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      11-22-2020, 01:42 PM   #23
HighlandPete
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Originally Posted by dizzy619 View Post
If you have an f31 it is way more messing about doing it straight to the battery believe me...
At least for charging, there is absolutely no need to get to the battery itself. Makes it so simple to charge from the front jump start terminals.

As to the running SoC, what ever we do with a smart charger, the energy management will not hold a 100% SOC in use, it will let the SoC drop to around 80%, before changing the charging phase. Purposely leaves capacity for over-run energy harvesting.
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      11-23-2020, 02:46 PM   #24
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Originally Posted by NanasBack View Post
The official BMW guide, as listed in earlier posts, is to "connect a battery charger to the jump start points under the bonnet.
This allows the IBS to monitor the charge state of the battery".

People should follow BMW guidelines.

However, I believe it is better to directly connect the charger to the battery terminals as long as it is suitable for AGM batteries.
(Assuming there is an AGM battery fitted).

The following explains why. Skip it if your not interested


BMW Efficient Dynamics.

The car braking system is used to slow a vehicle down and looses energy in the form of heat, dissipated by the brake discs & pads.
Some of this energy could be used to charge the battery, in the form of regenerative power.

The Intelligent Battery Monitor system is used to protect the battery from over charging.
The battery capacity must be registered with the IBS system, in order for it to monitor how much energy can be dumped into the battery, without over charging it.

The IBS system uses a 70% charge target for the battery. (70% charge of the battery capacity rating).
Regen braking can use the 30% available capacity to dump energy, reducing brake disc & pad wear.

The IBS also has a derating curve for the battery age and reduces its capacity rating accordingly, again to prevent overcharging.

The problem I see here is, there is a likely safety factor, used to keep the values on the low side to ensure no overcharging occurs.

So the battery capacity will be under-rated.
The aging capacity reduction will be over estimated
(There's probably a temperature derating function and maybe others).

All leading to the battery capacity being well under estimated.

The biggest killer of lead acid batteries is under charging.
This leads to sulphation.

So the principle of keeping the battery at a nominal charge of 70% is not doing it any favours.
In reality, it's problably kept at a level of charge significantly less than its actual capacity.

Using the under bonnet terminals for charging allows the IBS to monitor the energy the charger puts into the battery.
It'll adjust what the car alternator puts into it on subsequent journeys and likely well under-charge it again.


So, get on those battery terminals. Charge away!
I do.
Some very valid points. I am not sure I agree with charging the battery directly. I toast an IBS by doing that. So the best thing to do is disconnect the IBS carefully and then connect to the battery.
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      11-23-2020, 04:11 PM   #25
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Originally Posted by Soul_Glo View Post
Some very valid points. I am not sure I agree with charging the battery directly. I toast an IBS by doing that. So the best thing to do is disconnect the IBS carefully and then connect to the battery.
I'm not seeing how charging directly to the battery helps at all.

From my perspective it could be more risky, chance of arcing or shorting while connecting. As to the life of the battery, how is it saving it?

BTW, my battery is going into the 10th winter (not sure how much longer I can expect it to last) and that only gets a 'top up' from the front terminals.
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      11-23-2020, 04:17 PM   #26
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Perhaps I should have mentioned, the charger I use is of the 'maintenance' type.
Maximum output is 2 amps - designed for topping up and 'float' charging.

If you need to connect a rapid charger for a flat battery, maybe you would be better off disconnecting it.

But BMW still say use the under bonnet jump start connection for this.
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      11-23-2020, 04:19 PM   #27
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Quote:
Originally Posted by HighlandPete View Post
Quote:
Originally Posted by Soul_Glo View Post
Some very valid points. I am not sure I agree with charging the battery directly. I toast an IBS by doing that. So the best thing to do is disconnect the IBS carefully and then connect to the battery.
I'm not seeing how charging directly to the battery helps at all.

From my perspective it could be more risky, chance of arcing or shorting while connecting. As to the life of the battery how is it saving it?

BTW, my battery is going into the 10th winter (not sure how much longer I can expect it to last) and that only get a 'top up' from the front terminals.
I use the dedicated terminals as well I should add. I was actually seeing less charge when connecting via the IBS and battery. Around 12.6v-12.8v with a CTEK. Via the terminals it's around 13.2v. It's easy to damage the dainty IBS. What I was saying was if someone wanted to connect directly to the battery they'd be better off removing it or disconnecting things to charge it. My F30 made 8 years on a Bosch S5. There were plenty of aftermarket additions. Dash cams, parking batteries, tracker, alarm...
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