Alternators and charging

[bottle]

Slightly

 

I have an MG roadster in my garage that has not moved or been started for over 12 months. I went to it yesterday, expecting totaly flat batteries (2*6volt), and she wound up and started first time.

 

Also the batteries have not been touched or charged in that time.

[jollyroger]

Why not spend about £300 and buy a generator?

[Amicus]

http://www.airflow-uk.com/battery-conditioner.htm

 

No comment

[John Orentas]

Looks like a pretty useless bit of kit, seems it is designed to keep a fully charged battery, charged. Does not even specify the charge rate and measuring the voltage with a zero load is not the best idea in the world.

But then what do you expect for 30 odd quid.

[Big COL]

Looks like a pretty useless bit of kit, seems it is designed to keep a fully charged battery, charged.  Does not even specify the charge rate and measuring the voltage with a zero load is not the best idea in the world.

But then what do you expect for 30 odd quid.

<{POST_SNAPBACK}>

 

 

Hi John

 

To which are you referring when you say (looks like a useless bit of kit ) If you google for optimate all the technical information is on there. My biker friends all use this charger connected permanently on their classic bikes and cars. The optimate is certainly NOT a useless bit of kit, and as I have already stated they make a model that is capable of maintaining a 110 amp hour stater battery and it has served me very well connected to my thruster battery and prior to that it was connected to my 4/4 Morgan which was garaged through the winter and would always start first time when asked.

Now you have got me tearful as this has reminded me that I had to sell my one true love to help fund the new boat, but in my opinion it is a super piece of equipment connect it and forget it.

[John Orentas]

Hi Colin.

 

I think we are talking about very different things. If you simply want to keep car or bike battery topped up over the winter then a one amp trickle charger is all you need. The original requirement here was for the re-charge of a 110ah or larger bow thruster battery.

[Big COL]

Hi Colin.

 

I think we are talking about very different things. If you simply want to keep car or bike battery topped up over the winter then a one amp trickle charger is all you need.  The original requirement here was for the re-charge of a 110ah or larger bow thruster battery.

<{POST_SNAPBACK}>

 

John

 

The model I use does that.

[Richard Bustens]

Well over the w/end i sorted out the problem with the bow thruster getting weaker as the journey went on the boatyard had not connected the cables from the main batteries in the engine room to the bow thruster ones in the bow.

 

Now two points bother me, with the cabling between the two being only 16mm i have not connected the two together yet , will the surge of current going from the fully charged main batteries to the flat thruster ones cause a problem with these thin wires, and the same when the thruster is running it will obviously try to get extra from the main batteries, will the wires hold up,

 

I also suspect i should fuse these cables at both ends/

 

also when i connected the wires to the bow thruster batteries the neg is connected to the main but the pos is not, so there is no connection between the two sets, i put the neg on first and then whilst connecting the pos i had my arm leaning on the hull and when i touched the pos i got a tingle on my arm, a mild shock, that was continuous whilst holding the hull with one hand and the pos terminal with other, now i have never had a shock from 24v before and don't get this if i hold one terminal with one hand and the other with other hand, what could be causing this?

[Amicus]

Can you put a meter in place of your person, measure the voltage?

[Richard Bustens]

Did not think of that but it should read 24v ish

[Amicus]

Did not think of that but it should read 24v ish

<{POST_SNAPBACK}>

Should do.....

might be 36V?

[Richard Bustens]

Should do.....

might be 36V? 

<{POST_SNAPBACK}>

 

MMMuuu could be or 48 is more probabal but can't see how there is 24v at the main batteries and there is 24v at the bow thruster, i have conected the neg to neg together and the pos terminal onto the bow thruster but left it free and insulated at the other end so even if i had conected it to the wrong terminal it should not do that.If i have cross wired the neg from the bow thruster to the pos on the main batteries then tuched the earth on the hull and the pos terminal on the bow thrusters i would have got 48v i think ..

Edited May 16, 2005 by Richard Bustens

[John Orentas]

Richard.

 

In certain conditions you can detect a very low voltage, especially in slightly humid conditions and with a large conductive area onto your skin, (they knew that when they built electric chairs).

 

As for your 16mm cable, a line fuse at each end would not do any harm, I would rate it though at 150 amps or so. Don't worry too much about exploding cables and things, to take an extreme example you could probably put a direct short across a battery with a 100 ft length of 16mm cable it probably wouldn't even start to get warm for 20 seconds or so.

[Richard Bustens]

it was hot and dry yesterday but the feeling was on my wrist and under arm not on the hand fingers or the other hand. and i spose that is a sensitive area.

[John Orentas]

As the old joke goes Richard, don't get a job on the buses.

[onionbargee]

thanks for the thought.  I think you are assuming I will have a separate battery for the thruster. 

 

Actually I've done my sums and have decided to follow John O's recommendation to run seriously thick cables (70mm2) to carry 600A from the engine battery to the bow. 

 

I'm not intending to have a multi-inverter. 

 

Principle is K.I.S.S.

14945[/snapback]

 

That cables going to cost you, as i'm as tight as a nuns knickers, i would use a straight run of solid copper bar, which is a few quid for 4m lenghs, and some pvc conduit, that cable will never move in its life, so why pay for flexable cable ?

 

OH, on BSC inspections, just hide it !

[ChrisPy]

That cables going to cost you, as i'm as tight as a nuns knickers, i would use a straight run of solid copper bar, which is a few quid for 4m lenghs, and some pvc conduit, that cable will never move in its life, so why pay for flexable cable ?

 

OH, on BSC inspections, just hide it !

24432[/snapback]

£99 is not exactly a lot to pay to avoid all the problems of second batteries, chargers, etc..

 

By the way, nunion, you'll fall foul of the regs if you use a rigid conductor !!

[ShaneK]

Alternators are very likely to have a built in regulator that limits the available current and voltage. In order to charge the battery, a voltage in excess of the battery voltage must be applied. The current into the battery is defined by the difference in voltages, and the resistance in the circuit, including the internal resistance of the battery. Systems with a 12V battery are often referred to as 14V systems, and 24V -> 28V systems, because the 14/28V is what the alternator can output. However, this is only achieved when the battery is fully charged. If you want to limit the charge into the battery ... what is the point in such a big alternator. If you want the alternator to be able to provide power for appliances, fair enough, but be aware of the output voltage that may be produced.

 

If you want to reduce the charging current, the simplest way is to put a couple of diodes in series with the battery. These will drop about 0.7v each. Discharge current also through a diode, but this will need to be a much bigger one .. to pass heavy load current. This could be part of a "splitter", or both parts in parallel.

 

There is also the matter of load dump !. This is a high voltage produced when a heavy load is disconnected, and can exeed 80V. Just be aware of it.

 

Shane

[bottle]

Shane

 

Welcome to the forum

 

 

No doubt the info you give is correct but

 

 

Congratulations on resurrecting a thread that is over three years old.

[chris w]

Alternators are very likely to have a built in regulator that limits the available current and voltage. In order to charge the battery, a voltage in excess of the battery voltage must be applied. The current into the battery is defined by the difference in voltages, and the resistance in the circuit, including the internal resistance of the battery. Systems with a 12V battery are often referred to as 14V systems, and 24V -> 28V systems, because the 14/28V is what the alternator can output. However, this is only achieved when the battery is fully charged. If you want to limit the charge into the battery ... what is the point in such a big alternator. If you want the alternator to be able to provide power for appliances, fair enough, but be aware of the output voltage that may be produced.

 

If you want to reduce the charging current, the simplest way is to put a couple of diodes in series with the battery. These will drop about 0.7v each. Discharge current also through a diode, but this will need to be a much bigger one .. to pass heavy load current. This could be part of a "splitter", or both parts in parallel.

 

There is also the matter of load dump !. This is a high voltage produced when a heavy load is disconnected, and can exeed 80V. Just be aware of it.

 

Shane

 

The aproximate 14v voltage, at the output of the alternator, is achieved way before the batteries are fully charged. The batteries need a prolonged spell (many hours) at this maximum voltage to achieve full charge. The current at this stage will be self-limiting as the battery terminal voltage rises. Actual regulator voltage is typically around 14.2v as standard but can be raised by using an external regulator (alternator controller) which will raise the 14.2v up to 14.8v which is a much better charging voltage for wet lead acid batteries. Gel batteries should not be charged above 14.4v. (Alternator controllers are usually switchable for different battery types).

 

The built-in regulator controls the voltage at the output of the alternator (if machine sensed) or the voltage at the battery (if battery sensed). Alternator controllers have the added advantage of being battery sensed. The regulator does not limit the maximum curent at all. The maximum current is determined by the resistance of the stator windings.

 

Chris

[chris w]

Don't worry too much about exploding cables and things, to take an extreme example you could probably put a direct short across a battery with a 100 ft length of 16mm cable it probably wouldn't even start to get warm for 20 seconds or so.

 

I had an interesting read through this thread as it predated my joining the Forum.

 

If anyone reads JO's statement above (due to this thread's being resurrected) DO NOT rely on the comment that JO made.

 

Run the maths.............. 30 metres of 16mm² cable will have a resistance of 32 milliohms (.032 ohms). The current that would flow, if one did short this cable out, would be almost 400 amps and the power dissispated in the cable would be over 4.5 KILOWATTS. A fire is a distinct possibility.

 

Not only would the cable instantly get red hot but the battery may explode spraying hot acid all over the place.

 

Be warned!!

 

Chris

[Guest]

I had an interesting read through this thread as it predated my joining the Forum.

 

If anyone reads JO's statement above (due to this thread's being resurrected) DO NOT rely on the comment that JO made.

 

Run the maths.............. 30 metres of 16mm² cable will have a resistance of 32 milliohms (.032 ohms). The current that would flow, if one did short this cable out, would be almost 400 amps and the power dissispated in the cable would be over 4.5 KILOWATTS. A fire is a distinct possibility.

 

Not only would the cable instantly get red hot but the battery may explode spraying hot acid all over the place.

 

Be warned!!

 

Chris

Happy days

[John Orentas]

I had an interesting read through this thread as it predated my joining the Forum.

Be warned!!

 

Chris

 

 

 

Been out for most of the day.. Has this bloke really dug out a 3 year old thread as is picking an argument over it.

 

PATHETIC

[bottle]

No he did not dig it out, someone else did.

 

Looks like another 'electrikery expert'.

[Guest]

No he did not dig it out, someone else did.

 

Looks like another 'electrikery expert'.

How many can one forum contain?