Cranking speed

P

paulwornell

Active Member
Joined
30 May 2001
Messages
46
Visit site
Simple question - would I get faster cranking speed from an engine start battery rather than the leisure battery I have installed. The VP 2001 churns slowly and for ages before she eventually fires. Then runs fine once battery has recovered. Full cold start procedure understood and operated.
 
Hi,i dont think it does a leisure battery any good using it as a starting battery,i think they are designed for a slow discharge rather than the short sharp blast required to start your engine.

the slow cranking speed could be that it is knackered.

my last boat had a VP2001 and i used an ordinary car battery as a dedicated starting battery it was ok and started the engine 3rd go in winter.
 
Last edited:
Woops you are lucky that the battery still has a charge! Buy a cranking battery, that is one meant for the job. Car battery about 70 amp should do it. A starter battery is built to give a full load immediatly and charge at a very fst rate. Whereas a deep cycle battery will only give of a slow low charge and is recharged slowly. Hope that helps'

Peter
 
Other considerations are cable sizes; grubby contact at the end of the cables; sate of the current leisure battery.

A leisure battery in itself should not necessarily produce a difficult start-up. What does the manual say about a minium spec?
 
Pye_End said:
Other considerations are cable sizes; grubby contact at the end of the cables; sate of the current leisure battery.

A leisure battery in itself should not necessarily produce a difficult start-up. What does the manual say about a minium spec?
Click to expand...

I almost always start my engine using my domestic, leisure type batteries. Until very recently my starter battery was also a leisure type, which is how Sadler built it. I have experienced no reduction in battery life due to this, and as just written on another thread, the last set of batteries lasted 8 years and the present ones are 4/5 years old.
 
Some leisure batteries have a CCA rating marked on them some do not.

I am tempted to deduce that some may be more suitable for starting than others.
 
Have had similar symptoms due to a tired starter motor. New motor with same batteries almost doubled cranking speed.
Would suggest a first step is to borrow a car starter battery of suitable capacity and see if there is a difference with cold starting. This will help identify source of problem.
 
Have had similar symptoms due to a tired starter motor. New motor with same batteries almost doubled cranking speed.
Would suggest a first step is to borrow a car starter battery of suitable capacity and see if there is a difference with cold starting. This will help identify source of problem.
 
paulwornell said:
Simple question - would I get faster cranking speed from an engine start battery rather than the leisure battery I have installed. The VP 2001 churns slowly and for ages before she eventually fires. Then runs fine once battery has recovered. Full cold start procedure understood and operated.
Click to expand...


How old is your 2001? I believe Volvo modified the starters as used on the early engines as they did crank too slowly. Possibly they changed the gear ratio in the starter. However ignoring this you will find that some leisure batteries such as those sold in caravan outlets and some marinas are only suitable for deep cycling on low loads and will give a short life if used for cranking diesel engines.


Check your battery and see if it gives a cold cranking capacity and also check
all connections are good .
 
Before worrying about the battery

Here's what I'd do: Using a test meter (if you haven't, get one - they don't have to cost more than a pint or two - for example.)

1. The battery terminal connections can give trouble, even if they look OK, so I'd clean them anyway - a bit of emery cloth on the terminals and the connectors will do the job.

2. Measure the voltage across the battery terminals at rest then while cranking the starter. A rest voltage of less than about 12.5v suggests a problem. There'll be some voltage drop when the engine's being cranked, but a cranking voltage of less than about 9.6v suggests the battery may not be up to the job.

3. Check the voltage between the + on the battery and the terminal on the solenoid. A drop of more than a fraction of a volt indicates a problem, so investigate further, connection by connection - batttry terminal to cable, isolator switch, etc. Now do the same on the earth side to the negative battery terminal. Clean and remake any iffy connections. I had a problem with my isolator switch, which I "cured" for testing purposes by connecting both cables to the same terminal on it. My cranking speed immediately doubled and suddenly the engine was starting properly! If the copper strands of the cable are blackened rather than bright copper, it's probably time to replace them - the bigger the better within reason

4. Once you know all's well in the connections, you can check the drop across the starter solenoid, which, again should be minimal. If not, you may be able to clean the contacts inside, or you may have to replace the solenoid.

5. Last resort: take off the starter and get an auto electrician to check it for you.
 
There are three types of battery: Automotive starter batteries, Traction batteries, and leisure batteries. Auto batteries are designed to give a hefty amperage for starting a 'big' engine i.e. 4 or more cylinders , or diesels with their higher comporession, which may need anything from 300 to 600 amps to start them (more for a big diesel, but usually they then go to 24 volts or more to keep the amperage down). They are intended not to be discharged below about 70% capacity, then to be topped up again straight away by the engine charging system. Deeper slower discharging damages them and reduces capacity. Steady low amperage discharge will cause them to drop voltage quite rapidly and at around 70% the voltage will be dropping off quite rapidly.

Traction batteries - sometimes sold as leisure batteries - are designed to be able to give a fairly hefty 'starter' current, but also withstand long periods of discharge to around 50% without damage. These are typically used in electric fork lift trucks, mobility scooters and such like, where they may be run to near depletion before being recharged. Most of them will sustain starting a medium sized engine regularly, and will maintain an adequate voltage throughout the discharge cycle down to around 50% capacity

Leisure Batteries are constructed to maintain a good steady voltage on slow discharge and to be used as 'domestic' batteries for running lights etc. The internals will overheat, warp and become damaged if used for extended cranking of anything but a small marine petrol engine. They will quite happily start smaller outboards up to around 500cc (25 -40hp)for example. They will maintain a good voltage to a very low state of charge, so that your 'battery voltage meter' may well give a very optomistic reading of the actual remaining charge compared to an auto starter battery, and may still be giving useable voltage as low as 40% capacity in a good one.
 
Thanks to all - now more detail

Many thanks to all posts and will try checking voltages and connections as suggested and after that substitution. Just to answer a couple of questions firstly I am using a new 1kW PMGR replacement starter motor which is a fairly widely advertised replacement for the original 0.8kW Hitachi and which I understood would give faster cranking (because of the gearing). The battery, also new, is described as a dual purpose starting and deep cycle battery boasting 100AH and 600 CCA's. Further observations welcome.
 
600 CCA is more than enough for a VP2001. If that battery is performing to spec it's not what the problem is. You say it's new - have you given it a good charge since buying? It's not unknown for "new" batteries as bought to be at quite a low state of charge. Depends how long it's been in stock without recharging. After 6 months it might be down to 50% or less depending on temperature and the quality of the battery. That should be recoverable but shouldn't be used without a thorough charge.

My VP2002 has a 60Ah car battery which is probably also around 600 CCA and it's more than enough. My 2 litre diesel car engine has a battery not much bigger.

It's generally a myth that "leisure" batteries will be destroyed by normal engine starting. "Leisure" doesn't mean anything specific, but mostly they use truck starter battery plates with different separators. They will have a lower CCA because of higher internal resistance and slower electrolyte diffusion (because of the different separators and possibly increased inter-plate spacing). CCA is usually measured over 30 seconds (which is a VERY long crank). The heat produced in that time through the ohmic resistance of the battery is easily dissipated in the mass of lead initially, from which it goes into the electrolyte by convection.

The voltage at end of discharge - and the capacity - is related to discharge rate. The 30 sec CCA will be to 1.6 or even 1.5 volts per cell. On an 8 hr discharge you shouldn't go below about 1.8vpc. It isn't that the "leisure" battery maintains its voltage better; again it's mainly down to internal resistance and acid diffusion.
 
You must log in or register to reply here.

Share this page

Top