Can a 12VDC 500ma wall wart trickle charge a car battery?

Can a 12VDC 500ma wall wart trickle charge a car battery or must the voltage to charge a car battery be greater than 12VDC (like 14 or 15 volts?).

Can a well regulated 12VDC still charge (over a long time) a car battery?

Or must it be over 13.5 volts to (eventually) accomplish full charging?

Reply to
John
Loading thread data ...

Unless they are regulated many of the 12 volt wall warts put out over 12 volts. It may not charge a car battery very much if it is one of the unregulated ones ,but will maintain the charge.

A well regulated 12 volt supply will not charge a car battery as it 12.6 volts when charged.

It will take a higher voltage than 13 volts to charge a car battery.

Unless precautions are taken just hooking a power supply to a car battery could damage the power supply especially if it is a regulated one.

Reply to
Ralph Mowery

John wrote: =================

** Yes.

**No.

** Yes.

........ Phil

Reply to
Phil Allison

Ralph Mowery wrote: ================= >

** Un-regulated ( transformer) AC to DC adaptors were banned in many places a few year ago.

The only kind allowed now are SMPS with self shut down when unloaded.

( AC to AC adaptors and special multi- voltage ones are excepted )

..... Phil

Reply to
Phil Allison

It will depend on: is it an antique wall wart from the junk box (with an iron core transformer, a rectifier and an electrolytic) or a modern switchmode wall wart?

The latter will do absolutely nothing. The former may work, depending on the parameters.

Reply to
Rob

Lots of things wrong here:

  1. Common flooded car batteries will not charge using a small trickle charge. You can use a trickle charge to maintain the charge level of an already charged battery, but you cannot take (for example) a half charged battery and bring it to full charge with a trickle charger.
  2. The charge voltage on a common flooded car battery is about 14.5V and varies with temperature, battery condition, battery age, etc.
  3. A linear 12VDC/500ma might have a no-load output voltage of perhaps 15V, but under full 500ma load, will probably drop below 12V making battery charging problematic. A switching type power supply has a built in voltage regulator and will produce 12.0V at any load below 500ma making battery charging impossible.
  4. A power supply that produces 13.5V will not charge a battery with a no load voltage of 13.6V (fully charged). You need a voltage difference to produce charging current.
  5. Today's overpriced car batteries cost about 0. Would you really risk trashing a 0 battery because you don't want to use a proper battery charger? I wouldn't. Unfortunately, a charger with a fancy label is not a guarantee of quality. All these chargers were defective in some manner. They also killed two rather expensive stationary batteries at a radio site: Spend some time and do some reading on chargers.
  6. If you're looking for a "battery maintainer", I suggest you check what is being offered for boating. They tend to be better built, be better designed, and unfortunately cost most, than the common automotive and home user variety. RV and recreational maintainers are in between. If you don't like the prices, remind yourself what a new battery might cost if your charger tries to kill it.

Good luck.

--
Jeff Liebermann                 jeffl@cruzio.com 
PO Box 272      http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

Yes, even high dollar charges do not guarenee they will not fry a battery.

At work we had some stand by pumps for fire protection. The batteries to start the Diesel engines were under constant charge by some very high dollar chargers. We would only get about 3 months of service out of the batteries. The engines (we had 2) were started for about an hour every week as a test. I don't think they were ever used because of a fire.

We even had a battery charger company service man to come by about 3 or

4 times because the chargers were cooking the batteries. The batteries were the old lead acid type and were checked for water and specific gravity every week.

If not for the voltage of them, we probably would have been better off with the $ 10 Harbor Freight Battery maintainer.

I bought one of those to put on my 3.5 kw portable generator and hook it up for a day or so every month. The battery is no where near the size of a car battery.

Been working ok for the last 2 years.

For my lawn tractor that is not used from about November to March I have one of the solar cell battery maintainers as there is no power in the shed for it. Seems to keep the battery charged.

Reply to
Ralph Mowery

Theoretically they are not banned, but to be allowed, they would have to have very low standby consumption which might make them uneconomical to manufacture.

I have seen a few sold recently in Australia, but have not investigated whether they really have very low standby consumption or are just non-compliant.

Reply to
Chris Jones

Why is that Jeff? Surely any charger that exceeds the self-discharge current will eventually charge the battery?

Reply to
Clifford Heath

Chris Jones wrote: ================

** Yep - I know all about the MEPS regulations. My colleague Rod Elliott attended one of the " stake holder" meetings in Sydney.

As with the case of incandescent light bulbs, the rule was made ( exquisitely) to exclude them and transformer external adapters. Initially it affected all such, including AC- AC types - but was amended under protest that there was NO alternative.

Now, it is possible to make a low standby, AC -DC adapter with an iron transformer.

  1. Double the usual primary turns to lower I mag.
  2. Use a toroidal core.

The first will mean the VA rating is halved and regulation is poor. Using larger core does not help - cot is involves doubling Imag.

The second is out of the question since it is not possible to make a regular toroidal that complies with the safety standards. External adapters are "prescribed items " that must pass lab testing for user safety under all overload, spike voltage and overheating scenarios. The extremely close proximity of primary and secondary windings does not permit this.

The JOKE is that SMPS adapters are inherently unsafe - though technically complying with the existing rules. Liquid ingress, the failure ( leaking) of an electro cap or the often fake Y-cap fails and bridges isolation.

MEPS enthusiasts were not interested in facts, user safety was not their problem.

Cos they were saving the planet.....

..... Phil

Reply to
Phil Allison

Usually such regulations cover the use of an adapter as part of a system, e.g. a phone charger or a newly designed device with 12V power wall wart, but it does not preclude the sale of the separate component e.g. to use it as a service part for older equipment, or the sale of old stock.

So it is likely still legal to sell old style wall warts which could be used in this application, you just won't find them packaged with your new toys anymore.

Reply to
Rob

I don't know and I've never seen it explained in print. Someone told me that many years ago and my experience seems to verify the claim. When I've tried to charge large lead-acid car batteries which have been substantially drained (about 50%), with a small "battery maintainer" or "battery tender", it has usually failed to charge. Not always, just usually. With small lead-acid batteries, it will charge. Unfortunately, I haven't made any proper measurements. Just the usual RV, boat, radio site, home backup, generator starter, type operation. There are a few clues here and there. For example: Charging Capability All three battery tenders can charge smaller vehicle batteries such as motorcycle and ATV batteries. However, only the 4A and 5A battery tenders can charge car and SUV systems, due to their higher power output; the 1.25A battery tender can only maintain car and SUV battery systems. (...) Unfortunately, the Battery Tender 1.25A cannot charge anything larger than an ATV battery. You can use it to maintain the car battery, but do not expect it to charge it.

Fasten your seat belt before checking the price of a decent battery maintainer: I had something similar on my emergency generator. Note the larger yard tractor battery instead of the tiny stock generator starting battery. The generator had a built in charger module that blew up. So, I keep the battery charged with a battery maintainer (not shown). I'll run the battery down to about 60% and see what happens (if I can find where I put the battery maintainer).

It is not beneath my dignity to plug a large battery charger into the generator, and use it to charge the generator starting battery. I'll eventually be converting the generator starting battery to LiFePO4 plus supercaps. One advantage is that the battery has a very low self-discharge rate. Instead of a battery maintainer, I only need to fully charge the battery and disconnect the charger. The charge holds at about 80-85% for many months.

--
Jeff Liebermann                 jeffl@cruzio.com 
PO Box 272      http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

No, one of the ones I purchased fairly recently was packaged with an appliance sold at a physical shop in Australia and has seemingly genuine Australian compliance markings on it - it is not some banggood grey import. I still suspect it does not meet MEPS rules (as it was not an application where it would make commercial sense to make a special efficient transformer instead of using a SMPS) but so far I haven't bothered to test it.

Reply to
Chris Jones

It could be something as simple as self-discharge being much larger when a battery has been "substantially drained"...?

Yes, I use LiFePO4 also. Self-discharge is 1-2% per annum, and the columetric efficiency is very high also (you get back almost all the charge you put in). Great batteries.

Reply to
Clifford Heath

Ok I am not familiar with the situation in Australia, but here in Europe most equipment is delivered with SMPS wall warts these days, they probably are cheaper as well. And I have done some testing with a power meter (HOPI) and most of them consume no measurable power when unloaded. That was the objective of the regulation, so it achieved that goal well.

Reply to
Rob

Yes here also, nearly every wall wart is a SMPS, partly due to regulations in the EU (they likely come from the same factory just with different shaped pins on them), but partly because of similar local laws that require low standby consumption. That's why I was surprised to receive one of the heavier sort with a new appliance.

Reply to
Chris Jones

Much as I like to speculate about things I'm not quite sure, I'll take a chance and add a few guesses:

  1. Extremely crude battery maintainers are common. Just fixed maximum voltage source and a series resistor. As the battery voltage approaches the voltage source voltage, charging slows down and eventually stop. Pick the wrong voltage or series resistor and it might never get to full charge. Variations in line voltage can also create problems with unregulated battery maintainers.
  2. Flooded cell batteries are quite sensitive to temperature. The better chargers have circuitry to compensate for temperature effects. The really good one's have an external thermistor sensor that attaches to the battery. The best have individual voltage and temperature sensors for each cell. Crude temperature compensation assumes that the battery and charger are at the same temperature. That's often not the case, such as the battery sitting on a cold concrete floor, while the charger is in a relay rack full of very hot radios. I've seen this all too often at radio sites.
  3. Self-discharge in flooded cells batteries increases with temperature. See Fig 6:
  4. Flooded batteries that have lost water and have exposed the tops of the plates to air act weird. One effect is an increase in self discharge rate, possibly caused by internal self-heating from self-discharge. For example, losing 50% capacity from a flooded lead-acid battery in 6 months would be half of the manufacturers rated capacity of perhaps 70 amp-hrs or 840 watt-hrs.
420 watt-hrs / 180 days / 24 hrs/day = 0.1 watt/day That doesn't seem like much, but that's under fairly ideal conditions, with a new battery, no sulfation, etc. The self-heating will be slight, but if it causes additional self-discharge, the effect is positive feedback and might result in enough self-discharge to interfering with low level charging.

Yep, they're amazing with the added bonus of having a 3.3V nominal voltage which produces almost the same voltage as a common automobile battery (4S = 13.2V). They're also good for a much larger number of charge cycles than ordinary LiIon cells. LiFePO4 = 2000 cycles LiCoO2 = 400 cycles Lots of other advantages (such as not catching fire or bulging), but there are also problems. Plagiarized from:

- Keep the battery temperature under 45 Centigrade (under 30C if possible) - This is by far the most important!!

- Keep charge and discharge currents under 0.5C (0.2C preferred)

- Keep battery temperature above 0 Centigrade when discharging if possible - This, and everything below, is nowhere near as important as the first two.

- Do not cycle below 10% - 15% SOC unless you really need to.

- Do not float the battery at 100% SOC if possible.

- Do not charge to 100% SOC if you do not need it.

My plan for an emergency generator starting battery is quite different. I plan to use a fairly small battery pack. It can be almost anything. Initially, I'll start with a 12V 7AH AGM battery. Across the battery are 6 super caps: $21 I'm not sure of the size needed yet. The super caps provide the high motor start current needed. The AGM battery keeps the caps charged. A small float charger keeps the AGM battery charged between starts.

--
Jeff Liebermann                 jeffl@cruzio.com 
PO Box 272      http://www.LearnByDestroying.com 
 Click to see the full signature
Reply to
Jeff Liebermann

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.