Battery power supplies - lead acid cells

[nat8808]

Hi all,

I have picked up about 8 large, high amp/hour, 12V lead acid batteries in recent months and would like to turn as much hifi in to battery powered as I can eventually.. I think they were all deemed as underperforming in their industrial, high-power drain usage (e.g. a couple were from a small "Genie"/cherry picker type thing) but should still be ok for very low power hifi.

Has anyone experimented with such things or know much about good battery power supply designs?

I read on the odd DIY forums of people saying they are not ideal due to low impedance of the batteries themselves and so many prefer to just build good mains supplies as good designs are so readily available.. yet at the same time many report great results in just connecting some gear direct to a 12V battery.

Would a good design use the usual capacitor bank and then good voltage regulation? Can a battery just replace the transformer/rectifier part of a good 12V power supply design or is there more to it than that?

I would like to see if I can modify a good pre-amp to run off battery supply and also CD transport/DAC at a later stage (my turntable already is battery powered..).

How to incorporate the charging circuit I guess would be the next stage to think about..

Any advice would be greatly appreciated!

[Reid Malenfant]

As batterys don't have infinitely low impedance all you need to do is have a decent capacitor accross the thing when powering equipment. Best not to when no equipment is connected as there is some leakage current.

So battery > switch > capacitor + with the ground permanently connected to both cap & equipment.

I think you'd be surprised how quiet something like a T amp would be as there simply won't be any hum what-so-ever assuming the front end is likewise connected.

To prolong battery life use a constant current charger when not in use :)

[Jonboy]

perhaps a leisure battery would be better as they has low amps but a greater or longer discharge time

[nat8808]

perhaps a leisure battery would be better as they has low amps but a greater or longer discharge time

Sounds a bit blue.. what is one?

I guess I could go the whole hog and use battery supplied T-amps too - not tried a T-amp yet.

So what would happen if I were to replace a transformer/rectifier in a pre-amp (that was outputting about 12v) with a battery? Would everything work fine or would I need to optimise anything?

The Dartzeel pre-amp uses batteries doesn't it?

[nat8808]

oh, and how about earthing?

Does connecting earths to the negative terminal actually worsen the earth because of any kind of battery noise or noise travelling through the battery from the positive end? Should earthing still be connected externally somehow?

[Mark Grant]

many report great results in just connecting some gear direct to a 12V battery.



Remember to make sure its safe, fit an in-line fuse at the battery.

http://www.google.co.uk/search?source=ig&hl=en&rlz=1G1GGLQ_ENUK261&=&q=inline+fuse+holder&aq=f&aqi=g7g-v3&aql=&oq=#q=inline+fuse+holder&hl=en&rlz=1G1GGLQ_ENUK261&prmd=ivns&source=univ&tbm=shop&tbo=u&sa=X&ei=6Y3TTYuVOoy8-QbprI2uCg&ved=0CDYQrQQ&fp=e2e851204c5c9af7&biw=1262&bih=924

If there is no fuse and you accidentally short the wiring out the wire will heat up like a heating element within a second and cause burns or set fire to stuff.

[Reid Malenfant]

A leisure battery is simply one that won't mind too much if it's deeply discharged every so often. Normal lead acid batteries can take offence at this & you might end up with a buggered cell.

Batteries are noiseless. If you happened to have a split rail PSU in your equipment then one battery could power the positive rail with it's negative terminal connected to ground, while the other battery would need it's positive terminal to ground & the negative to the negative rail.

Earthing is generally something that is more to do with mains equipment, it's a safety thing that blows the fuse in the live wire if anything live touches the metal chassis. In order to charge the batteries you'd need some kind of mains charger so there may well be some kind of earthing etc to deal with...

This is all totally hypothetical of course ;)

[spendorman]

What is the capacity of the batteries? liquid or gel electrolyte?

[nat8808]

Good point Mark! I wouldn't have thought of that cos it's just a harmless little battery... that could probably deliver 25 Amps or more, explode or burn the house down!

By earthing, I guess I mean signal earthing, star earthing and the like and that is me getting confused - I guess that doesn't really relate to the battery itself except of course that anything plugged into the mains will also have the possibility of an earth connection via the plug..

[nat8808]

Four of them at least are these: Yuasa npl24-12i (http://www.yuasabatteries.co.uk/npl24-12i-111-p.asp) £75 a pop brand new - hoping these used ones are still ok for low power stuff. Still measuring around 12.8V

24Ah capacity and I guess they are gel if they're the two options as they can be used in any orientation according to their specs. With that capacity, I'm sure they could power many a good power amp, not just T-amps, if enough can be connected in series to get the correct voltage - at that point I start to get worried about safety with current draw, heat etc.

Also designed for standby use they say so hopefully will still be ok by the time I actually get to use them!

[Reid Malenfant]

I'd worry about current flow from just one of those :eek: I have no doubt one of them could happily supply well over 1000 Amps for a short period as i have seen a car started with a 6Amp hour Yuasa :cool:

[spendorman]

12.8 V is fully charged, that's good, look like gel batteries, so need a charger that will not overcharge them.

[Mark Grant]

Good point Mark! I wouldn't have thought of that cos it's just a harmless little battery... that could probably deliver 25 Amps or more, explode or burn the house down!


When I was aged about 7 I accidentally shorted out a car battery while holding the wires between finger and thumb, an early lesson on messing with batteries and bulbs etc :eek: The Smell of burnt skin :eek:

A couple of you tube of videos: ( I cant get them to embed for some reason)

http://www.youtube.com/watch?v=-P4iaHPgmg8

-
http://www.youtube.com/watch?v=P11WbduMKhY

-

[spendorman]

I'd worry about current flow from just one of those :eek: I have no doubt one of them could happily supply well over 1000 Amps for a short period as i have seen a car started with a 6Amp hour Yuasa :cool:

Yes, that current is quite possible.

I've been near a lead acid battery explosion, was very nasty.

[Reid Malenfant]

12.8 V is fully charged, that's good, look like gel batteries, so need a charger that will not overcharge them.
They need a constant current charger, not a normal car battery charger. It needs to be regulated voltage wise & the batteries need to be charged at a maximum of 1/10th the amp hour capacity, better off at 1/20th for longevity.

A 12V gel battery needs to be charged at 13.8V for standby use, i'm not 100% sure for continuous charge & discharge, i'll see what i can find but i think it may be a tad higher :scratch:

[spendorman]

When I was aged about 7 I accidentally shorted out a car battery while holding the wires between finger and thumb, an early lesson on messing with batteries and bulbs etc :eek: The Smell of burnt skin :eek:

A couple of you tube of videos: ( I cant get them to embed for some reason)

http://www.youtube.com/watch?v=-P4iaHPgmg8

-
http://www.youtube.com/watch?v=P11WbduMKhY

-

That's nothing to what can happen.

At work I saw a large spanner dropped across the terminals of a large lead acid battery. Almost instantly it glowed red then bright red, someone levered it off with a broom handle. Spanner was completely bent.

The battery exploding was a 300+ AH 36V (half ton in weight). There was virtually nothing left of it. Room was filled with smoke and acid fumes. The batteries were used in electric vehicles.

[nat8808]

I'd best make sure they stay in their boxes and away from spanners of both the metal and human kind...

Maplin do sell constant current chargers but perhaps not for this size - may have to splash out on something from RS.

[Reid Malenfant]

If you can understand this then you are doing better than me :eyebrows:

Cyclic charging regime for NP type gel batteries :scratch:

4551

[spendorman]

If you can understand this then you are doing better than me :eyebrows:

Cyclic charging regime for NP type gel batteries :scratch:

4551

That does look confusing, even after being on a lead acid battery/ charger training course! But that was about 25 years ago.

I have a charger similar to the one below:

http://www.sainsburys.co.uk/sol/shop/home_and_garden/car_care/109006810_ring_powering_smart_battery_charger_24am p_12v.html?hnav=4294966984#infobox

Can safely charge most 12V gel batteries as well as liquid electrolyte ones.

Mine was only about £10 from Lidl

Just found a pic of the Lidl one charging a battery:

http://www.pistonheads.com/gassing/topic.asp?h=0&t=724322&d=10969.08575&nmt=

Have to scroll down a bit to see it

[spendorman]

Reading the spec of the Lidl charger, It says suitable for Gel or wet 12V batteries of 1.2 AH to 120AH. A "three phase-charging strategy" enablers the charging of the battery to almost 100% of it's original capacity. Furthermore, a long term connection of the battery to the charging station can take place to keep the battery in optimal condition when not in use without it being damaged in the process.

There is a choice of currents, 0.8A or 3.6A and reverse polarity connection protection.

[Reid Malenfant]

The thing is the charging voltages are different for standby batteries which require a 13.8V charge & those batteries that are going to be regularly discharged & recharged. When i saw that graph earlier the one line on it that stood out was the one going to 15V which gives 2.5V per cell - that kind of rang a bell :)

The charger needs to be the correct type, still a constant current charger IE regulated voltage wise with a current limit. If the voltage is too low then the battery will lose capacity over time.

The other thing is that if Darren is connecting them in series he'll either need a charger for each battery or a single charger to do the whole lot in series which would no doubt have to be specially made. The other alternative is to look for something on fleabay that could be modified, possibly an SMPS?

[spendorman]

The thing is the charging voltages are different for standby batteries which require a 13.8V charge & those batteries that are going to be regularly discharged & recharged. When i saw that graph earlier the one line on it that stood out was the one going to 15V which gives 2.5V per cell - that kind of rang a bell :)

The charger needs to be the correct type, still a constant current charger IE regulated voltage wise with a current limit. If the voltage is too low then the battery will lose capacity over time.

The other thing is that if Darren is connecting them in series he'll either need a charger for each battery or a single charger to do the whole lot in series which would no doubt have to be specially made. The other alternative is to look for something on fleabay that could be modified, possibly an SMPS?

About 2.4 v a wet lead acid cell starts to gas.

Yes, if he needs more than one 12V battery charging those chargers won't do say two 12V batteries in series.

For 24 V chargers, perhaps look at disabled vehicle battery chargers. Some on ebay.

My Mum's one has two 12 V 15 AH gel batteries in series.

[Reid Malenfant]

Interesting that you mentioned batteries for electric vehicles earlier Alex :) I used to build & test industrial battery chargers for such things as fork lift trucks etc when i worked at Chloride Electronics.

I seem to remember they (Chloride Spegel chargers) charged up to 2.6V per cell where they should have output about 37.5% of full output current. Once they reached that point they then had a set time to shutdown.

Biggest thing i can remember working on was a 200 cell 50Amp charger that was used to power the small electric trains that took workers to & from the boring machine making the channel tunnel ;) I remember one of the rectifier stacks going up like a rather oversized roman candle whilst in the test bay :stalks: :eyebrows:

[spendorman]

Interesting that you mentioned batteries for electric vehicles earlier Alex :) I used to build & test industrial battery chargers for such things as fork lift trucks etc when i worked at Chloride Electronics.

I seem to remember they (Chloride Spegel chargers) charged up to 2.6V per cell where they should have output about 37.5% of full output current. Once they reached that point they then had a set time to shutdown.

Biggest thing i can remember working on was a 200 cell 50Amp charger that was used to power the small electric trains that took workers to & from the boring machine making the channel tunnel ;) I remember one of the rectifier stacks going up like a rather oversized roman candle whilst in the test bay :stalks: :eyebrows:

Blimey, sort of coincidence, I was working on developing electric vehicles, went on courses at Sevcon (I think was the name and made controllers for fork lift trucks) for electronic controllers for DC motors.

Our controllers were transistor output stages as against the usual SCR. Two channels (L and R) 150 A output at 36V per channel.

Yes, our chargers took close to the full 13A from a single phase mains supply.

Yep, Sevcon still going:

http://www.sevcon.com/

[nat8808]

Just as a quick update - I've been powering my Temple Audio Bantam by one of these lead acid cells this week..

Quite a few hours clocked up and still not dropping to below 13V yet and this in their original found state, still don't have a charger!

Still.. I was having a hard time discerning much difference between it and the SMPS it came with. In fact I didn't discern a difference.

[Epiphany Acoustics]

What is the long term safety of batteries like? Say 5 years down the line of constant use, charging etc, are they likely to go bang or anything?

[Reid Malenfant]

What is the long term safety of batteries like? Say 5 years down the line of constant use, charging etc, are they likely to go bang or anything?
No, i have a bunch of lead acid gel battery Yuasas' that are 20 years old. The worst that i have seen happen is one cells plates sulphate up & the whole battery is then useless.

As long as they are charged correctly by a constant current charger they tend to last quite a while. It's constant discharging & charging that ultimately kills them. But assuming they take a good while to discharge, say a week or more on whatever equipment you are powering then they theoretically should be good for 10 years + at 1000 charges :cool:

[Epiphany Acoustics]

No, i have a bunch of lead acid gel battery Yuasas' that are 20 years old. The worst that i have seen happen is one cells plates sulphate up & the whole battery is then useless.

As long as they are charged correctly by a constant current charger they tend to last quite a while. It's constant discharging & charging that ultimately kills them. But assuming they take a good while to discharge, say a week or more on whatever equipment you are powering then they theoretically should be good for 10 years + at 1000 charges :cool:

Interesting. Thanks for your response :)

[Ali Tait]

Just as a quick update - I've been powering my Temple Audio Bantam by one of these lead acid cells this week..

Quite a few hours clocked up and still not dropping to below 13V yet and this in their original found state, still don't have a charger!

Still.. I was having a hard time discerning much difference between it and the SMPS it came with. In fact I didn't discern a difference.

I found a decent linear PS an obvious improvement over the supplied wallwart.

[Paul Hynes]

Beware of connecting batteries to equipment with capacitance on the supply lines. Discharged low impedance capacitors look like a short circuit to the battery for a brief period of time until the charge builds up on the capacitors. The current surge can be surprisingly high under these circumstances and it usually causes arcing across the connection component whether it be a connector or a switch. The arcing will damage the surface of the metal contacts leading to higher impedance connections, poor reliability and eventually failure from contact destruction. It pays to use a soft start circuit to make the connection safely.

Regards
Paul

[aquapiranha]

I arn my Trends TA10 from an SLA and if honest I never heard any benefit. This was using some very sensitive and revealing speakers at the time.

[nat8808]

Beware of connecting batteries to equipment with capacitance on the supply lines. Discharged low impedance capacitors look like a short circuit to the battery for a brief period of time until the charge builds up on the capacitors. The current surge can be surprisingly high under these circumstances and it usually causes arcing across the connection component whether it be a connector or a switch. The arcing will damage the surface of the metal contacts leading to higher impedance connections, poor reliability and eventually failure from contact destruction. It pays to use a soft start circuit to make the connection safely.

Regards
Paul

Interesting point! I've not gone as far as building a proper PS with capacitors etc. I'll have to look into that when I do. I guess that also would apply to powering something with a battery that has low impedance internal capacitors - good idea to check first. Although this probably also applies to any power supply that might be damaged in that way.

[Paul Hynes]

Another thing to be very careful of is to ensure the battery polarity is correct when connecting. It is quite possible to get the polarity wrong, especially when prototyping, if using patch-in leads, which are attached and detached for charging periods. You may be lucky but it usually lets the smoke out of circuit components.

Regards
Paul

[Hypnotoad]

I started using 9v batteries to power my DIY rail to rail op amp phono stages and loved the results. Low noise, no hum and good sound.

Now I have 4 x 6v lantern batteries in series which gives me +12v, 0, -12v for a nice split rail supply. I love these things as they last well over a year and cost so little to buy. You can use XLR connectors or like I did 3 pin Molex and no way to connect them back to front.

Never tried SLA batteries as these are easier.