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Post by charliefarlie on Apr 24, 2020 7:25:02 GMT
That confused me too, as I thought both would REQUIRE to be AGM, as they are linked electricfully, naw Andy.....? All sorts of electrific dark magic going on with these stoppy/starty systems Kev. Stop start is the most stupid daft bloody pointless crap ever fitted to an automobile..... Ever.
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Post by philip42h on Apr 24, 2020 7:56:54 GMT
The wife's V40 XC has a stop-start system. Being a Volvo it obviously has to have two batteries - a big one (the starter battery) that you can see and a not so big one (the support battery) hidden away low down underneath. And the support battery is, of course, an Absorbed Glass Mat (AGM) battery - and you can't / mustn't use a standard charger on an AGM battery. I knew none of this 24 hrs ago! This would be my take on this subject... A vehicle battery with stop/start should not actually be charged fully in the same way as a 'normal' car as the battery needs "room" to take any excess power from regenerative braking. To take account of this, the Alternator fitted to these type of vehicles are 'Smart' Alternators that take account of this requirement. I would think that for this reason you shouldn't keep a charger left on the car long term, just for maybe a couple of hours a week (base the length on any voltage drop). I wonder with the Volvo if it is the 'hidden' AGM Battery that takes this regenerative braking charge? There's no regenerative braking on the Volvo ... it's just a bog-standard diesel with stop start so that it doesn't use fuel while at rest. So, in this case, a 'full' battery (or batteries) is a good thing ... I think ...
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Post by davidwilson on Apr 24, 2020 8:29:11 GMT
Beginning to feel a bit of a fraud with my PhD in physics - I can just about follow Andy's explanations but only just!
I used the CRV for the first time in about 5 weeks on Tuesday to collect essential injections and medications for 3 of our cats. It started perfectly each time so hopefully will continue to do so.
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Post by shcm on Apr 24, 2020 9:30:48 GMT
Beginning to feel a bit of a fraud with my PhD in physics - I can just about follow Andy's explanations but only just! Oh come on! . Probably my crap explanations. Problem is too little info in explaining can be a dangerous thing as can too much.
It's constant current, (voltage will rise up to a set point), then switch to constant voltage (current will gradually drop to a relatively low level), then after a certain time or certain low current level is reached, switch to a slightly lower float voltage.
You can also do "clever" things with various applied pulses.
For spot on pedantry, all the various levels for voltage and current are battery dependant and as David implies, yes, ultimately you have to read the battery data sheet.
We can do CP symmetry violation and neutrinos if you like. .
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Post by Hoovie on Apr 24, 2020 13:50:56 GMT
I do a lot of battery monitoring as it happens, so have some real-life charts of how a charger operates on a battery This one shows nicely the different stages of charging an AGM Battery BT - Ablemail V_C by David, on Flickr From 11:00 to 15:0o, the Voltage is going up, but the Current is constant (and is the maximum this charger can deliver). This mode is known as BULK and also as Constant Current - CC - Mode (for obvious reasons) From 15:00 to just before 17:00, the Voltage is constant and the current is declining. This mode is known as ABSORPTION and also as Constant Voltage - CV - Mode (again for clear reasons) The next Mode is FLOAT, where the voltage drops to a safer level once the charger determines the battery is fully charged to avoid potential damage though overcharging. This charger is set to 14.1V maximum to allow it to work with Wet Cell batteries. For AGM Batteries, I would usually change the voltage to 14.4V in fact. The Charger changes the mode based on how the battery is accepting the charge (batteries are dumb things, just lead and acid and chemical reactions). Generally, the mode changes coincide with the state of charge of the battery (again, determined externally from the battery and also from the charger). This next graph shows the SoC (State of Charge) of the battery for the above charging. BT - Ablemail SOC by David, on Flickr Because the charge voltage is lower than the battery would really like, it didn't end up fully charged before it hit FLOAT mode in this case I have found a charge rate of around 25% (so 25A per 100Ah of Battery) is about right for a decent AGM Battery as a maximum rate. My own battery setup has a 120A Charger that feeds a 645Ah AGM Bank, but rarely goes up to 120A as as the battery State of Charge increase, the batteies accept less and less charge. This is another charrt showing the Voltage and Current rates at the top with this battery bank and charger, and the lower chart shows the mode the charger is in. Remember CC = Bulk and CV = Absorption and you can see how the change in mode equates to the change in the Voltage and Current pattern. 13feb-V&C by David, on Flickr Probably gone off-topic here, but seems to be some interest in battery charging generally
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Post by charliefarlie on Apr 24, 2020 16:49:00 GMT
I’m preparing my technical statement.....
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Post by jasehutch on Apr 24, 2020 18:18:12 GMT
I’m preparing my technical statement..... Will we be able to read it before the lockdown ends ??
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Post by charliefarlie on Apr 25, 2020 7:50:25 GMT
I’m preparing my technical statement..... Will we be able to read it before the lockdown ends ?? Be patient old chap be patient ...........😉
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Post by Deleted on May 4, 2020 21:15:29 GMT
I have just purchased a small 9 stage battery charger just to keep the battery topped up. The handbook says the charger must be plugged into an earthed or grounded mains socket. The plug supplied with the charger doesn't have an earth pin, it only has 2 pins. You have to connect the charger to the positive battery terminal first and then a suitable earth on the car before connecting the charger to the mains. It says it has polarity protection which prevents the output leads from sparking due to accidental reverse connection or short circuit. Well when I connect or disconnect the negative clip from the earth on the car and before I turn on / off the mains input there is always a spark. Is this a fault that I should be concerned about? The man I spoke to at the shop was not sure what to say apart from saying that all their chargers only have 2 pin mains plugs.
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Post by firemac on May 4, 2020 21:20:24 GMT
I have just purchased a small 9 stage battery charger just to keep the battery topped up. The handbook says the charger must be plugged into an earthed or grounded mains socket. The plug supplied with the charger doesn't have an earth pin, it only has 2 pins. You have to connect the charger to the positive battery terminal first and then a suitable earth on the car before connecting the charger to the mains. It says it has polarity protection which prevents the output leads from sparking due to accidental reverse connection or short circuit. Well when I connect or disconnect the negative clip from the earth on the car and before I turn on / off the mains input there is always a spark. Is this a fault that I should be concerned about? The man I spoke to at the shop was not sure what to say apart from saying that all their chargers only have 2 pin mains plugs. I'm no expert by any means but that doesn't sound right, especially if the charger is still not plugged into the mains.
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Post by Deleted on May 4, 2020 22:36:52 GMT
Hi firemac, yes I am on the side of it not being perhaps 100% correct so as soon as I am allowed to go to the shop I will take the charger and show them. I will ask for them to try one of their chargers and see if the same happens. It has a 5 year warranty so I am not worried about costs.
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Post by shcm on May 5, 2020 7:13:30 GMT
I have just purchased a small 9 stage battery charger just to keep the battery topped up. The handbook says the charger must be plugged into an earthed or grounded mains socket. The plug supplied with the charger doesn't have an earth pin, it only has 2 pins. You have to connect the charger to the positive battery terminal first and then a suitable earth on the car before connecting the charger to the mains. It says it has polarity protection which prevents the output leads from sparking due to accidental reverse connection or short circuit. Well when I connect or disconnect the negative clip from the earth on the car and before I turn on / off the mains input there is always a spark. Is this a fault that I should be concerned about? The man I spoke to at the shop was not sure what to say apart from saying that all their chargers only have 2 pin mains plugs.
The earth is effectively irrelevant as far as charging the battery goes. If the charger has a metal case, then it is cause for concern (i.e. in an fault condition, where the case could become live, e.g. internal wiring becomes loose). Otherwise if the case is plastic, it's less of a concern. I'd probably use either a plug in RCD (circuit breaker) or RCD type socket with it anyway, then you have a little more protection.
On the battery end: For a spark to occur, you have to initially generate a high potential difference (voltage) by some means - higher than the air breakdown voltage (and that varies. Nominally 30kV/cm but 20 to 70ish kV/cm is possible). Anyway, a lot higher than a 12Vish associated with a car battery. How would you get a spark?
Well:
1. The potential difference between the car and charger could be that great (well, I suppose a static type charge is possible, in some scenarios)
2. Lead inductance combined with the rapid change in a current flow, will produce a momentarily high voltage. (Remember Faraday's Law from school? E=-L dI/dt?). While the lead inductance will be low, (assuming you haven't wound the leads around some ferrite material lots of times) if you suddenly stop (or start) the current flowing, dI/dt can be huge. Then, it doesn't take much inductance (like lead inductance) to generate a very high voltage.
To some extent, you can play tricks with resistors and capacitors around this, to limit any spark.
Why would there be any current flowing when you connect/disconnect a well designed charger that is off? Basically, I'd want to know what current was flowing into/out off the charger and for how long when you connect/disconnect the charger. You'd hope very little with a charger that's off (There may be a little inrush current into the charger, charging any capacitors that may be across its output). Otherwise, in that off state, it's probably discharging the battery to some extent.
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Post by Deleted on May 12, 2020 5:54:10 GMT
Here is a short video showing the sparking when I connect the charger to an earth. The mains power feed is not plugged into the mains.
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Post by shcm on May 12, 2020 7:29:49 GMT
The charger ground and chassis ground are probably at different potentials (maybe static charge build up) before you connect. To prevent the spark, you need some means to equalise the charge (or keep the two grounds at or near the same potential). Yes, maybe a mains earth would help, but there's no guarantee the vehicle chassis earth/ground/-ve is also at or near the same potential. ESD (Electrostatic discharge) protection (this is a big area in electronic PCB and semiconductor manufacture and others) is usually done by keeping various things (mats/benches/people) "connected" via a dissipative materials (or a very high value resistance if you like). Mains earth is very often used as the "common" point, but different benches/mats/etc are all connected to the "common", via resistances in the megaohms range. A low resistance "direct" connection can be just as dangerous, if the path should become live in some way. A high resistance path allows any charge build up to equalise (or discharge/dissipate to ground) without being dangerous (a large current is prevented from flowing and it's current that ultimately kills you). What *might* stop connection spark, is connecting the charger lead to chassis ground via something that's high resistance first, for a few seconds, before connecting the charger lead directly.
(Remember, the term "ground"/earth can be confusing. There is never really any one "absolute" ground/earth only points that are at the same or different potentials. Mains earths are mostly the same potential-ish)
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