Car battery charging current.

[Paul]

Maybe the output of the Aldi is defective ?

Do you have any other batteries you can test it on ?

If the Halford one can show it up like that, it sounds like more than just the battery at fault.

*******

When measuring current with the multimeter, you have to plug the leads into different holes. There is a specific hole for current, to one side of the volts hole. Even if the meter is not powered, the shunt from "Current In" to "Common" will still be present and conducting.

--------X 20A COM X-------------- <=== in series with battery, | | NOT across battery! +---x- 0.01 ohm -x---+ Resistor stays ^ ^ in circuit, even | | if meter knob is +-- meter ---+ rotated. measures drop here

You can see in this sample schematic (for my meter), that the 0.01 ohm shunt is not switched out by the rotary knob.

If the multimeter fuse is blown, the "0.01 ohm" path will be an open circuit.

Aldi ---- red --------X 20A COM X--------- Battery -------+ | | (+) (-) | +- 0.01ohm -+ | | Aldi --- black ---------------------------------------------+

You would also have to make sure the electrical connections are reliable, as some circuits, if the path was interrupted for only a short time, they would notice that.

Also, if you have *two* multimeters, you can use one multimeter on "ohms", to verify the current flow path from 20A to COM is "always on". Or, if you've blown the fuse, the second meter can tell you if the path is "always open" due to the fuse going on it.

I've known a few people to have blown the fuse on the ammeter part. Since I never ever use the ammeter holes on mine, they're mint :-) I use the clamp-on DC ammeter for safety reasons. The clamp-on has no duty cycle limit, for one thing. The clamp-on meter uses the magnetic field around the wire, as a proxy.

Two meters make great pals. Especially when they read consistently (agree on stuff).

Paul

[AnthonyL]

[Dave Plowman (News)]

Sounds like it is sensing the battery is full?

Never been a lover of battery volts telling you much off load. A freshly charged battery will show a much higher voltage than it will a day later. But it won't actually have discharged at all in that period with no load.

2.2v used to be the schoolboy figure for a full charge per cell which would give 13.2v. But something like 12.5 is more realistic as things settle.

[AnthonyL]

[bert]

In article [e-mail]>, "Dave Plowman (News)" [e-mail]> writes

OK experts.

My leisure battery on the caravan has gone flat, so flat that my (very old) Halfords Automatic charger won't start charging it. What would be the result of linking this battery across my car battery in terms of how quickly it would charge and would it damage the leisure battery?

[Dave Plowman (News)]

Many modern chargers need some volts from the battery to connect to it. If you link another battery to it and the charger at the same time, that will let the charger connect. Then disconnect the spare battery. The charger should then carry on charging the flat one.

[Vir Campestris]

Why don't you connect them via a spare headlamp bulb? That should draw about 5A at first, dropping off as the leisure battery gets off the floor.

Conveniently the bulb resistance will drop as the volage difference reduces :)

Andy

[Paul]

The purpose of the bulb, is to reduce the current flow when one of the batteries is really flat. If the bulb was a turn signal, the initial current flow is 1A or 2A or so. If the bulb was a headlight, the current might be 20A. Either would do, from a "reducing current" perspective. If you used "just cables" and no bulb,

100A could flow for the first bit of time, which might make everybody but you happy. The battery on the left has "CCA" cranking-amps, so it can easily push 100A, but the sparks thrown aren't all that nice. What you don't want, is for any hydrogen gas to be ignited by sparking. A turn signal bulb does not eliminate sparking, but keeps the sparking down a bit. The light from the light bulb will handily dim, as the flat battery ends up with some standing voltage on it. As the battery on the right fills, the bulb goes out (stops lighting). +------- 12V_bulb -------+ | | | +------+ | +-------+ | | | | | | (+) (-) | (+) (-) | | | | | | | | 12V Battery | | | 12V Battery | | | | | | FLAT | | +--------------+ | +--------------+ | | | +-------------------------+

The knee of most batteries is pretty sharp, and it should not take long before the 12V FLAT battery is raised to say, 6V. And then, the polarity detection on the "smart charger" will be able to tell a battery is connected, and it's connected correctly to continue charging.

I don't think the manual for my smart charger, says what the minimum is, for it to start working.

To hook up a light bulb, you might need to have a socket to hold the bulb. This style of item gives you the two wires, and you'd have to strip the insulation and use some alligator clip leads to finish the wiring job. I never seem to have enough of those (home-made) alligator clip wires around.

You can solder wires to light bulbs too, but only if they're suited to this. Some styles, the wires don't take solder all that well.

You *could* do it with cables, if you like to see sparks fly. Also, depending on what loads are already on the left-most battery, you could set off the tamper on the alarm system if one is present. With the light-bulb limiter, there are fewer theatrics.

Paul

[williamwright]

No I'm making a fool of you; which is an easy task.

Bill

[williamwright]

Nah! There's no need nowadays.

Bill

[The Natural Philosopher]

I used to respect your knowledge, Bill. Its sad

[williamwright]

I never respected yours, because so often you were proved wrong.

Bill

[bert]

In article [e-mail]>, "Dave Plowman (News)" [e-mail]> writes

Always struck me as a bit odd to produce a battery charger that wouldn't charge a flat battery, but that's progress.

I connected the LB across the car battery and left engine running just for a few minutes, Then disconnect and reconnected battery charger. After just a few minutes it went from charging to charged so disconnected. Left battery for a few hours then checked voltage to find it was below

12 and slowly falling. Left it overnight when it was down to about 10. Put it back on charger and hours later it was saying charged. Left it again and now it is sitting at 12+ and stable. So was it initially fully charged by the car alternator or was something initially confusing the battery charger? Maybe I didn't leave it long enough before reconnecting the charger and it was till showing over 12v although nowhere near charged? The good news is I appear to still have a fully functioning battery!

[Dave Plowman (News)]

It is the easy way to protect the charger from reverse polarity connection. You have a relay on the input fed from the battery via a diode. It will then only make with correct connection.

Older chargers would simply blow a fuse, if reverse connected. Know which I prefer. ;-)

[tabbypurr]

Sounds a bit OTT. I'd just connect the batteries. Different story if you need to do it on a regular basis, but if you do the setup needs sorting, as lead acids hate going flat.

You're not going to get hydrogen by charging from another 12v battery, it requires more volts to split the water.

NT

[mm0fmf]

Nice burn.

[Paul]

Load test... then recharge.

If you had a 12V @ 100Ah battery, that's 1200 Wh. A 60W bulb would last 20 hours. Put a light bulb or two on the inverter as a test, and run it for a bit. Like say, for 1 hour. If the battery flattens in 1 hour, and is below 11.8V or so, you have your answer (knackered). A good inverter, stops driving the load, when the cell voltage drops below

11.8V or so. Your "flat" result, is perhaps a self-discharge, which the inverter could not do anything about.

If it doesn't seem that full based on the load test, the smart charger might not be working right. Which is always a possibility with modern electronics. But bad batteries are so common, if you were betting on the problem, you'd bet on the battery being bad.

Using a dumb charger, and watching a battery shoot up to 15-16V after 5 minutes, that's usually a giveaway that the battery is sulphated or something. A good battery tends to "squash" those voltages and when the relatively-low-current dumb charger is connected, the voltages stay down better while it fills. When topping up a battery, my 6 amp dumb charger would use maybe 1 amp or so when the battery voltage is "flying high". That means the battery has achieved a high flying result, with little in the way of current flow coming in.

Paul

[The Natural Philosopher]

not really.

so into the kf with both of you.

[michael adams]

To the untrained eye, this looks like a casting and weighs 0.2kg or 7.oz

Whether that weight is impressive or not, I dunno

From memory (very long term) and a quick look at Google images pressed steel pulley wheels came in two or more parts - two dished circular blanks which were riveted or welded together. The above wheel looks to be one piece, to me at least with no obvious joins and no rivets or similar holding the two halves together.

michael adams

...

[michael adams]

Although on second thoughts if it was the other way up maybe the rivets are on the uderside in the photo...

If only Sainsbury opened at 7 like all the others