Battery Or Other Electrical Gremlin

[Guest mcramsay]

I've had a pc680 gel pack battery to power my kit, it's been in the car two years, and to be fair the car has never been driven, and the battery has sat for months on end without being charged.

I made a post a few months ago that when running my engine at idle the battery voltage was less than 12v, when I brought the revs up a bit they would rise to around 13.5-14 volts. Eventually if I left the car idling after around 15 mins it would cut out due to the falling voltage.

 

Now with all my electrics wired up and working I fully charged the battery for a day and the voltage was 12.4v which I thought was a little low for a fresh battery, as soon as I turn on any electrics on the car the voltage drops to 11.5 volts. I'm guessing a fresh battery shouldn't drop like this when its fully charged? When it's basically dash LEDs and the ecu electrics?(engine not running)

 

Or could something else electrical cause this voltage drop?

 

I'm still struggling to work out if this all adds up with the alternator issue, either I've not got it spinning fast enough to give a proper out put. It's only a 40a alternator, In not sure if I can raise the idle with the throttle cable, as the ecu has an iacv which controls the idle as per the ecu setting and I would end up moving the tps off the Idle setting on the map fuel map

[Guest mcramsay]

Whoops wrong forum, if any mods are around this was meant to be in the electrical section

[Guest mcramsay]

I have always disconnected the battery, never leave it connected. The alt is also new, but it is a cheap Nippon copy so there is a chance it's nackered, I will do some testing when the engine is running and see what amps it's putting out at idle, and what effect raising the idle has. Also what it's doing when the car is fully loaded up.

 

I think there are some chargers designed to recover gel pack batteries and charge them, I will look into it.

 

Sadly there is only room for a small gel pack battery no other battery will fit

[IanS]

Could be a bad earth to the alternator.

A quick check is a jump lead from the alternator body to the battery -ve and then check the battery volts.

[Guest mcramsay]

I was just looking over the car, the engine has a nice sized earth to the chassis, my main earth from the battery runs to a m6 bolt on the engine.... I think that might be the problem. I think I run the earth as a temp solution as I did not have the proper cable, and looks like I completely forgot about it. I'm guessing if the main earth to the battery is too small then you would get a Restriction?

 

What size cable have people used for ground wires? And should you ground the battery negative to both the engine and chassis?

[IanS]

I use the same size as for the power to the starter. I do not remember the exact size but around 8mm diameter probably 50mm2

I run seperate cables battery to engine and battery to chasies.

[Guest mcramsay]

I'm surprised the car started like that, I am even more surprised and annoyed that I overlooked it. I'm going to upgrade the earth cable to the same as the starter cable size, and earth from the battery to the chassis and the engine. Not saying it will cure my problems but what i have done is wrong.

 

The main earth from my batt to engine is only half the size of the starter.

 

Must remember to make lists and not forget things

[fry61]

25mm cable should be more than adequate it has more than 100amp continuous rating -- connections are more likely the weak spot -- ensure all are clean & tight. The gel batteries generally only have an M6 stud or tapping.

Edited January 10, 2016 by florin metal works

[Guest 2b cruising]

As Bob says above.

If this proves unsuccessful and you feel the need for turning the alternator a little faster, fit a smaller drive pulley to it.

[Guest mcramsay]

Sadly I can't find any smaller drive pulleys, and since moving off the tools no longer have access to a lathe at work, does any one on here fancy turning me up a new 5 groove pulley?!

[Guest Jasony939]

Hi, I could be wrong but I'm sure alternators charge about 13.5v at idle. So it sounds like an alternator fault. If it's idling and not charging the battery will go flat quite quick if powering modernish ecu etc.

The battery might also be faulty but I would address the alternator first.

For charging them my father always says "slow charge" as it says slow and fast in the charger. Really the transformer in the charger has 2 outputs, one about 11.5 and the other at 12.5v approx so that's what it's doing.

Hipe you get it sorted.

[fry61]

Sadly I can't find any smaller drive pulleys, and since moving off the tools no longer have access to a lathe at work, does any one on here fancy turning me up a new 5 groove pulley?!

 

Size of present pulley is ??? May have a smaller one in stock Craig.

[Guest mcramsay]

The pulley size at the moment is 54mm, which gives an rpm or around 1800 alternator rpm at idle, been looking at a few graphs and they don't seem to start generating more than ten amps until over 2000 rpm. So I'm looking to change to a 47mm pulley looked all night on eBay and finally found one. Will still need a bit machining to fit though. I don't know what the issue is. Combination of a large crank pully diameter and an alternator that is only rated for 40A. Might be a bit on the small side... Need to do more investigation when I can run the engine. It definatley charges if you raise the Rpms just a little.

[fry61]

The large crank pulley diameter can only help the alternator RPM --- 100mm crank pulley to 50mm alt pulley = 2 to 1 so alternator RPM will = 2 times crank RPM. which is born out by your post above.

[Guest mcramsay]

Whoops got that backwards! Thanks for the correction. Anyway it's something I have to park for now and test when I can run the engine again. Should be easy enough to sort rather than guess what's wrong at this stage.