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Bruce
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12-09-2020, 05:41 AM
1

Car Battery Charging at Idle

I was not doing much today so I filmed how my car, with an alternator but not a "smart" one, charges the battery even at idle. The voltmeter is an el cheapo one but accurate enough for this purpose, the battery has been on an external float charge for a couple of days.



Any voltage over about 12.8v will charge a lead acid battery, from memory about 13.3v is a float charge and anything over 13.7v will cause the battery to gas slightly. I think any voltage up to about 14.4v is OK to bulk charge.

as I say those figures are from memory but roughly right.

What I thought was interesting was the voltage drop when the ignition is first turned on and current supplied to the computer, accessories, glow plugs(?) and modules. It soon returns to normal but it must be quite a surge and I wasn't expecting that.
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12-09-2020, 07:59 AM
2

Re: Car Battery Charging at Idle

This is why they use AGM batteries in cars with stop start and a heavier alternator to handle that type of vehicle. With that one should use a battery charger with AGM charging capabilities. such as the "CTEK MXS 5.0" which I have.
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Bruce
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12-09-2020, 08:15 AM
3

Re: Car Battery Charging at Idle

Originally Posted by realspeed ->
This is why they use AGM batteries in cars with stop start and a heavier alternator to handle that type of vehicle. With that one should use a battery charger with AGM charging capabilities. such as the "CTEK MXS 5.0" which I have.
There are advantages to AGM batteries over flooded lead acid but I don't think they have anything to do with stop start, it is more to do with size and charge retention when not used. In fact AGM batteries have to be charged slower than lead acid ones so a bigger alternator is definitely not needed.

Float charge voltage for both AGM and Flooded is the same but the boost charge voltage for AGM is lower. Most charge and maintain chargers do that anyway there is nothing special about your charger other than the price.

As a starter battery I can't see the advantage in them other than being able to use a smaller battery in size and weight
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12-09-2020, 09:05 AM
4

Re: Car Battery Charging at Idle

Hi

Charging at idle is something I do every other day now.
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12-09-2020, 09:41 AM
5

Re: Car Battery Charging at Idle

why then do they recommend and fit AGM batteries in stop/start cars.
Sorry Bruce that is what I was told by the mechanic when they replaced the battery at the main dealers. I asked specifically as to why and that is what I was told
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12-09-2020, 09:46 AM
6

Re: Car Battery Charging at Idle

Originally Posted by realspeed ->
why then do they recommend and fit AGM batteries in stop/start cars.
Sorry Bruce that is what I was told by the mechanic when they replaced the battery at the main dealers. I asked specifically as to why and that is what I was told
They're newer, more expensive and smaller than flooded lead acid. Why wouldn't you recommend them?

To be honest I can't see the relevance to this thread.
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12-09-2020, 10:18 AM
7

Re: Car Battery Charging at Idle

I never said I don't recommend them, I don't know where you got that from, please show me. The relevance is obvious battery voltage drop and charging type
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12-09-2020, 12:46 PM
8

Re: Car Battery Charging at Idle

Originally Posted by realspeed ->
I never said I don't recommend them, I don't know where you got that from, please show me. The relevance is obvious battery voltage drop and charging type
I meant why wouldn't the mechanic you were talking to recommend them? They make more money from selling one.

I am not saying they are a bad battery particularly as I have one as a deep cycle auxiliary battery. However unless you are keen on saving weight I can't see them being worth the extra cost as a starting battery.

In practical terms their only advantage is the weight saving and I guess that they are sealed but that fact is why they have to be treated with kid gloves because of the danger of overcharging them.

The voltage drop and charging would be exactly the same for an AGM battery as a lead acid the only difference is that an AGM is limited to a maximum charge of 14.4volts as opposed to a lead acid 14.7v but I suspect that most regulators are set to the former anyway these days.

Again all totally irrelevant to this thread. Perhaps you'd care to comment on the video?
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Bruce
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12-09-2020, 12:58 PM
9

Re: Car Battery Charging at Idle

Originally Posted by swimfeeders ->
Hi

Charging at idle is something I do every other day now.
Probably doesn't need to be done that often unless the battery is on its last legs. If a car is not used it is also a good idea to run the AC so the seals don't dry out, they reckon once a month is sufficient for that.
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Bruce
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12-09-2020, 11:39 PM
10

Re: Car Battery Charging at Idle

BTW the video was shot with my Panasonic Lumix LX10 camera mounted on my garbage bin. The camera is set to 1080p at 25fps and mounted using a cheap Ebay copy of one of these Manfrotto mounts. As you can see it is quite a steady mount yet can accommodate an infinite number of positions

 
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