a similar reading. This is fully functioning, as it's used all the time on my phone.
So - now I don't think there is a problem with the transformers. I think the problem is with the user not understanding electronics. I assumed it would read 12vdc (or 14vdc).

2/ If I do get another transformer, should I:
a) get a similar 15v 500Ma ?
b) get a 12v 500Ma ?
c) would a different Ma size help the charge in this instance &/or help the lifespan of a transformer ?

many thanks for reading this.

 

[1john]

sounds like a duff meter. the transformer rating is printed or stamped on the transformer.

 

[Furkin]

Many thanks John,

My Son has a similar (different brand) meter that I bought him,,,, i'll get him to pop over with it.

In the mean time - Can I test the meter in some way ?

It seems to read everything else (batteries / household sockets / car stuff etc) o.k.

 

[TheOriginalTonkaToy]

If you're getting a 1 try changing the meter range to the next higher DC range.

 

[TicklyT]

Is output of the power supply you are testing AC or DC? AC supplies may be marked 'AC' or with a '~' symbol, DC power supplies with 'DC' or '-.-.-.'

The '1' display on your meter may be indicating it is seeing a voltage outside the range you have selected.

With no load connected, the open circuit voltage of transformers drifts up above their normal working range. I would not be surprised if it went up to something around 25 Volts. Try a different range on your meter, say a 100 or 200 Volt range.

More satisfactory results would come from testing the output voltage whilst the transformer is connected to a load of somewhere around it's rated capacity. For your transformer, connecting it to a 12 Volt 5 Watt lamp would be about right. In fact, If the lamp lights up nice and bright, there's probably llittle wrong with the transformer part of the power supply, and you can use your meter to establish if the internal rectifier of a DC power supply is functioning.

If your 'transformer' turns out to be a switched mode power supply, then all bets are off. They often just shut themselves down and sulk, giving no output unless they are correctly connected to the load they are intended to feed.

 

[Furkin]

many thanks guys,
For 90% of my use, I use 20vdc on the m.tester, as i'd be testing car stuff, batteries etc.
The next setting is 200vdc, which I did try. I can't now recall whether it read 1 or 0.1,,, but it didn't bring up a proper reading.
Sorry TT: my initial draft did say the output was 15vDC (got lost in the re-write/s !).

Switched mode: I have no idea. It's a 'basic' 3-pin plug in type that came with the booster.
//media.diynot.com/60000_59077_17044_35938005_thumb.jpg
I assume that I'm using the image up-loader wrong,,,, as well !
Whilst I don't mind looking inside things, this unit is sealed/moulded, so I don't think I can check the insides, without bu@@ering it up.


If the Transformer is shot - i'll get another.
If the Tester is shot - i'll get another.
If the Booster is shot - i'll have to think about it,,,,

but I need to know which.

My son is bringing his meter over shortly & I'm looking for a 12v bulb to test as advised.

Will update a,s,a,p.

 

[TheOriginalTonkaToy]

The weight of the unit is usually an indicator of PSU type. Switched mode types are very light and have safety circuits that shut them down in the event of a fault either in the supply itself or the load. If the meter you're using is a digital type, then it's likely that the PSU is seeing it as an open circuit meaning that if it's a switched mode power supply it might just shut down. As Ticklyt said, loading it with a suitable lamp should prove whether it's working or not.

 

[Furkin]

UPDATE:
Transformer:
I've now tested it with 3 Multi Testers, & it always comes up reading 1.
I have tested 3 other transformers, with 3 testers, & they all come up reading 1 on all meters.
I put a 12v car bulb to the original transformer, & it lit up very bright & got very hot (remember - this T/F is 15v) I tried the bulb on the other T/F & it lit 'as normal'.

Meter:
I've 'tested' the meter on dozens of other things (along with the other two meters) & everything seems to work o.k.

This leads me to think that the transformer & meter are working well.

Booster:
The booster has taken about 11.60 volts (as tested at the 'battery leads')
Should this read 12v for vehicle use,,,, or 14v ?
When I test it with the transformer 'charging' it reads just about 11.85/11.99 v.

With my limited knowledge of these things, I now suspect that the booster its-self is faulty. (I still don't mind being proven wrong).
It hasn't been charged for a few days now, but has held the charge that it did get up to.

It has a small inverter (100w) on it, into which I have plugged a light-bulb & couple of radio's, all of which seem to work alright.

I am now guessing (through these bits of elimination) that the booster isn't taking the charge,,,, but will hold it once it does.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It's unusable as it is, so I want to take it apart & see if I can fix the input charge side. It's well out of warranty

I really would appreciate it if someone has the time - and inclination - to help me in this.
Obviously I absolve anyone from blame if things go wrong,,,,,, the booster is already bu@@ered, so it can't get worse.

Incidentally, it's a Blackspur (not the best of brands I admit). I don't have the model number to hand, but it's the big Yellow one, with Inverter, lights, 12v outlets & compressor etc.
I am a disabled gent, & this really is only used for emergencies,,, (so far - mainly for other people) but it would be nice to think that it is still usable when it needs to be.

I'd like to think that some diode or capacitor is failing and that it can be sorted.

Any takers please ?

Thanks for reading this.

 

[ban-all-sheds]

UPDATE:
Transformer: .....

Tested and found to be working

Booster:
The booster has taken about 11.60 volts

So not completely dead.

When I test it with the transformer 'charging' it reads just about 11.85/11.99 v.

So it is being charged by the charger.

It has a small inverter (100w) on it, into which I have plugged a light-bulb & couple of radio's, all of which seem to work alright

So it's working well enough to power an inverter.

,,,, the booster is already bu@@ered, so it can't get worse.

It's not, and therefore it can.

I'd like to think that some diode or capacitor is failing

Or a resistor, or a transistor, or an inductor, or an op-amp, or an oscillator, or... or... or...

and that it can be sorted.

Do you have the tools and knowledge to trace and identify faults in electronic circuits?


IMO a very likely root cause is simply that the SLA battery/ies are on the way out. How old are they? How often do you charge them? Where do you keep the item? Can it be opened up so that the battery can be replaced? What's the cost of replacing the battery compared to buying a new booster?

 

[Furkin]

many thanks BAS:
As you say, it's not all 'dead', but unusable - 'as is'.
That's why I'm willing to have a go at fixing it.

No - I'm not an expert, or an electrician (tho' I did start out as an apprentice,,, but on underground HT stuff - another matter).
Having said that, I am not totally green: having run my own business selling & installing CCTV & similar equipment, have built LED lighting/chasing & controllers, fixed other electronic goods over the years, been a life long fan of gadgets and electronics, might have a bit more knowledge than Joe Average.
I have replaced similar components before, but do need help in locating the problem. Hence my quest for help on these pages. If I knew it all, I'd be getting on with it instead of bothering you guys - of which I have the greatest of admiration.

Thanks also for your comments on SLA Battery.
At this moment, I have not opened the unit. I will look for said batteries and check them.
The unit is usually left in a charged state – ready for use. I discharge it once a year then charge it again, in readiness. It’s kept in my spare bedroom.

cheers

 

[ban-all-sheds]

Do you mean kept permanently on charge?

What do the instructions say about a charging/maintaining/discharging routine?

 

[Furkin]

Sorry - not 'On' charge,,,, but 'In' charge (charged state) - ready to use.

The instructions have long gone,,,, (don't know why or where cos I usually save such things, & have them going back 10/15/20 years)

I always like to discharge rechargeable batteries every now & then, depending on what it is & how often used etc.

 

[bernardgreen]

Booster:
The booster has taken about 11.60 volts (as tested at the 'battery leads')
Should this read 12v for vehicle use,,,, or 14v ?
When I test it with the transformer 'charging' it reads just about 11.85/11.99 v

11.60v on the battery that increases to 11.85v when the charger is turned on suggests two things

[1] the charger is a constant current charger putting a set current through the battery and not a simple voltage source letting the battery take as much current as it wants to.

[2] that one cell of the battery has partially failed. Depending on the type of cell a fully charged 6 cell battery will be around 14 volts. 2.3 volts per cell.

Therefor one dead cell that is still conductive will allow the charging current ( and discharge current ) to pass as if a near zero ohm resistance but leaves only 5 cells with charge and voltage.

5 times 2.3v = 11.5 volts on the battery terminals

 

[ban-all-sheds]

Sorry - not 'On' charge,,,, but 'In' charge (charged state) - ready to use.

A year between charging the thing is probably far too long.

In the absence of a proper instruction manual try every 2-3 months.

 

[Furkin]

Have now got the thing apart.
The first thing that I noticed was that the Pos/Red lead onto the + battery terminal wasn't tight. This could be the whole problem.

I have put the SLA battery on charge to see:
a/ if it takes a charge
b/ if it holds a charge.
This will show or eliminate battery problems.

Looking at the charging board in the unit, if a component is blown/on its way out on that, I don't think I could swap it.
If the problem is there, I'll need a replacement board,,, which I don't think Blackspur would supply !
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"A year between charging the thing is probably far too long. In the absence of a proper instruction manual try every 2-3 months."

Would you advise to fully discharge each time ?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Thanks so far guys.