car battery voltage volvo 740

[tommy12345302]

Hi
Im going to drive upp to the cold Swedish mountain whit my old Volvo 740 (year 1990). I measure the cars battery and this was the result:
When the car isn’t running (the motor is off) the battery voltage was 12,53
When I started the car while measure : the voltage dip to 10,35 or 10,75 and up again (I had to do it twice because I didn’t pay attention the first time)
And when the car is running the voltage is 14,6

Is this god numbers? The engine is a B230F, there is not a lot of electronic in the car. The batteri is only 2 and a half years old, and the car drives daily

[360beast]

12.53 volts is a tiny bit low but the cranking voltage is good. 14.6 volts is also a good number when charging.

[tommy12345302]

thanks!
I will charge the battery a couple of days before we are leaving. Its below -25 celcius at the place we are going to

best regards T

[Laird Scooby]

As Luke says, good cranking voltages, good charging voltage and a good resting voltage.

One thing to be aware of is if your battery is a calcium battery. Very often these need 14.7V to start them charging and unless you have a "smart alternator" it may not reach it's full charge status.

However, the resting voltage of 12.53V is very close to being fully charged, the charging voltage at 14.6V is higher than a "dumb alternator" (they reach a maximum of 14.4V on a cold regulator and drop to 14V as they warm up) so it suggests you have a smart alternator and a good battery.

Enjoy your trip to the mountains, rather you than me in that temperature!

[kelvinp]

Originally Posted by Laird Scooby

As Luke says, good cranking voltages, good charging voltage and a good resting voltage.

One thing to be aware of is if your battery is a calcium battery. Very often these need 14.7V to start them charging and unless you have a "smart alternator" it may not reach it's full charge status.

However, the resting voltage of 12.53V is very close to being fully charged, the charging voltage at 14.6V is higher than a "dumb alternator" (they reach a maximum of 14.4V on a cold regulator and drop to 14V as they warm up) so it suggests you have a smart alternator and a good battery.

Enjoy your trip to the mountains, rather you than me in that temperature!

That's interesting about a calcium battery, I had to nip down to Halfords today to get a new battery for my 740 and got the calcium one with 4 year guarantee.

Rather odd today, started the car today and drove around the back to load some bags of rubbish for the tip, went to start it and it wouldn't start. I knew it was low on petrol so put a can in but still nothing, yet there was a spark. The battery went flat so I put it on charge, only for about 1/2 hour but I when I put it back it started first time. I have noticed it being slow turning over lately, my only thought was the battery voltage was dropping to low to bring in the fuel pump relay? I didn't have my multi-meter to hand.

Took the battery to be tested and for a 570CCA battery it was only showing 320A so suspect that was the problem. Open circuit voltage was just about OK but obviously didn't have the capacity.

[Laird Scooby]

It sounds very like you have a calcium battery and your alternator is putting out 14V maximum - not enough to charge a calcium battery! What was the off-load voltage of the battery?

[kelvinp]

interesting. Think the open circuit voltage as about 12.5v when they tested it. I've never had starting problems with it before, I didn't have my meter to check cranking voltage and was only presuming that if the voltage was dropping the fuel pumps weren't running

I didn't note whether the battery I took out was a calcium one or not, I was trying to remember whether it was the battery that was in the car when my dad bought it or not. The fact that I only put it on charge on a 4A charger for about 30 mins was enough to start the car made me think it was low on capacity.

I'll get my meter out tomorrow and check the output of my alternator though.

[kelvinp]

checked alternator output today and it was around 14.5v and didn't vary that much with all the lights and fan on.

I'll put it down the other battery being iffy as to why it wouldn't start, and the fact that after putting it on charge for just 1/2 hour it started straight away - couldn't find any other reason and I didn't do anything else other than check for a spark and put a can of fuel in just in case. It turns over much faster now as well.

I have a Halfords trade card so got a bit off the new battery.

[Laird Scooby]

Originally Posted by kelvinp

checked alternator output today and it was around 14.5v and didn't vary that much with all the lights and fan on.

I'll put it down the other battery being iffy as to why it wouldn't start, and the fact that after putting it on charge for just 1/2 hour it started straight away - couldn't find any other reason and I didn't do anything else other than check for a spark and put a can of fuel in just in case. It turns over much faster now as well.

I have a Halfords trade card so got a bit off the new battery.

I'd put it down to an alternator fault based on that!

If you don't have a smart alternator, it should be 14.4V on a cold regulator, dropping to 14.0V when it's warmed up. If you have a smart alternator, it should be about 0.7V higher on both (14.7 - 15.1V) - as such 14.5V is in "nomansland" and is either overcharging a normal lead-acid battery or undercharging a calcium battery.

Note that calcium batteries still use lead-acid but one set of plates is coated with a calcium compound and on normal lead-acid batteries, one set of plates is coated in Lead-antimony - both of these coatings promote the electrolytic action to make the battery work.

There are cheaper places to buy batteries than Halfrauds, even after their trade discount!

https://advancedbatterysupplies.co.uk/

You'll need either an 027 or an 096 (now often called a "100") for yours, depending whether it's petrol or diesel and the engine size. The 096/100 can be fitted to all models anyway to give more of a reserve.

[kelvinp]

I'll recheck with my DVM and I'm sure I have a voltage regulator somewhere.

I've already got the battery anyway, it was on 075 that was in it so that's what I've put back in it. It's a 2.0L petrol auto.

I'll see how it goes.