To all the boffins

Can anyone tell me what the maximum permissible voltage you can put into the battery.

12V battery Alternator puts out 14.8v when running .
Can you put 18v in off a charger I.E solar charger plugged into the rear 12V socket

Thanks in advance  2020 Porsche Panamera Turbo Hybrid (V FAST)
2017 Range Rover Autobiography 5.0 V8
2018 JCW Mini Cooper
2018 Skoda VRS

The battery will only take what it needs.... An 18v solar charger is ideal for 12v batteries. Previously..
Vogue SE TD6
Defender 90 2.4
Defender 110 TD5
Vogue 3.5 EFI

Cheers

will this be ok then

http://www.ebay.co.uk/itm/12v-10w-or-30w-S...33870ff670 2020 Porsche Panamera Turbo Hybrid (V FAST)
2017 Range Rover Autobiography 5.0 V8
2018 JCW Mini Cooper
2018 Skoda VRS

Yes, but that's expensive.... I got mine in a maplin sale and I don't think I paid £30.. Previously..
Vogue SE TD6
Defender 90 2.4
Defender 110 TD5
Vogue 3.5 EFI

Your one is 70 quid now in Maplins
I need a sale  2020 Porsche Panamera Turbo Hybrid (V FAST)
2017 Range Rover Autobiography 5.0 V8
2018 JCW Mini Cooper
2018 Skoda VRS

Not necessarily the case;

When using a very small charging source like a 1-5watt solar panel, on a battery that is fairly large, used on a vehicle with an almost constant current draw, will be just fine. The reason being the charging source is so small and weak in comparison to the battery it is trying to charge that it could almost never over charge the battery, even if left in the sun, on the equator at midday.

If the charging source was larger, then a regulator of some description will be required to ensure the voltage is regulated at charging voltages. These charging voltages change with battery type.
Common lead acid batteries 14-14.6v is usually the recommendation
Gel batteries Max of 14.2 is usual with gel cells
AGM batteries 14.4-14.8

If you over charge a battery you will shorten its life. The manufacturer will always recommend which voltages should be used for each stage of charge.

Normal alternators are whats known as a 'constant voltage variable current charging system' this means the voltage regulator is preset to charge at a given voltage (decided by the vehicle manufacturer, usually between 14-14.4 volts) The current fluctuates as the battery charges. A deeply discharged battery has very low internal resistance so it is easy for the alternator to push in lots of power. As the battery charges the internal resistance increases and thus, the charge rate (current) drops down. This is great, and gets us to 80% state of charge (SoC) in the shortest time possible. What it cannot do is fully charge a battery to 100%, when the battery gets to around 90-95% SoC the resistance is so high the voltage regulator basically says 'thats too high, it must be charged, I'm going to shut down' and this is what stops your batteries becoming over charged.

Advanced charging systems do it slightly differently, they'll replicate the above and give it the term 'Bulk Charging' this bulk charging is stopped by processors when the batteries get to around 80%, at which time the charging system will drop into its absorption stage. This stage is designed to get the batteries to 100%. This stage can take as long as the bulk stage to complete. The voltage is reduced slightly (if bulk was 14.4 absorption may be 14.1/.2) the current level is calculated by the charging and based around how the batteries received their charge during the bulk stage. This gets the batteries to 100% SoC.

Following this stage advanced charging systems can drop in to a 'Float Mode' this float mode is designed to compensate for battery self discharge over time. The voltage will be reduced further (down to 13.3 +/-) the current will end up being less than 3% of the batteries total capacity and will continue to trickle charge the batteries indefinitely.

Some charges then move in to a Power Supply stage, whereby you can power loads around the vehicle without flattening the batteries. Fridges are good examples of this. You can power any equipment up to the rated capacity of the battery charger, your batteries remain fully charged until you disconnect the charger.


So looking at the OP, when using a small charger such as a 3watt plug in through aux socket solar panel, you'll be fine without a regulator. If you want to connect up a larger solar system, or use a larger charger of any sort, it will need the correct voltage regulation.

If anyone has any questions about batteries, charging systems, flat battery protection, battery monitoring etc then please let me know - I can bore you all for days if not months!

Matt

very comprehensive info Matt, thankyou..

Am excellent description from Matt.

Would there be any danger when charging with 18 volts of frying some of the more sensitive electronics the car has?

Hi oldcro, the 18v ( to 21v ) marked on solar panel specs is the OPEN CIRCUIT voltage rating and really has little to do with it’s actual operating voltage.

If you use an unregulated solar panel, as Boat.Buoy posted, the battery actually self-regulates the voltage of the solar panel, based on both the size of the battery and the state of charge of the battery.

To charge/maintain your cranking battery, because of it’s size, you can go as large as a 10w solar panel and not need a solar regulator.

If you use a larger, unregulated solar panel, you will cook your battery way before you do any damage to any of your vehicle’s electrics or electronics.

All modern vehicle electronic devices will are designed to tolerate at least 18v and this is done because of a problem that use to be fairly common but is rare these days, and that is the high voltage caused by a “runaway” alternator.

This is a situation that can occur if the regulator fails and the alternator goes to full charge voltage of around 18v.

At this voltage, if you are driving for some time, it is common to end up cooking your cranking battery, and if you have lights on as well, you can blow some globes, but none of the vehicle’s electronics will be effected. 2007 TDV8 Lux

Personally I would always try to keep the voltage range between 11-15 as an absolute maximum, most sensitive electronics will tolerate 10-16 volts. Batteries will start to get unhappy from 14.9v upwards.

There is just no way of knowing what damage could occur when voltages get too high. As Drivesafe mentions, if your alternator goes open circuit when your driving at speed (so plenty of current available because you are spinning the alternator very fast) then damage could be quite extensive, and obviously expensive!!

Low voltage can also cause you problems you might not expect; take my Defender. After one trip out I found myself cranking the engine to remove water from the bores (long story..for another day) during this time I obviously ran my starter motor quite a bit. Now I was careful not to over heat the starter motor, only cranking for 30 or 40 seconds at a go before letting it cool and trying again. After some time the voltage dropped, I carried on. Well my starter is (I'm guessing here) 1500watts. To make 1500watts at 14.4 volts you need just over 100amps (104.16667 to be precise) when this voltage drops to 12v we need 125amps to make the same power (wattage) so now my current draw has gone up each time I crank, making the problem worse, faster! When I get down to 11volts I need 136.36amps to do the same job I was previously only giving 104a!? Now you think that might not be too much of a problem, well the tiny terminals inside my starter motor clearly weren't designed to take 100a continuously, let along 136a...so the end result was a burnt out starter motor....which actually meant I had to resolder some wires inside and replace a couple of small bits of copper...but it could've been worse, if it happened to an L322 you can guarantee it would be!!

Matt

I knew you boys would come up with the right answers.

So to clarify.

Buy a 10w 12v solar charger and plug it straight into the rear socket. All will be fine

 2020 Porsche Panamera Turbo Hybrid (V FAST)
2017 Range Rover Autobiography 5.0 V8
2018 JCW Mini Cooper
2018 Skoda VRS

Hi JAYBOY, you’ll be fine.



Boat.Buoy, the reason you MELTED the terminals was not because of the current, typical starter motor current is 300+ amps, in your situation, it was the far too long a cranking period.

Starter motors are just not designed to be cranked for such repeated long periods.

Also, it is commonplace for a even a fully charged cranking battery voltage to drop below 10v while cranking, but it is not likely that you could start or even crank a motor with a cranking battery voltage of 11v.

If your cranking battery was down to 11v before your started to crank, then your would have had a near dead short situation which again would have seriously overloaded your starter motor. 2007 TDV8 Lux

I really don't want to get into the particulars, but when you talk about 300a starting currents you are not talking about a continuous load and the effects are very much different.

You can have a switch with a single continuous rating of 250amps, but that same switch and handle 1250amps of starting current. Handling high current (100a) for a prolonged period of time requires much more heavy duty equipment than starting currents (300a) for a short period of time.

I am more than aware of the potential to burn out, or 'melt' a starter motor and during the whole time I regularly put my hand on the casing and when considered too warm I left it to cool. Yes I would agree starter motors are not designed to crank for long time periods, when it eventually failed, the next morning I stripped the starter motor and found the reasonably heavy duty copper conductors to be absolutely fine, however the small soldered terminals at the top of the casing had become so hot they had let go. There was definitely no melting of any description, all coil coatings and motor internals were in fine condition, and continue to operate to this day, some 5 or 6 years later.

Yes any batteries voltage will drop quickly under high loads such as cranking, but seeing as most people wouldn't have access to the type of equipment to accurately monitor the full voltage range during a crank cycle I was really referring to a standing, off load voltage. I was merely tying to give people an insight into how low voltage can effect current draw, in an understandable manner.

I'm not sure if the modern electronics on these vehicle would even process a start command with a voltage down as low as 11. However a 1986 Defender, with a 200TDi which requires nothing more than turning over with a positive feed to a fuel solenoid is much less fussy, if the engine rotates it'll start..and you would be surprised how low you can take an Odyssey battery and still turnover an engine (providing the electronics will allow it!)

Hi Boat.Buoy I’m not sure what any of your “info” is supposed to be about but your are making assumptions in a number of areas.

For a starter, ( pardon the pun ) but as the battery voltage goes down, the starter motor current draw also reduces, not increases.

The reason the current draw goes down is because the LOWER VOLTAGE applied to the starter motor causes the starter motor to turn slower and therefore draws less current.

Anyone who has ever tried to start a motor that did not want to start can tell you the motor gets slower and slower as the battery is flattened while trying to start the motor.

Further to this point, this is the very reason most automobile manufacturers are LOWERING there operating VOLTAGE. Most DC devices, including DC motors, reduce their current draw as the voltage applied to them drops.

So by the manufacturers lowering the operating voltage of their vehicles, they reduce the current demands being being applied to the alternator, which in turn means the alternator reduces it’s load on the motor, which means the fuel usage is reduces and ultimately, the exhaust emissions reduce.

There are only a few DC devices that increase the current demand as the voltage drops. Inverters are one of these devices. DC motors are NOT.

And yes, after the initial start up current, the continuos current draw will be much lower but once again, starter motors are not designed to run for more than a few seconds at a time, because the continual current draw will damage the motor. 2007 TDV8 Lux

My friend we shall have to agree to disagree.

Simple electrical maths;
1500watt load

1500 (W) / 14 (V) = 107.14 (A)

1500 (W) / 12 (V) = 125 (A)



You lower the voltage, the current goes up. Not down. You are still trying to power the same 1500watt load. Go and try it.

Yes, you are partially right there. The motor does get slower when you are trying to start an engine with a flat battery, not because you are intentionally rotating the motor slower, because you cannot make the correct wattage from your combination of volts and amps - you don't have enough power!

I'm sorry but you are way off here; reducing power consumption based around voltage reduction requires some intelligent power management, load shedding to reduce consumption as power levels drop, this means individual component control, intelligent dynamic monitoring 'most DC equipment' does certainly not include these features! I've not known one starter motor in any vehicle to include this sort of control system. Besides the simple physics behind it doesn't calculate - if you need X amount of power, you NEED X volts and X amps. Anything less and you are coming up short. There is no other option, unless you have some control over physics the rest of mankind is not yet aware of.

"And yes, after the initial start up current, the continuos current draw will be much lower but once again, starter motors are not designed to run for more than a few seconds at a time, because the continual current draw will damage the motor." Now your confusing inductive loads, with starting loads with continuous loads.

A motor has an inductive load to get the motor itself operating. This is generally accepted as 3x the motors continuous power requirement and lasts for fractions of seconds.
Starting current, in this conversation is referring to the current require to start an engine.
Continuous loads, are exactly that, continuous.