Pignose 7-200 Hog 20 - charging/powering

[shortcircuit]

^^^^^same schematic I referenced post #8 from, all apologies for not posting then.

[J M Fahey]

Simplest "practical" charger is a power supply with maximum desired voltage , say 16V which is 100% charge, and with a limiting resistor so when charging a real flat battery (11V or so) current is still within charger capability.
Yet when battery reaches 16VDC current drops almost to zero.

So simplest is a 12VAC transformer, say 1A capability, a diode bridge, a 4700uF capacitor , this supply will give you about 16V unloaded, around 15V loaded; plus a series 5 ohm 10W resistor.
This supply will "just" feed 1A to a flat 11V battery , quickly (a couple minutes ) reaching 12V and from there on taking overnight to charge these alarm type batteries (12V 7AH is the most popular value).
And is probably what Pignose and tons other simple cheap chargers have inside.
Some chargers dispose of the electrolytic capacitor and just use the bridge ... plus the resistor of course, they just take about twice the time to charge because current is not continuous but narrow pulses rectified fullwave.

EDIT: works fine BUT batteries allowed to reach 16V dry up quickly; so user must check voltage now and then , a comparator might turn an "Unplug/overcharge" Led on or user must simply unplug charger after 8 hours.

It is NOT safe to forget charger plugged in more than 8 hours.

So for this Pignose, the charger suggested works fine and is very easy to make, just remember to unplug it.

Later Iīll draw a simple fast yet safe charger, which can be left plugged forever, what I include in my "Callejero" street amps.
Obviously, cheap and simple, you know Iīm a cheap minimalist.

[jondoe]

The schematic above is a little different to the board in mine, quite a few variations in values of components and some missing entirely. Mine is a older open back model, not like the new closed back.

I do have a problem running my guitar through it, when I use the power supply I bought with the guitar it creates huge amounts of hum and buzz if I don't touch the strings, like a ground fault, but it runs perfectly off a battery. But, If i use the PSU with a signal generator from a tablet that works percetly. I suspect maybe the PSU is dog shit as my guitar sounds fine on 4 other amps I have here.

[jondoe]

So, a friend of mine imported a Pignose charger from the states for this particular amplifier and paid through the (pig)nose for the pleasure, but this would surely be the correct 15v pictured device and be perfect for the amp.

Wrong!

The adapter provided by Pignose was not the one shown on their website, it's a more generic looking adapter, with a little Pignose sticker on it and more to the point it has a 12v output. They also failed to send a UK spec 3 pin version, but perhaps they don't have them? To add insult to injury the power supply causes huge amounts of noise, just like all the random 12v supplies I'd tried before.

It still would seem impossible for the 12v adapter to correctly charge the batteries at 12v, so what gives?!

[J M Fahey]

Sorry I thought you had solved it and didnīt continue.

This is my safe/intelligent charger:



* feed it from a cheap 19V (or higher) Laptop Brick.

* It ouputs whatever voltage the battery needs , from very dead 10 or 10.5V (usually shouldnīt be descharged 11.5V on penalty of reduced life) and not higher that 14.4V ... the standard car voltage regulator voltage so we know itīs Industry Standard safe.

You charge battery overnight, say 9 hours for a 12V 7A battery and it will last forever.

You forget to unplug and it gets extra 24 hours? No big deal.

You forget it plugged in for 2 or 4 weeks?

Youīll dry your battery somewhat, suggest opening the tiny rubber capped vents and replace distilled water to normal level; in any case you wonīt murder them by any means, when fully charged current will automatically trickle down to a few mA; you get 1A only when battery really needs nthem, for fastest safest charging.

While a constant 1A current for 2 or 4 weeks will damage it.

Oh, youīll need a small heatsink for the voltage regulator.

If you donīt want to use a laptop brick,use a 16VAC 1 to 2A transformer, a 2 or 3A diode bridge and a 4700uFx25V electrolytic as a primary raw voltage source.

[shortcircuit]

Have you tried plugging the charger in and taking an actual output voltage reading ??

[jondoe]

Sorry I thought you had solved it and didnīt continue.

This is my safe/intelligent charger:

[ATTACH=CONFIG]54582[/ATTACH]

* feed it from a cheap 19V (or higher) Laptop Brick.

* It ouputs whatever voltage the battery needs , from very dead 10 or 10.5V (usually shouldnīt be descharged 11.5V on penalty of reduced life) and not higher that 14.4V ... the standard car voltage regulator voltage so we know itīs Industry Standard safe.

You charge battery overnight, say 9 hours for a 12V 7A battery and it will last forever.

You forget to unplug and it gets extra 24 hours? No big deal.

You forget it plugged in for 2 or 4 weeks?

Youīll dry your battery somewhat, suggest opening the tiny rubber capped vents and replace distilled water to normal level; in any case you wonīt murder them by any means, when fully charged current will automatically trickle down to a few mA; you get 1A only when battery really needs nthem, for fastest safest charging.

While a constant 1A current for 2 or 4 weeks will damage it.

Oh, youīll need a small heatsink for the voltage regulator.

If you donīt want to use a laptop brick,use a 16VAC 1 to 2A transformer, a 2 or 3A diode bridge and a 4700uFx25V electrolytic as a primary raw voltage source.

Thank you, that's a neat little solution If I can find a generic 2nd hand 15v adapter on ebay I could probably make this even simpler and do away with the 7815?

Have you tried plugging the charger in and taking an actual output voltage reading ??

I'm going to get my hands on it later this week to look at it in person and will report back, but I'm not expecting it to be more than 12v. The power supply is tied directly to the battery and the circuit, there is nothing regulating the battery in any way so if the power supply is putting out 12v, that's all the battery gets.

Any ideas why there is so much noise coming from *any* power supply used on it? I can't imagine they were like that from the factory!

[J M Fahey]

Thank you, that's a neat little solution If I can find a generic 2nd hand 15v adapter on ebay I could probably make this even simpler and do away with the 7815?

NO.

Your generic adapter will supply 15V, period, so it will *explode* trying to feed many Amperes a discharged battery, and straight 15V will overcharge and dry your battery.

Read the principle of operation I fully described.

My charger will offer a *sliding* voltage from 10 to 14.4V which your generic charger will NOT

Mine is 1A current limited which yours is NOT

Mine will stop at 14.4V which is safe and by then provide just a few mA trickle charge which yours will not.

* donīt be mistaken by the apparent simplicity , thereīs way more than meets the eye.

[jondoe]

NO.

Your generic adapter will supply 15V, period, so it will *explode* trying to feed many Amperes a discharged battery, and straight 15V will overcharge and dry your battery.

Read the principle of operation I fully described.

My charger will offer a *sliding* voltage from 10 to 14.4V which your generic charger will NOT

Mine is 1A current limited which yours is NOT

Mine will stop at 14.4V which is safe and by then provide just a few mA trickle charge which yours will not.

* donīt be mistaken by the apparent simplicity , thereīs way more than meets the eye.

OK , does your circuit vary the voltage over the charge period? Is the current draw dictated by the charge level of the battery? I'm trying to make sense of it and doing a bad job
I've noticed the factory batteries are AGM, so it would probably require a charge voltage more around the 15v mark.

The original charger is 15v 1A, so would have fed into the battery directly, I wonder why theirs doesn't explode? Perhaps a similar circuit in the adapter? It also seems mine is an older model, the newer Hog's have an amber low battery warning light, no such delights on this one!

[J M Fahey]

OK , does your circuit vary the voltage over the charge period?

Yes.
In a nutshell:

* it *tries* to supply 15V regulated , minus 1 diode drop of about 700mV so tops is 14.4V ... which happily is a car industry voltage standard, so without extensive tests I know is safe.

* it *tries* to supply as much current as a discharged battery can take, which can be MANY amperes, but all 78xx regulators are internally limited by their own short protection to 1A , so thatīs all that will come out, no matter what.

But it will not fully shut off, it will keep supplying 1A so voltage will slide up/down whateverīs necessary to keep 1A through, so it will tightly track battery voltage to do that.

Who would have thought? ... a tight voltage regulator sliding voltage up and down to accomodate load?

Truth is I had already designed and used for years a discrete regulator doing exactly that, and one day while sipping some coffee it clicked that LM7815 had some of those features built in , for its own use, so .....
And being a mimimalist at heart, after some proof-of-concept experiments found it worked very well.

Is the current draw dictated by the charge level of the battery?

Battery charge current is always 1A until it approaches 14.4V so it charges "as fast as possible" and then reduces to a few mA trickle charge.
And in no case it will go above 14.4V .

I've noticed the factory batteries are AGM, so it would probably require a charge voltage more around the 15v mark.

The notebook brick already provides 19V (typically) , enough for the 7815 to do its magic trick; my own supply (notebook bricks are expensive here, and used ones are sold almost same price as new) uses a 15VAC 1A transformer plus bridge and cap for some 20V DC .

A 15VDC supply is too low to allow a regulator to work , which needs some 3V in-out difference.

I *guess* your Pignose 15V supply , at least the cheap version, is simply a standard 15V supply, regulated or not , might be as crude as a nominal 12VAC transformer, a bridge and a capacitor, which puts out some 16VDC under light load, and a series resistor to limit current.

Such supply needs:

* enough series resistance so charge current is not above 1A even with a fully discharged battery, so15V-11V)/1A=4 ohm 4W . Of course, use 5 to 7W.

It will supply 1A at the beginning, same as mine, so you will have a good initial charge.

But after a few minutes, voltage rises to some 12.5V or so, and current drops to (15V-2.5V)/4 ohm=0.625A so charge will take 60% more time, say 16 hours instead of 10.

Since charger is typically unplugged next morning (to go busking away) , battery is chronically undercharged.

It wonīt last as many hours playing time and to boot is almost guaranteed to be deeply discharged (you have people around and want to keep playing to keep tips flowing or simply for fun).

* when battery reaches 14.4V it will still be receiving 0.7/4=175 mA while the controlled circuit will drop that to "a few" mA.

That said, the simple 15V+4 ohm charger is not that bad, itīs usable, just takes longer and requires some attention so as to unplug it , so itīs the most popular one.

But for a couple bucks extra, a much better one can be built.

The original charger is 15v 1A, so would have fed into the battery directly, I wonder why theirs doesn't explode? Perhaps a similar circuit in the adapter?

See above what I think it has.

Definitely some kind of current limiter, at least a resistor, although it "might" use a lossy transformer so you "see nothing special" if you open it.

Personally I prefer something cheap and external (a resistor) to dissipate those initial 4W of heat instead of the transformer itself but a penny pincher might think otherwise.
And the transformer is cheaper

You can add the Low Battery indicator, just an 8.6V Zener (is there such a value?) in series with a 100 ohm resistor and a Red Led , you may add a series n.o. pushbutton labelled "test battery".

Led will shine *bright* (39mA) when battery is being charged to 14.4V ; quite visible when in use (12.6V so 21mA through Led) and zero-zilch-nothing when battery reaches exhaustion level 10.5V ... and very weak anyway before reaching that, so when in doubt you just push the test button and if no Led visible itīs time to pack home.

In any case battery will soon fully die on you, so ....

Once you think all small details itīs actually quite simple.

EDIT: remember that in no case a fixed voltage supply is suitable to charge a very low impedance variable voltage battery.
You always need higher than maximum voltage and some kind of current limiting.

[jondoe]

Thank you for the explanation

[Mick Bailey]

I built a charger for one of these amps earlier on this year. I used a pair of LM317 regulators - to regulate both current and voltage so that the batteries are charged at 10% of their rated capacity. The original charger supplied always under-charged, leading to shortened lifespan. The new charger works really well with a 19V laptop supply. I built it into the amp and labelled the chassis with the new voltage requirement.

[J M Fahey]

The original charger supplied always under-charged, leading to shortened lifespan.

Yes, thatīs what I foun d with the generic cheap chargers.
Even if "factory labelled and supplied"

I sold tons of "Callejero" ("Street Guy") amplifiers and keep in touch with users; they tell me that they never ever get "unpowered", even with full day busking; the point being that even with "8 hours" use they actually play 4 or 5 hours; you have to stop now and then between songs, say some jokes or stories, even "finish" a show for a few minutes so onlookers go away and new ones arrive later, etc.

Plus they sing and play instruments, not a continuous full power sinewave.

In fact, now and then somebody complains:
- "I got out of juice 3 hours into the show"
- "DID you recharge last night?"
- "ooopsss , I didnīt since it was still charged"

[jondoe]

*drum roll*

So I got my hands on the Pignose supplied adapter and it is labelled with DC12v 2000mA output, but, it's not. It outputs 14.92v with no load, with a battery connected to the amp this dropped to approx 13.5v while charging. It's also called a battery charger, not a power adapter, so I think the mystery is solved, it is actually a charger after all.

I've looked up the charger and they seem to be a cheap Chinese OEM brand, probably $4 worth on aliexpress, nothing fancy My friend ended up paying about $59.... eek!

[J M Fahey]

Please measure current itīs supplying when output drops to 13.5V . (hint: I want to calculate internal resistance).

And if you ever open it, now or in the future, please post some gutshots.