Can anyone quote a "Vehicle cranking current" for their TR?

[john.r.davies]

A recent forum Q. was for battery recommendations, and it was met by specific and helpful suggestions, from members who had had success with an Xbatt 12345, a Yfire 431, or whatever. Fine, and just what the forum is for!

 

But the real question should be, what is the "Vehicle cranking current" for my TR, so that I can match the battery I buy to its needs? That value, the VCC, is quoted by every modern manufacturer for each model, if you look for instance in 'AutoData', and is the current the starter will draw to turn the engine sufficiently fast to start. It'll be in the region 120-180 amps, depending on the engine's size, compression etc.. With this knowledge, any battery you buy should have a greater "Cold Cranking Amps", a value that will be in the battery specs. This is not the same as the Amp/hours!

 

But AFAIK, Triumph never quoted a VCC for TRs. Does anyone know what they are?

 

JOhn

 

[Lebro]

I have a clamp on ammeter which could be used to measure - I can do that on my '3 if you like.

I have the standard "Bomb" starter motor.

 

Bob.

[john.r.davies]

"Clamp on"? That's the style that measure current by induction?

I fear that few will have an instrument that could measure so much current directly.

 

Yes, please, Bob - it would be good to collect this information for all models.

JOhn

Edited October 17, 2014 by john.r.davies

[Lebro]

OK will look at doing that today (after I replace my carpets (see other post !)

 

Bob.

[AlanT]

Be interesting to do this.

 

I am going to guess that the figure will be nearer 180A than 120A.

 

I have a feeling it may go over 200A.

 

It's just a guess though, I've never measured this.

[RobH]

My '3A has a modern geared starter. I've just measured the current as 174 amps from dead cold. A standard starter will take quite a lot more than that, possibly in excess of 250 ?

 

Rob

Edited October 18, 2014 by RobH

[Lebro]

Hmm Interesting, just measured mine (TR3 with "Bomb" starter motor.)

Engine cold (well 19°C - current outside temp) 130A once turning, engine was spinning over really quite fast.

The instantanious initial current is obviously much higher, but hard to capture this without a storage scope !

Now maybe my compressions are not what they were, & I do have a very good battery, but this was lower that I expected.

 

I have no reason to suspect the meter of being innacurate.

 

Bob.

[RobH]

Very interesting Bob. Just to make sure I checked again - things have warmed up a little and this time the current was 160 amps at normal cranking speed. My meter is a fairly cheap Maplins one so I have no idea of its accuracy but it seems to read correctly on other ranges. the car hasn't run for about a week so there might be some bearing drag I guess. I'll do it again tomorrow after I have run the car.

 

Rob

[Rodbr]

I viewed the issue like buying for a large Outboard 115hp

I used 100 amp with 750 -800 cca (cold craNKING AMPS)Never given a moments issue.

Tend to be the size as the battery tray on a TR

[john.r.davies]

Thank you!

Bob - TR3 - 130A

RobH - TR3 - 174A

 

BIt of a gap there I can't explain.

 

What about other models?

 

Once you know the VCC, then selection is easier, as the battery should quote the Cold Cranking Amps, defined as the current it can deliver, at 0F (-17.8C), for thirty seconds, without the volts dropping below 7.2V. It must not tbe confused with the "Cranking Amps" figure which only applies at 0C in far more generous conditions.

 

Rod, even a 115hp outboard may not be comparable, but a CCA of at least 20% more than the VCC should be sufficient.

 

JOhn

 

 

 

Edited October 18, 2014 by john.r.davies

[ianc]

A greater current will be drawn with the original starter motor, but a geared motor will turn faster and draw somewhat less.

According to my records, I fitted a Kwik-Fit battery in 2002 (4-year guarantee) and a geared starter motor in 2005.

I never use a battery charger/conditioner, but use the isolator switch whenever the car is static. The car is used in the winter as long as the roads are free of salt & grit - salt-free water is not a problem!

The engine is 2238cc and the compression ratio is around 10.0.

Ian Cornish

[Lebro]

Just to confirm my measurments, I have repeated them placing the clamp in different places -

1 over the cable to starter motor

2 over the cable from battery to solenoid

3 over the cable from battery to body

 

all gave the same reading.

I have seen up to 150A initial current, but always drops to 130A give or take 5A

My meter (RS stock 243-0655) claims an accuracy of +/- 2.5% +2A

 

Bob.

[ianc]

Bob - once the solenoid has been activated, the current required to hold it in will not be great, so the extra current that is flowing from battery to body (your measurement 3) would be difficult to detect.

The weather is very mild at the moment, so it would be worth repeating these measurements when the ambient is around zero Celsius and the motor churns more slowly - I would expect a reading nearer 200 amps under such conditions.

Ian Cornish

[duncan]

I just got the biggest brute that would fit in the battery tray, always works for me - touch wood. I will check the battery size when I get home.

[Lebro]

FTR I am using a Yuasa 086 size from my local car spares shop (Camberley Auto Factors)

 

Bob.

Edited October 21, 2014 by Lebro

[RdeJ]

Would be interesting to know/compare he voltage drop over the battery.

Guess to see

- Good battery condition: low voltage drop, less current

- Bad battery condition: high voltage drop, high current

(W=UxI)

 

Robert

[Lebro]

Other way round me thinks

[littlejim]

Fascinating thread with some new (to me anyway) info.

From the battery ignorant standpoint, I just got one about the same size and capacity as the old one. because it cranked the car i assumed it had enough capacity.

 

After that it is a matter of looking after it. Those with daily driver TR s probably can forget about it after fitting.

Mine sits like Buddha in the garage for long periods and the battery gradually fades from peak performance.

 

For some time I used a big charger to top it up, but now I use one of those small 'smart?' chargers from places like Tandy, (or here Jaycar) that can stay connected 24/7 without boiling the water off. (Still pays to check periodically.) She's hot to trot whenever I want to use it.

[RobH]

The battery capacity is only part of the story - in order to provide high current without too much volts drop the battery needs to have low internal resistance which is where the 'cranking current' rating comes in that John asked about. The capacity only tells you how long it can do that for. i.e. a 65AH battery can in theory provide 6.5 amps for 10 hours or 65 amps for one hour or 650 amps for 6 minutes. In practice the battery internal resistance means that as the current goes up, the voltage goes down so that if you tried to pull 650 amps the battery voltage would probably drop right off to an unusable value. The volts are important because that is feeding the ignition circuit. If it drops too low the spark may be too weak to fire the engine.

You need to have a battery which is suitably rated to provide a the high current as well as the required capacity. Just because a battery is a bit discharged it does not mean it cannot provide cranking current - it just will not be able to do it for so long and the volts will be a bit lower.

 

Not all batteries are the same. I have a vintage car which has a 6v electrical system and when I bought it it would just about turn over on the starter despite the PO having fitted two extra-large batteries in parallel to try to cure it. The problem was that the batteries he used were general-service types not designed for automotive use. Although they had oodles of capacity, they could not provide the very high current required for a 6v starter without the voltage dropping right off. I fitted the right kind of battery which has about half the capacity of those two but high cranking current ability and the motor now churns over as fast as a modern car.

 

Sorry to go on at such length but there seems to be some misunderstanding out there.

 

Rob

[RobH]

I've just checked the current again with the engine warm - 125Amps (geared starter)

[AlanT]

One of the reasons I expected the current to be high was that I expected use of 20/50 oil which is quite thick compared to modern usage.

 

Also holding down the clutch while cranking will reduce the current. I reckon you want about 300W to spin a cold transmission.

There's another experiment to do on a cold day.

 

The internal resistance of the battery will limit the initial transient current because a stationary motor is basically a "short-circuit".

As it spins up it kind of generates so as to reduce the current it takes.

 

The motors don't provide enough torque to spin a cold engine very fast and so the current they take is greater.

 

In the 70's I had a Leyland 1300, I ran out of petrol more or less outside a petrol-staion but it was on the other side of the road. Quite a busy road.

 

I engaged 3rd gear and drove across using the starter motor. I have never run out since!

Edited October 19, 2014 by AlanT

[littlejim]

Thought I'd through (ough=ow) this in.

 

http://www.dcbattery.com/faq.html

Edited October 21, 2014 by littlejim