12V Charger and Power Question !!!

[Jimmy_GT-R]

Right heres the deal I need to know if I can at home connect my 12V(only) R/C battery charger straight to my car battery charger and use this to power the charger instead of charging up a 12V battery and using this. As I am getting fed up at home charging the 12V battery all the time to power the charger.

I use my charger at 4amps and my car charger has output of 12V and 4Amps, so I assume its all compatable and safe. Can anyone confirm this 100%. Need to know ASAP.

Thanks

James

[smallman28]

I tried it when I was younger and it didn't seem to work,would charge battery but never seemed to fully charge it,does that make sense?

[Jimmy_GT-R]

I thought it should though, As the car charger is basially acting as my Radio Control Battery Chargers powr source, so I assumed it should charge ok. Its a Eagle racing pocket quick charger with a delta peak cut off. And my car charger as stated runs an output of 12V at 4amps. Don't want to blow anything up just incase. lol. [8)]

Thanks

James

[smallman28]

I think it is something to do with the fact that a charger is much "slower" than a car battery,a charger gives its output over a much longer period of time than what a car battery is capable of.

Try it and see,won't hurt,its just what I remember from when I was younger,for all I know the car battery charger I was using might have just been duff!

[jozza]

I'd advise don't do it. The output from a charger is not the same as the output from a charged lead battery. The only (possibly) safe way to do it is connect the charger to a battery, and then connect your nicad charger to that. Still not recommended though, it's best to charge a leisure/car battery and use that, or use a proper switched mode power supply designed for the task.

Most modern battery chargers test the output of the battery to see how much current to put out, and therefore won't work properly if connected directly to a nicd charger, and some more sensitive equipment may get fried by the output.

For the price of a power supply (about 30 quid) I'd say it's just not worth the risk.

[Jimmy_GT-R]

Well my problem is that I have a leisure 12v battery to power my R/C charger but when fully charged it can only manage to fully charge 3, 3000Nimh battery packs, which just is not good at all, when practicing and trying our settings. Would a car battery last a little longer and charge the battery packs maybe twice each??

Thanks

James

[GPZ1000RX]

The short answer is, no you can't use your full sze car battery charger to run your nicad charger. At least not unless it's far more sophisticated than most!

If your "leisure" battery is the usual size (60AH+) then it should be capable of charging around 10 3000mAH packs and still have plenty left from one overnight charge. You may have a worn out leisure battery or perhaps the charger you use to charge that is faulty.

Check all the above first, but you can buy a suitable "switch mode power supply" from places like Maplin for around £60 or less.

A 13.8V 10A one would be fine. It can be used to power your Nimh charger and to charge a 12V lead acid too!

I'll see if I can be more specific for you tomorrow.

[WillyChang]

You can't use a car battery charger as a Power Supply Unit as its not designed to provide a filtered & regulated source of 12V DC. When there is high current drain at its output, it cannot maintain the voltage and the voltage drops.

A peak-detect charger needs a regulated & stable 12VDC input otherwise it'll get confused.

Chargers rated at "4 Amps" usually means "peak" too... actual current produced is "RMS" and is lower than 'peak'. Read the fineprint, not just what the advertising gurus write on the machine.

If the charger cannot keep up with the current being drawn, the voltage drops even quicker.

What you CAN do is... use the charger to charge your 12V battery. At the same time, run your 7.2V charger off that battery too.

The battery acts as a current/voltage buffer and maintains the clean 12V DC supply. The charger keeps it topped up & you'll be able to do more than just 3 packs.

quote:

Originally posted by GPZ1000RX

A 13.8V 10A one would be fine. It can be used to power your Nimh charger and to

charge a 12V lead acid

too!

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id="quote">id="quote">

NO!

Do NOT use a powersupply unit to charge a 12V lead acid.

The PSU will keep pumping the current in even when the lead acid is fully charged... you'll bubble off all your electrolyte (acid) and create a very dangerous situation.

Proper lead acid chargers are designed to turn the current down as the lead acid battery's voltage rises to the 'full' level.

[Jimmy_GT-R]

Right so after all this info just to clarify. I CAN run my "charger" from my battery and at the same time, have the "car charger" charging the 12V battery to keep it nice and topped up?? But wouldn't the 2 chargers cables touching basically mean that the car charger is running my peak charger. Or I take it thats what you meant when you say the battery is a buffer for making sure a nice and constant current of 12V DC gets to the peak charger. Hope this made sense as I am all a bit confused and new to this 12v charger deal. I used to run mains ones only. But there too slow now for my needs.

Thanks for all the help guys,

James

[WillyChang]

quote:

Originally posted by Jimmy_GT-R

Right so after all this info just to clarify. I CAN run my "charger" from my battery and at the same time, have the "car charger" charging the 12V battery to keep it nice and topped up?? But wouldn't the 2 chargers cables touching basically mean that the car charger is running my peak charger. Or I take it thats what you meant when you say the battery is a buffer for making sure a nice and constant current of 12V DC gets to the peak charger.

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id="quote">id="quote">

yep, spot on.

If your charger pumps out more than 12V, the battery absorbs it.

If the other charger sucks more than "4A", the battery covers that gap and voltage doesn't drop.

When you've finished charging, the full "4A" goes to top up the battery whilst you are not charging.

(And if someone trips over your extension cord & yanks the plug out of the wall, your 7.2V will still keep charging.)

[ideal2k]

You need a proper 12v powersupply. I've got a 10A Mascot unit, works great.

[WillyChang]

In an ideal world that would be best, yes.

But if that's all one is limited to, its an acceptable workable situation.

I use a Novak Millenium Pro which works perfectly off a 12V car battery with a car battery charger hanging off it.

[DJTheo]

quote:

What you CAN do is... use the charger to charge your 12V battery. At the same time, run your 7.2V charger off that battery too.

The battery acts as a current/voltage buffer and maintains the clean 12V DC supply. The charger keeps it topped up & you'll be able to do more than just 3 packs.

---

id="quote">id="quote">

I wouldn't recommend charging or using the car battery while charging a RC battery with it, as during use or charge there may be little voltage peaks or drops which can cause a premature charge shut down because of the delta peak detection of the RC charger.

This can even occur if you open your cars door while charging, because of the interior lights.

Cheers

[GPZ1000RX]

Sorry to disaggree with you Willy but you most definately can use a regulated power supply to charge a 12V lead acid, thats exactly what keeps the batteries charged in nearly every fire and intruder alarm system in the world.

Most regulated 12V supplies are in fact set to 13.8V because this is the correct "trickle charge" voltage for a 12V lead acid (battery charge spec for "dryfit" batteries is actually 2.3V/cell, max ripple 30mV/cell)

If a psu that meets this spec is connected to a 12V lead acid then the battery itself regulates the charge current, which falls away to virtually nothing when the battery is fully charged. It will NOT "boil away the electrolite"

In fact, a regulated 13.8V psu makes a much better charger than the standard auto shop offerings because of this ability to allow the battery to regulate it's own charge rate.

You can pretty much leave a 12V lead acid permanently connected to a 13.8 psu, just like in thousands of alarm installations!

Jimmy, on the original subject, Maplin do the necessary for £35, page512 part no RP08J max current 6A, or, for much more grunt RP09K max15A £80

[WillyChang]

Do what you will but personally have lost count how many gelcells I've replaced in alarm boxes etc over the years. The ones that get "maintained" at 13.5V or higher by their wall-warts are the worst culprits... on a still night one can hear the electrolyte bubbling.

My current PSU is rated at 11A peak @ 13.8V and I've tried loading it with up to 15A (3 chargers) before the voltage started rippling.

Won't catch me using that PSU to charge leadacids... [:0]

[Jimmy_GT-R]

Well I have tried Willy's way, of hooking the 3 up all together to charge the battery and it seems to work. Battery packs nice and full and the battery can last a bit longer with the charger attached to it. Although this seems to be a rather interesting subject, as some people say not to do this and that and others are saying to do the opposite.

Thanks

James

[WillyChang]

That's what we did for TCS 2003. Had a 80Ah leadacid battery with a 5A battery charger on it.

We had 3 chargers running off that all at once, doing enough batteries to campaign 2 cars in Mini class, 1 in Stock and 1 in GT1.

On more than one occasion silly ppl kept tripping over the powerleads and yanking the plugs out. The fellas running PSUs had their charging disrupted, but the leadacid kept things flowing fine for us (until someone discovered the blackout & reconnected the 12V charger).

quote:

Originally posted by DJTheo[/iI wouldn't recommend charging or using the car battery while charging a RC battery with it, as during use or charge there may be little voltage peaks or drops which can cause a premature charge shut down because of the delta peak detection of the RC charger. This can even occur if you open your cars door while charging, because of the interior lights.

id="quote">id="quote">

yep, that's true.

All above is with a 'spare' 12V battery, not the one bolted in the car.

Whenever I use fancy chargers off the auto battery (the one under the bonnet), I turn off all car's interior lights etc so the on/off won't glitch the charger.

(It is probably not a good idea to charge 12V batteries whilst they are connected to your car, it might do damage to the alternator's voltage regulator. Always isolate the battery before charging.)

[GPZ1000RX]

In order to supply some repeatable data for the 12V lead acid battery/ psu debate I'm in the middle of an experiment:-)

I've got,

My 4 year old, 85AH leisure battery, which hasn't been used since last charged about a month ago.

My Maplin 13.8V 10A series regulated psu

My trusty Fluke 77 Digital Multimeter

Checked the psu output off load (13.79V) and battery (12.45V) electrolite OK

Connected the batt and psu together with meter in series and reading Amps

current started at 4.75A

at 60 secs current was below 2A

at 120 secs current below 1A

wthin 15 mins current steady at about 0.3A and batt terminal voltage 13.47V steady.

The conclusion is that there is no way that using this method of charging can do any harm at all to the battery. You can leave it connected like this all year, 0.3A will do nothing untoward to a battery of this size, it may need an electrolite top up every few months but that's all.

Try it for yourself, Willy, I'm sure you must have the psu and meter, if you are worried about the psu output, find the voltage adjust pot and turn it down 1/2 a volt. Let us know your results.

I'm still certain that, if anything, a regulated psu is a better charger for 12V batts than the standard auto shop offerings because the smooth, regulated output allows a fit battery to regulate its own charge current, as demonstrated by my readings above.

The standard "raw" DC from an ordinary car charger prevents this self regulation effect and is much more likely to overcharge the battery (boil it dry) if not carefully timed or the charger "sized" to suit. This is why "car" chargers are likely to destroy "bike" batteries, bike batteries are about 1/4 the capacity of car ones.

Why am I bothering with all this? Well I'm off sick from my 20 year "career" in the alarm industry and I'm starting to get bored!!!

PLUS if another Tamiya kit appears in the near future my wife might just carry out her threat to kick me and my hobbies out!!!!

[jozza]

****, and I just spent £30 on a smart charger for my leisure battery, when I could have just lashed it up to one of my PSU's []

[GPZ1000RX]

I've done that myself, bought an Optimate charger/maintainer for my Kawasaki GPZ1000RX battery a few years ago, it works very well and has a few nice protection, analysis and deep recovery features, but I'm certain that 99+% of the time its just sat there being a nice smooth, regulated 13.8V 0.5A PSU :-)

Cost me £40 and I still had to buy a new bike battery last week.

Life's a beach, so drive a crawler on the dunes!!!

[WillyChang]

quote:

Originally posted by GPZ1000RX

"wthin 15 mins current steady at about 0.3A and batt terminal voltage 13.47V steady."

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id="quote">id="quote">

If you're pumping 300mA in for extended times and the battery voltage doesn't rise beyond 13.5V... it does suggest that energy is all going towards electrolysis of the water. [|)]

Best to read this, great stuff:

http://www.batteryuniversity.com/partone-13.htm

http://www.batteryuniversity.com/parttwo-35.htm

[GPZ1000RX]

Strange you should mention that Willy, I've just done another check after a night on charge.

Current 0.2A Batt voltage 13.73V Psu output voltage (off load) 13.80V

Under these conditions it will use some electrolite if left for months, all "open" lead acid batts need top ups and all batteries have a limited sevice life.

It being a "high cyclic" leisure battery, it's not necessary to leave it on charge. It gets discharged at the track, it gives my psu some serious excersise recharging it for a few hrs and then about a day of gentle trickle charging. Followed by an overnight top up the night before the next meeting.

I've never had to top up this battery or it's predeccesor and that one lasted 6 years before wearing out, both have always been charged with the same psu.

I'll have a look at your suggested sites and let you now what I think. (no surprise there then:-) )

[GPZ1000RX]

I'm still reading Willy, it's all good stuff, I've even added it to my favourites list!

Are we really only arguing over a few hundreths of a volt?

[WillyChang]

haha, ya no arguing here. []

That Battery Uni is interesting stuff, especially that bit about overvoltage and you corrode the +ve plate vs undervoltage and the -ve sulphates.

I've been trying this battery water laced with cadmium that's meant to reduce sulphating and it looks like its doing the job. But perhaps the charger I use is over-volting too... ends at about 14.1V if I leave it on for a few days - corroding the +ve?? [8)]

Have even bought a solarpanel that float charges 100mA into a battery but have yet to try it out.

One point with PSUs, mine is 'fixed' at 13.8V with the rationale its designed for running 12V car gear eg CB radios thus its reproducing the voltage of a proper operating alternator and/or a fully charged battery.

I like 'em fixed voltage as its too easy to accidently shift a knob when carting to track etc then blow up a nice RC charger from overvoltage.

[WillyChang]

ooooh, Battery Uni also tells us the voltage depends on its temperature. Hotter = lower voltage. Interesting!