TDI Battery Problems: Too Small?

Hello,

As a side topic to https://community.dieselschrauber.org/en/viewtopic.php?t=23690, I'm interested in knowing if anyone has ever installed/had to install a battery that was actually too small into a TDI because the normal size wasn't available:

What is the normal size (in Ah and cold start current) that is specified for the vehicle?

What size (DIN type or Ah and cold start current) did you instead install?

What problems did the undersized battery cause, and under what conditions?

Background: I am looking for ways to reduce weight, and I see potential for saving some weight, possibly around 18 kg, from my battery.


Okay, please provide the German text you would like me to translate into English. I will only provide the translation.
I once browsed through Moll's car registration database.
http://www.moll-batterien.de/produkte.html -> Mapping list for passenger cars.
And lo and behold, some 1.9 TDI engines from the 90s only have a cold start current of 40Ah and 360A.
Passat Variant (1988 - 1997) and Polo Classic (1995 - 2001) -> Battery type 540 045 036, where the last group of numbers indicates the EN cold-cranking current (multiply by 10).

For example, a battery with specifications of 55Ah / 420A was approved for the Ibiza 6K1 (1993 - 2002) -> Battery type 555 065 042.

According to this, it seems that all the variations in battery size are due to the power-hungry vehicles of today. However, since I have already put my Ibiza on a "no-comfort" diet , I am confident that it should be able to manage with such a small battery .

Am I wrong about this? If so, why?

Since I've already put my Ibiza on a 'no-comfort' diet, I am confident that it should be able to complete the laps even with such a small battery...


Let me put it this way...

'Please let me know in advance which route you're taking so I can go a wide detour around it.'


Your plan would only work with the simultaneous expansion of:
- Climate (okay, it's already planned, so no problem).
- Servo (might be difficult to get approved for).
- ABS (Not applicable/Not possible).
- ESP (NOGO)
- and the complete airbag and seatbelt pretensioner system (NOGO).

function.

These systems still require sufficient safety margins from the battery even at -40°C. It may seem excessive, but with the smaller battery, you won't achieve that reserve even at -10 or -15°C. And those are more realistic conditions, even for Germany.

Electrical systems today are significantly more sensitive than commonly believed. The battery is the weakest component in this regard.

From my perspective, the larger battery size is also related to the pre-glow and post-glow phases. With the new emission standards, the afterglow period is longer, and in some cases, even the coolant is heated by glow plugs, which requires a significant amount of electricity. The air conditioning system probably doesn't make that much of a difference (except for the occasional additional cooling fan).
I'd like to estimate how much electricity you might use in the winter for things like lights, ventilation, rear window defroster, and glow plugs.

"Ulf has the heating under control...the interior heaters are turned off, and to protect the GSK (presumably a piece of equipment), I once read that you should disconnect it as well (especially in summer)."

The afterglow could indeed be a problem initially. I remember the 1.25 DDIS (also known as 1.3 JTD) in my previous Suzuki Ignis DDIS, which suffered from reduced power due to glow plugs failing in extremely cold conditions during city driving, but they wouldn't switch off for ages...

Theoretically, this energy requirement should be completely covered by the generator, right?

Holger247 wrote:

I would like to do a rough calculation of what you need in the winter for lighting, ventilation, rear window heating, and glow plugs.

After a more detailed private message conversation with Goettmann, I mainly did a cold start calculation (including preheating). The lights, etc., are covered by the alternator (120A).
While Goettmann considers battery capacities below 55Ah to be risky and a waste of money due to rapid battery degradation caused by daily starting loads, I was able to get a 45Ah / 450A "Cartechnic UP45" battery from Stahlgruber for around €56.
Regarding the cold-cranking current as a primary critical factor, I am "only" sacrificing 17% of the factory setup (70Ah / 540A), and the battery weight of 11.83 kg is reduced by 36% compared to the usual approximately 18.5 kg . I couldn't resist it .

The UP45 performs exceptionally well even during a cold start...
If it fails prematurely, only a relatively small amount of money will be lost.
In addition, the previously used, fully functional 75Ah battery is available as a backup to prevent the voltage of the UP45 from dropping to levels that could damage electronic components during startup.

Oh yeah: Even when used as an EU4 tractor, the BUK will only glow for a maximum of about 90 seconds.
If the on-board voltage drops to the battery discharge range while the engine is running, the idle speed will automatically increase to approximately 1100 rpm, where the 120A alternator already provides a significant amount of power. If that is still not sufficient, less critical consumers (e.g., rear window heater) will be switched off.
This effectively eliminates the risk of completely draining the battery, and thanks to the almost always available 14.4V, it ensures the fastest possible battery charging after starting.

56€ for a 45... that would be too expensive for me.



Sure, I'll try.
You are aware of the risks and can take corrective action in time.
As you already mentioned... it's worth a try.


Greetings from Goettmann... who is currently stranded with a company car that has broken down...

goettmann wrote:

who is currently stranded with a company car that has broken down...

...because of a too small battery or something like that???

goettmann wrote:

56€ for a 45... that would be too expensive for me.

Not everyone has access to your material sources.

Quote:

But try it. You are aware of the risks and can take corrective action in time. As you already said... it's worth a try.

Everyone has the right to their own belly landing.

Yesterday, after driving home and having at least 3 semi-warm to warm starts of the 1.9 engine, I connected the UP45 to a voltage-regulated charger (14.4V) in order to fully charge it and thus obtain a defined starting state for future observation of its condition (I can skip the acid density check because this thing no longer has screw caps ).
After the normal power surge when connecting the charger, the current dropped, but then remained stuck at approximately 4A, without the indicator visibly decreasing further – which made me a bit concerned.
Over the next few hours, the charging current gradually decreased further, and this morning, after approximately 12 hours of charging, the indicator showed about 0.1A, which is what you would expect for a brand new battery.

Probably, it took so long to compensate for the self-discharge during storage: Somewhere , I read that energy slowly drawn from the battery can only be recharged slowly for physical reasons (without overcharging with high voltage), and this would explain the observed charging current pattern.


The engine started normally this morning at around 15°C, just as expected with the 18kg battery.
I know: it's only in the winter that it really gets going with preheating, but every cold start with the usual starter motor speed increases my confidence until then .

In the near future, I will regularly connect the small battery to the charger in order to monitor its condition, at least based on the charging current. If it fails prematurely, you will find information about it here.

I had a 55Ah Optima Yellow battery in my C4/4B with a 2.5 TDI engine for 5.5 years. However, this small but powerful battery is not only expensive but also relatively heavy, so it's not suitable for the intended purpose.

Hello Ulf,

Your plan is borderline. I'll send you more details via private message.

If it's possible or desirable to forgo the use of reserve current for cold starts, I don't see any problems with that.
However, it is important that the charging profile ensures a complete charge after each start-up process.

Disadvantages:
- no reserves in electricity supply.
- shortened battery life due to the tendency towards harmful deep discharge of the battery

by the way:
Personally, I would always install the largest battery that my budget and the available space allow.

Regards,
t.klebi

Hi there,

I also share goettmann's concerns about the lifespan of this battery. Not only is the depth of discharge, which is crucial for its longevity, higher than ideal, but frequent charging to the gassing level in a sealed battery can be detrimental because some water loss is inevitable, even if recombination vents are present.

Hi,

Quote:

For example, a battery with specifications of 55Ah / 420A was approved for the Ibiza 6K1 (1993 - 2002) -> Battery type: 555 065 042.

I'm glad my e-bike has a built-in battery system instead of relying on external batteries like this one. I believe the savings from a few kilograms less weight are insignificant compared to the cost, material usage, and energy expenditure required to acquire a new battery. Furthermore, such a battery would likely have a significantly shorter lifespan and need to be replaced sooner.

By the way, my 70 Ah battery (Varta, manufactured in mid-2001) is still working great after 156,000 km. It even managed to start the TDI engine in the second-to-last winter, despite three faulty glow plugs, and it also coped well with the long winter last year, now that the glow plugs were working again.

For comparison: The 44Ah battery that my father had in his Passat 3BG (1.8T engine) was dead after three or four years. The only advantage of that battery was that it could be lifted out of the car more easily than the heavier 70Ah replacement.

Best regards,

January.

Roger wrote:

I also see that goettmann questions the lifespan of this battery. Not only is the depth of discharge, which is crucial for its lifespan,

higher than expected. Of course, I don't think a TDI engine that mostly ignites on the second compression is much worse here than a gasoline engine with a significantly longer cranking time...

Quote:

With a sealed battery, frequent charging up to the gassing range is often unhealthy because some water loss is always to be expected.

Even if recombination vents are present. I do not charge it up to the gassing range.

My charger has a voltage limit of 14.4V.

2. According to the product data, the battery is suitable for vehicles with a higher voltage regulator output (presumably 14.8V).

Jan6k wrote:

I think that the savings achieved by having a few kilograms less weight are not proportional to the need to acquire a new battery (cost, material and energy expenditure), which is very likely to have a significantly shorter lifespan and therefore needs to be replaced sooner.

It may not necessarily be financially worthwhile, but that's not what I'm concerned about.
My main goal is the (minimal) weight of the carriage, and a difference of 6 kg is already a significant amount .

With a sealed battery, frequent charging up to the gassing level is often unhealthy, as some water loss is always to be expected.
Isn't it perfectly normal for the battery to be charged frequently up to a voltage of just under 14 volts? Surely, the smaller battery isn't being charged more often than the larger one, right?

If Ulf only drives long distances and the small battery provides a high cold-cranking current despite its small capacity, I wouldn't be worried about any problems.
It only becomes problematic when the charging time (driving time) is insufficient. The reduced state of charge of the battery leads to increasing sulfation, which ultimately results in premature failure.


Regards,
t.klebi