Alternator voltage

[dor]

I've replaced the regulator in my Iskra alternator with a Cargo one regulated to about 14.5V (original one 14.0V).  It started out OK but now only regulated to 13.85 to 14.2 volts. I've swapped the regulator for a known good one with the same result so now I suspect the alternator.  In my experience, faulty alternators are usually down to the diodes and output either next-to-nothing or about 11V.  Is there an alternator fault that would reduce the output by about half a volt?

All expert opinions welcomed.

[tommytelford]

I would have thought that was about right if the battery is fully charged, or thereabouts

 

[Alan de Enfield]

10 minutes ago, dor said:

All expert opinions welcomed.

EXPERT :

An Ex is a 'has-been' and a spurt is a 'drip under pressure', so with that in mind I'd suggest :

 

Use a 15v regulator and achieve 14.5v

[dor]

1 minute ago, tommytelford said:

I would have thought that was about right if the battery is fully charged, or thereabouts

 

Maximun voltage is the same regardless of state of charge.

2 minutes ago, Alan de Enfield said:

EXPERT :

An Ex is a 'has-been' and a spurt is a 'drip under pressure', so with that in mind I'd suggest :

i

Very often the case, especially on here!   However there are some members whose opinion I would happily listen to.

[WotEver]

14 minutes ago, dor said:

Maximun voltage is the same regardless of state of charge.

Very often the case, especially on here!   However there are some members whose opinion I would happily listen to.

You need @Tony Brooks or @Sir Nibble for the true words. 

 

I presume you're measuring the voltage at the back of the alternator and not at the batteries? 

[dor]

1 minute ago, WotEver said:

You need @Tony Brooks or @Sir Nibble for the true words. 

 

I presume you're measuring the voltage at the back of the alternator and not at the batteries? 

Yes.

 

Have now swapped alternators for another 'identical' Iskra with the same type of regulator and getting 14.5V as expected.

[Nickhlx]

My Iskra 175 has its output voltage set at 14.8 volts, and the bank of Trojans it empowers is now 10 years old.  

 

The meter being used might be slightly pessimistic so you may be actually getting a slightly higher voltage...

[Tony Brooks]

3 hours ago, dor said:

Maximun voltage is the same regardless of state of charge.

Very often the case, especially on here!   However there are some members whose opinion I would happily listen to.

Absolute maximum voltage eventually yes, that is actually the regulated voltage but as charging current rises the charging voltage falls so the maximum achievable charging voltage at any given time is dependant upon the state of charge OR the load on the system. Flatter batteries and higher loads will give a lower maximum achievable charging voltage than that with well charged batteries or  lower loads.

 

This is why we have such difficulty when posters only quote voltages and no  currents. With just volatge it is impossb;le to differnetiate betaeen a faulty alternator or a good alternator delivering a high charging current.

 

I will add Wotever to the list.

 

 

[dor]

1 hour ago, Tony Brooks said:

Absolute maximum voltage eventually yes, that is actually the regulated voltage but as charging current rises the charging voltage falls so the maximum achievable charging voltage at any given time is dependant upon the state of charge OR the load on the system. Flatter batteries and higher loads will give a lower maximum achievable charging voltage than that with well charged batteries or  lower loads.

 

This is why we have such difficulty when posters only quote voltages and no  currents. With just volatge it is impossb;le to differnetiate betaeen a faulty alternator or a good alternator delivering a high charging current.

 

I will add Wotever to the list.

 

 

Currents are just what you would expect from a 95A alternator.   With batteries at about 60% SOC it starts at about 85A dropping fairly rapidly to about 60A, then a bit slower to about 35A. Voltage at this point is as high as it gets, as detailed above.  Current then gradually reduces at the batteries charge, often stopping at about 11A for a while.  Will eventually drop to under 4A, going into 5 x 110A SLA batteries.  This is just what I would expect,  I'm just concerned why the charging voltage is about 0.5V lower than I would expect, and after changing the alternator for another 95A identical alternator with the same regulator, I get the expected 14.5-14.6 or so volts charging current I would expect. Currents fall in much the same way.  Both alternators will eventually get to the same point, but I would expect the higher regulated voltage to allow it to get there quicker.  After all, that is the whole point of upgrading the regulator, either internally or externally. 

Incidently, I have a Sterling PDAR "advanced" regulator which I have disconnected.  It would charge at 14.8V, but drop into float (13.8V) after one hour, regardless of the state of charge of the batteries, despite it claimed that it calculates how long to maintain the boost voltage and will continue the boost for anything up to six hours.

[Neil Smith]

I have a sterling alternator to battery charger and it charges at 14.8v until batteries are fully charged only then going to float.

Neil

[cereal tiller]

5 minutes ago, Neil Smith said:

I have a sterling alternator to battery charger and it charges at 14.8v until batteries are fully charged only then going to float.

Neil

IIRC the Stirling devices commence a one Hour period at 14.8 once 14 Volts is achieved.

[WotEver]

8 hours ago, Neil Smith said:

I have a sterling alternator to battery charger and it charges at 14.8v until batteries are fully charged only then going to float.

Neil

How are you determining this? Tail current, relative density? Or are you going on what the Sterling Box is telling you?

[Tony Brooks]

9 hours ago, dor said:

Currents are just what you would expect from a 95A alternator.   With batteries at about 60% SOC it starts at about 85A dropping fairly rapidly to about 60A, then a bit slower to about 35A. Voltage at this point is as high as it gets, as detailed above.  Current then gradually reduces at the batteries charge, often stopping at about 11A for a while.  Will eventually drop to under 4A, going into 5 x 110A SLA batteries.  This is just what I would expect,  I'm just concerned why the charging voltage is about 0.5V lower than I would expect, and after changing the alternator for another 95A identical alternator with the same regulator, I get the expected 14.5-14.6 or so volts charging current I would expect. Currents fall in much the same way.  Both alternators will eventually get to the same point, but I would expect the higher regulated voltage to allow it to get there quicker.  After all, that is the whole point of upgrading the regulator, either internally or externally. 

Incidently, I have a Sterling PDAR "advanced" regulator which I have disconnected.  It would charge at 14.8V, but drop into float (13.8V) after one hour, regardless of the state of charge of the batteries, despite it claimed that it calculates how long to maintain the boost voltage and will continue the boost for anything up to six hours.

 

But for a very significant part of the charging period the regulator is doing nothing because  the highish charging currents are causing the charging coils inside the alternator to reduce the voltage so you do not get your stated regulated voltage. Lucas say that you can not check (therefore they do not expect you to reach) regulated voltage with more than 10 amps flowing (See Lucas test cards). Your higher regulated voltage probably only accounts for a number of minutes faster charge right at the end of charging. If you want a faster charge AND THE BATTERIES WILL ACCEPT IT then you need a higher output (current) alternator, not a higher  voltage regulator.

 

A higher volatile regulator will probably get the last 10% of charge into the batteries faster but if we take that Lucas 10 amp figure as reasonable then with a large bank of batteries or a  smaller bank of old batteries the tail current may be so high you never reach that point.

 

As Nicknorman points out the way the regulator starts to cut in seems rather "soft" (his word) so there will be a long period while i may be working but not at its stated voltage.

[Sir Nibble]

This is one of those damned awkward problems where before you decide what's wrong, you have to define "wrong".

I have met many regulators working below the voltage written on the box but you seem to have eliminated that. First thought is to take a voltage reading at the alternator D+ terminal in order to determine what the regulator is actually seeing.

[WotEver]

1 minute ago, Sir Nibble said:

I have met many regulators...

Did they work for OfAlt?

[Neil Smith]

3 hours ago, WotEver said:

How are you determining this? Tail current, relative density? Or are you going on what the Sterling Box is telling you?

I am going by my smart gauge, but unlike mike I only have one so cant check it against the other two.

 

Neil

[Tony Brooks]

52 minutes ago, Neil Smith said:

I am going by my smart gauge, but unlike mike I only have one so cant check it against the other two.

 

Neil

Well, as has been said so many times on here using it to tell you when you batteries are fully charged is subject to an error acknowledged by the designer so your batteries may not be fully charged.

 

Unless you have had to put a load of data into your Sterling device I would contend there is no way it can know when the batteries are fully charged any more than mains chargers (and probably solar) can. They all seem very keen to go into float too early. In fact I suspect they all tend to use the same "brain" chips and very similar algorithms.

 

As long as you check the Smarguage reads close to 100% after charging has stopped and some discharging has taken place its probably the best you can do to asses fully charged until you fit an ammeter or use a hydrometer. Smartguages are at their best when advising you to stop discharging and start charging PDQ as long as you realise daily charging is needed to maximise battery life.

Edited July 18, 2018 by Tony Brooks

[WotEver]

^^^^ this 

[Neil Smith]

3 hours ago, Tony Brooks said:

Well, as has been said so many times on here using it to tell you when you batteries are fully charged is subject to an error acknowledged by the designer so your batteries may not be fully charged.

 

Unless you have had to put a load of data into your Sterling device I would contend there is no way it can know when the batteries are fully charged any more than mains chargers (and probably solar) can. They all seem very keen to go into float too early. In fact I suspect they all tend to use the same "brain" chips and very similar algorithms.

 

As long as you check the Smarguage reads close to 100% after charging has stopped and some discharging has taken place its probably the best you can do to asses fully charged until you fit an ammeter or use a hydrometer. Smartguages are at their best when advising you to stop discharging and start charging PDQ as long as you realise daily charging is needed to maximise battery life.

thanks Tony,

I have got a BM1 so I can see amps going in and amps going out.

 

Neil

[Tony Brooks]

1 hour ago, Neil Smith said:

thanks Tony,

I have got a BM1 so I can see amps going in and amps going out.

 

Neil

Good, then you have the best combination possible.

 

Keep on charging at 14 volts or more until the charging current falls to around 1 to 2% of battery capacity. That is about as close to fully charged as you can get but note the 14V+ part. If your Sterling thing decides its going into float  you will have less than 14V and in this 0.1V can make a big difference. 

 

The other way to gauge fully charged is to keep monitoring the charging current and when if fails to fall over an hour or so its time to stop but note that the current will drop noticeably when the Sterling thing goes into float. Don't be fooled. Keep going at the new voltage until it stops dropping.

 

Start charging ASAP if the battery voltage drops to about 12.2 volts OFF LOAD or the Smartguage says 50% - but try to recharge every day. This 50% thing is to minimise loss of cycles and thus optimise battery life.

 

Once you are as sure as you can be that the batteries are fully charged and you stop charging zero the Ah out reading on the BVM. (If you have solar you may need cover it.) Next morning read the AH out and what the Smartguage tells you (or use the rested battery voltage to assess state of charge). So from the Ah out and the % discharged/charged reading you can calculate the actual battery capacity. So lets say the Ah out was 50 and the state of charge was 75%. that means 50Ah is 1/4 of the battery capacity so the full capacity is 200 Ah. Now you can enter that into the BVM setup and al;so alter the tail current to (say) 1%. Now for a few days/weeks any BVM reading related to battery state of charge will tell far smaller lies than it did before.

 

 

[Neil Smith]

Thanks Tony,

Next time I go to the boat I will do as you say.

 

Neil