Alternators and Blocking Diodes

[xeitosaphil]

Having just finished electrical installations and checking charge voltages and current flows with regards to alternator charging and batteries, and checking to see if everything is working properly, I have come across an unforeseen situation.
The new Prestolite Alternator charges at 14.45v to 14.5v , having charged for 1/2hr with no load on the battery the voltage remains constant although the Amps reduce as they should.
Checked Batteries - to find bubbles just starting to form - (assume gassing starting)
Contacted supplier who told me they didn’t know charge output to be 14.4v ( nothing specified in their suppliers spec). It is apparent now that alternator suppliers are starting to increase their alternator outputs to 14.4v from original 13.8v, or so he says. Their only suggestion /solution for me to reduce output to 14.0v is to put a blocking charge Diode in line to cause a 0.5v drop in voltage thereby keeping it under gassing levels. They say that the alternator has a non adjustable / potted regulator.

Will a constant output from alternator at 14.5v be a problem regards gassing if left?

Is there any other way I can reduce Voltage to 14v to keep battery voltage to a level below gassing - I have only just fitted a new VSR and associated wiring so I am loathed to remove it all and start again.

If I have to put a Diode in to drop the voltage, could I put it in the alternator feed to the Engine battery and still keep the VSR for charging the Domestic bank?

 

[pvb]

Will a constant output from alternator at 14.5v be a problem regards gassing if left?

Is there any other way I can reduce Voltage to 14v to keep battery voltage to a level below gassing - I have only just fitted a new VSR and associated wiring so I am loathed to remove it all and start again.

If I have to put a Diode in to drop the voltage, could I put it in the alternator feed to the Engine battery and still keep the VSR for charging the Domestic bank?

Charging at 14.5v won't be a problem, unless you have gel or AGM batteries. You don't need to mess about adding diodes.

 

[oldbilbo]

"....Charging at 14.5v won't be a problem, unless you have gel or AGM batteries...."

So, with two new AGM batteries sitting here ready to be installed as No2, and considering keeping existing 110Ah sealed/wet battery as No1, what significant changes must I make....?

 

[Rigger Mortice]

So, with two new AGM batteries sitting here ready to be installed as No2, and considering keeping existing 110Ah sealed/wet battery as No1, what significant changes must I make....?

Mixing Batteries
The reasons we do not recommend wet cell and AGM Batteries together are:

1. When charging, the AGM will reach full charge before the wet cell. This means that the charge system will do one of two things. It will keep charging until the wet cell is fully charged and may over-charge the AGM or it will switch off when the AGM is fully charged which means the wet cell is only partially charged.

2. The wet cell will try to draw power from the AGM and this will reduce the life of both batteries because of under-charging then draining them will naturally damage both batteries but will kill the wet cell quickly.

If both batteries are charged separately, like in most dual battery set ups you can use the two together. With a voltage sensitive regulator or blockout diode (used in most dual battery systems) the start battery is charged first then it switches over to the 2nd or house battery.

The advantage of having 2 AGM batteries is that both can be used for starting or house use in an emergency and quicker charging means less drag on the alternator.

From http://www.firststartbatteries.com.au/faq.html

 

[NB Willawaw]

What sort of batteries are you using and what is the voltage measured at the battery terminals ?

 

[sailinglegend420]

1. Batteries need to get to the charging voltage at which they just start to gas to charge properly - this stirs up the electrolyte (EDITED FOR MORE CLARITY)
2. Batteries start gassing at 14.4 volts at 25C
3. Deep cycle batteries must have an external multi stage regulator on the alternator - especially AGMs or Gels
4. Set the charger to the battery manufacturers recommended voltages - AGMs and wets may have the same charging voltages so can be charged together
5. Charge the service battery first as it takes the longest - the starter battery will charge very quickly afterwards
6. Use temperature sensors on the battery and the alternator for a longer life for both

 

[Tranona]

Have 2 separate banks with a split charge system. Problem only arises if you mix the two in the same bank.

 

[xeitosaphil]

Charging at 14.5v won't be a problem, unless you have gel or AGM batteries. You don't need to mess about adding diodes.

The Batteries are wet cell type but my only concern was if left to continually gas the gas could build up, and with the gas being explosive and electrics in the same compartment wouldn’t it be an incident waiting to happen, or am I worrying unnecessarily.

I suppose I could always vent the locker if thought necessary?

 

[NB Willawaw]

open wet cells can easily take that charge voltage. The battteries will give off gas and the compartment should be vented.

 

[pvb]

The Batteries are wet cell type but my only concern was if left to continually gas the gas could build up, and with the gas being explosive and electrics in the same compartment wouldn’t it be an incident waiting to happen, or am I worrying unnecessarily.

I suppose I could always vent the locker if thought necessary?

A vented locker is a good idea. My batteries are in vented lockers under the aft cabin berths, with 1.5" pipes to mushroom vents on the outside of the cockpit coamings.

 

[xeitosaphil]

Nice clean, dry, vented, arrangement - mine is outside in the starboard cockpit locker (not airtight) - so may be able to just vent the top coaming for any massive build up.

So 14.5v is nothing to worry about, I thought 14.0v was the norm, as the Adverc cycles at that voltage 14.0v to 14.4v. ( under the gassing levels )

Is Sailinglegend correct when he says “ batteries need to gas to charge properly ”

 

[pvb]

So 14.5v is nothing to worry about, I thought 14.0v was the norm, as the Adverc cycles at that voltage 14.0v to 14.4v. ( under the gassing levels )

Most modern automotive alternators are regulated at around 14.5v, vehicle batteries are usually fairly fully charged, yet vehicle batteries last for years.

If you have an Adverc fitted, it's worth noting that it can only increase the voltage set by the alternator's integral regulator, it can't decrease it. (The same applies to the Sterling regulator).

 

[Plevier]

Is Sailinglegend correct when he says “ batteries need to gas to charge properly ”

That could be misread. I would say, batteries will gas at the voltage you need to reach to recharge fully.
Modern batteries particularly lead calcium will not gas very much at 14.5V. Old style high antimony ones will but you'll only encounter this alloy nowadays in specialist deep cycle batteries. "Leisure" ones all seem to be lead calcium now. Better for gas loss and shelf life, less good for cycle life and high temperature tolerance.
I'm quite surprised at 14.5V though, I thought about 14.2V was the norm for alternators now. However it's not going to do any harm unless you motor for days on end and presumably you avoid this by putting the raggy bits up now and then.

 

[xeitosaphil]

Most modern automotive alternators are regulated at around 14.5v, vehicle batteries are usually fairly fully charged, yet vehicle batteries last for years.

If you have an Adverc fitted, it's worth noting that it can only increase the voltage set by the alternator's integral regulator, it can't decrease it. (The same applies to the Sterling regulator).

What surprises me is the alternator is not a automotive one regulated at around 14.5v, but one purchased as an Adverc Package so really should be a 14.2v or less output to make the Adverc work efficiently. I realize the Adverc controller won't regulate voltage downwards as I was told this by the supplier, and only upwards when the output current from the alternator reduces the voltage due to a deeply discharged battery, but that is why it should charge at a lower level voltage to start with, as I see it?

I can see the point about automotive alternators are regulated at around 14.5v, as any gasses produced would only be lost by natural ventilation out of the bonnet maybe so not a problem as in Marine applications.

 

[pvb]

Contacted supplier who told me they didn’t know charge output to be 14.4v ( nothing specified in their suppliers spec). It is apparent now that alternator suppliers are starting to increase their alternator outputs to 14.4v from original 13.8v, or so he says. Their only suggestion /solution for me to reduce output to 14.0v is to put a blocking charge Diode in line to cause a 0.5v drop in voltage thereby keeping it under gassing levels. They say that the alternator has a non adjustable / potted regulator.

What surprises me is the alternator is not a automotive one regulated at around 14.5v, but one purchased as an Adverc Package so really should be a 14.2v or less output to make the Adverc work efficiently.

I'm surprised now. Adverc generally supply a 90A Prestolite 110-602 or 110-603 alternator. Both of these use the 8RG2043 regulator, which is adjustable. Perhaps you should look at the back of your alternator and see whether the regulator looks like the photo below. If so, the little white plastic recessed screw in the cutout section of the label at the lower end of the regulator is the adjustment method.

 

[xeitosaphil]

I'm surprised now. Adverc generally supply a 90A Prestolite 110-602 or 110-603 alternator. Both of these use the 8RG2043 regulator, which is adjustable. Perhaps you should look at the back of your alternator and see whether the regulator looks like the photo below. If so, the little white plastic recessed screw in the cutout section of the label at the lower end of the regulator is the adjustment method.

It's the same as one of these in the link- sorry can't find a suitable picture.

http://www.ebay.co.uk/itm/12v-90A-P...ssories_SM&hash=item33820f8396#ht_2165wt_1255

 

[pvb]

It's the same as one of these in the link- sorry can't find a suitable picture.

http://www.ebay.co.uk/itm/12v-90A-P...ssories_SM&hash=item33820f8396#ht_2165wt_1255

Well, if it's one of those, the regulator isn't adjustable. Would Adverc take it back and swap it for one with an adjustable regulator?

 

[xeitosaphil]

Well, if it's one of those, the regulator isn't adjustable. Would Adverc take it back and swap it for one with an adjustable regulator?

Not sure would have to ask them , but I would need to know if the footprint is the same as this one, to see if it will actually fit on the Yanmar2GM20 with no alterations?

Will check out the Prestolight Web site for the code numbers you have supplied and see if they are compatible size wise.

 

[Plevier]

You could keep the alternator and have a refund on the controller that isn't doing anything

 

[NB Willawaw]

The voltage will be fine. A little moderate gassing wont hurt, but check the electrolyte levels regularly.

Ive run open cells at higher voltages than that without a problem.

Nice clean, dry, vented, arrangement - mine is outside in the starboard cockpit locker (not airtight) - so may be able to just vent the top coaming for any massive build up.

So 14.5v is nothing to worry about, I thought 14.0v was the norm, as the Adverc cycles at that voltage 14.0v to 14.4v. ( under the gassing levels )

Is Sailinglegend correct when he says “ batteries need to gas to charge properly ”