Battery charging voltage

[pvb]

Brought to you, perhaps, by the same people who suggest that the charge should first go to the start bank (which is almost never depleted) rather than to the house bank.

In the context of a VSR (or a "combiner" or "ACR" in US-speak), it surely makes good sense to ensure that the start battery gets priority?

 

[BabaYaga]

Machine sensed

Beta alternators are battery sensing through a small brown wire conncted to the ignition switch. The alternator regulator will "see" the voltage in the engine battery and react accordingly. When you have both banks in parallel it will see the resultant combined voltage.

The standard 40 A alternators are, but I believe the OP's optional 70 A alternator is machine sensed. At least that is the case on my Beta 722 from 2006. Alternator made by Iskra.

 

[Chris_Robb]

I think many people would disagree with that. Regardless, the OP is talking about a normal alternator voltage, and it's too high.

I would not agree with you if this was an alternator controller, which has a 3 stage charge (14.4 for sealed LA) including float at 14.2max. What is his alternator going to do when it should be floating - still charge at 14.8 because there is no clever electronics??? His batteries will fry in no time at all.

The bit about setting the Solid state switch is an irrelevance to this conversation - its about an alternator producing the wrong output. It should be no more than 14.2 for LA and less for Gel.

 

[VicS]

I agree the alternator output volts is too high!

However i am not convinced that is the cause of the non charging of the house bank
The specs for the Blue Sea ACR seem to say that the high voltage lockout is set to 16 volts. That does seem more reasonable than some figure below 14.8.

They also mention something about a "Start isolation" feature". Is that something which has not been reconnected during the engine change or connected incorrectly?

Troubleshooting page HERE

Returning to the 14.8 volt issue

What if the alternator is a battery sensed one and the sense wire has not been connected or has been connected to the wrong battery. What will its output be. None, a safe maximum such as 14.8, or something way above that?

 

[Stu Jackson]

In the context of a VSR (or a "combiner" or "ACR" in US-speak), it surely makes good sense to ensure that the start battery gets priority?

pvb - We just seem to have different opinions. You folks believe the start battery requires an immediate charge and all charging should go to it first. We differ in that we feel the house bank, which may be discharged way more than the start bank, should take priority. One uses perhaps a few amp hours to start a small diesel engine such as the ones most of us have. You could start your engine10 to 15 times on a small start bank without getting anywhere near the 50% depletion of the battery. OTOH, house banks can get depleted say overnight at anchor, or just on a daysail. We simply charge the house bank first from the alternator, then through a combiner, echo charger, duo charger, etc. or a simple switch.

It is simply the difference between using the start bank as a reserve, and using and running everything, including engine starts, from the house bank.

You can read more about it in prior posts, say do a search on 1-2-B switch, and material that I've contributed and from Maine Sail.

We fully understand your point of view, have different opinions, and let's leave it at that. Works for us.

That's all. I don't mean to start this discussion all over again, just don't know if you've read it before, so I offer this particular example of the reasoning.

Here's one of Maine Sail's explanations of the issue:

The start battery is almost always at 98-99% charged anyway. Feeding it first is not necessary and can only serve to limit the house bank depending upon your ACR.

Starting the engine requires very, very little from a battery, many folks over think this and believe it requires a lot more than it really does. The peak in-rush current draw for a split second on my 44HP four cylinder Westerbeke is about 160 amps. My 44hp four cyl diesel engine does not even consume .1 ah from a 240 ah bank for starting! The starter motor on my Westerbeke is a 1.5 kW an the starters on the M-25's are .8 kW.

Any deep cycle bank will have way more than is needed in MCA's to crank a small diesel aux. For over 20 years I have started my engines off my house banks including a very large Cummins diesel in Downeast cruiser.

Battery acceptance and state of charge are the real questions. We must ascertain just what or why boaters thed to believe they would be limiting the recharging ability of the engine battery by first routing to the house bank and not the start.

As I mentioned above small diesel engines really don't take much battery capacity to start. In the context of battery acceptance you would really need to discharge a start battery considerably before it could even accept a charge.

We also need to keep in mind that the minute that ACR makes, the current from the full battery (your start battery in this case) starts dumping its charge and what the alt is putting out, into or through the ACR, and into the low bank along with what the alt can put in until max acceptance is met. This is one reason I prefer a Duo Charge or an Echo Charger because the full bank can't be bled off or cause a relay to make/break, make break.. With wet cells this is not a huge deal because of "acceptance" but with AGM's you can see a HUGE and FAST transfer of current between banks.

With an ACR type relay it does not matter as much where the alt is connected except that if you feed the reserve batt and it combines with a much bigger deeply discharged house bank it can cause a drop in voltage that can make the relay cut in and out many times before the house voltage can be sustained without cutting out the relay on low voltage. Feeding the hosue bank first avoids this game of cut in/cut out, cut in/cut out..

A fully charged start battery might wind up at 95-98% of capacity, after a worst case scenario start up, that perhaps involved more cranking than normal. This, to an alternator, is basically seen as a fully charged battery and it will react accordingly with low output limited by acceptance.

I have actually pulled my stop lever, closed my seacock and cranked enough, intermittently of course, to have water-locked my engine if I had left the seacock open. I still used only about 1% of the 240 ah banks capacity leaving me at a 99% state of charge. Even one full minute of cranking with a 150 amp starter draw is still only 2.5 amp hours from a battery.

On even the smallest group 24 start battery, with roughly 65 amp hours available, this still leaves you at over a 96% state of charge. Considering the acceptance rates of wet cell batteries is roughly 20-25% of the 20 hour rating the MAX a 65 ah group 24 wet cell will accept, when it is flat out dead, is about 16 amps. The 16 amps only happens of course when the battery is basically dead. At 96% SOC you'll be lucky to force even one or two amps into it. Even if you were to consume 5% of the ah capacity your battery will still barely be accepting 1-2 amps at the most depending upon the start bank size and chemistry. AGM's of course accept a lot more than wet cells do.

By wiring to the start battery first, and sensing it, you can actually cheat your whole system of alternator output. This is why Xantrex designed the Echo Charge. They recognized that the start battery will rarely if ever need more than about 15 amps in reality will usually only need an amp or two. Their directions are clear that you should wire to the house bank first and then use the Echo to feed a start battery or other aux battery.

One reason I really like the Balmar Duo Charge is because a start battery generally does not need the 14.2-14.4 volts the house bank does, as it resides almost 100% of the time above 95% SOC, or what we refer to as float voltage range. When a start battery is sitting at 98-99% SOC a device that can send 13.2-13.4 to the emergency/start batt and 14+ to the house bank, is a smart device indeed. ACR's and the Echo Charger don't do this but the Duo does. ACR's and the Echo are voltage followers. Combiners combine and thus the bank becomes one homogenous voltage thus over charging is not possible unless you have a single stage regulator with a high set point and constant 14.6 volts out.

There is nothing wrong with an ACR, they work well, but I agree 100% with Stu in that your alt and charging system would be better served by wiring the alt directly to the house bank first, not the start battery first.

 

[William_H]

Battery charging

The suggestion that there should be a small brown wire to sense the voltage is worth investigation. The wire should be found first at the alternator regulator (attached I imagine to the alternator end opposite the pulley. If this wire can be traced that may help. It should go to IMHO the engine battery after the "ignition" switch. (engine power )
if it has been connected to the house battery then the house battery will show a lowish voltage making the alternator produce more volts. but this high voltage has caused a disconnect at the VSR. So you would continue to get high charge voltage.
Now this could all be checked by operating the emergency parallel switch used for starting the engine off the house battery or if that is not successful or possible then connect the +ve of the engine battery and start battery together. This will make the sense come from both batteries both being charged. The voltage should go down to more normal 14v or less. If this does fix the problem then possibly the alternator sense wire is connected to the house battery.
Beware however that the batteries not being fully charged will pull the voltage down anyway so check the voltage after some time of running.

Just in case you are confused by this sense wire. An alternator needs a current about 1 amp max to pass through the field coils. These are the rotating coils fed via the brushes. More field current means more alternator voltage. A little electronic circuit varies this current by comparing the output voltage of the alternator to a voltage reference (a fixed voltage produce d by a zener diode.) The voltage from the alternator is most often simply sampled from the output terminal of the alternator. However it has been suggested that this voltage is sampled via a small brown wire which can be connected to the battery +ve. Normally of course battery positive is connected to the alternator output so same thing. However if diodes are used for isolation (instead of VSR) then the sample used to determine alternator output voltage is taken from the battery voltage as sensing the end result rather than alt output.

I hope this helps good luck olewill

 

[pvb]

What if the alternator is a battery sensed one and the sense wire has not been connected or has been connected to the wrong battery. What will its output be. None, a safe maximum such as 14.8, or something way above that?

The alternator voltage would increase. However, if the voltage at the battery terminals has been measured as 14.82v, the VSR should connect the batteries. As we've both pointed out, the overvoltage disconnect should be in the region of 16v, so shouldn't be operating.

 

[Chris_Robb]

I agree the alternator output volts is too high!

However i am not convinced that is the cause of the non charging of the house bank
The specs for the Blue Sea ACR seem to say that the high voltage lockout is set to 16 volts. That does seem more reasonable than some figure below 14.8.

They also mention something about a "Start isolation" feature". Is that something which has not been reconnected during the engine change or connected incorrectly?

Troubleshooting page HERE

Returning to the 14.8 volt issue

What if the alternator is a battery sensed one and the sense wire has not been connected or has been connected to the wrong battery. What will its output be. None, a safe maximum such as 14.8, or something way above that?

The start Isolation wire should ensure that the batteries are disconnected during starter operation. I believe that is a safety feature just in case one battery bank is very flat resulting in massive amps flowing across the VCR. If this is wired incorrectly could it actually be isolating the batteries, thinking it is in start mode??

 

[VicS]

The start Isolation wire should ensure that the batteries are disconnected during starter operation. I believe that is a safety feature just in case one battery bank is very flat resulting in massive amps flowing across the VCR. If this is wired incorrectly could it actually be isolating the batteries, thinking it is in start mode??

The start isolation is a feature that prevents the house bank being connected while the starter is being used ( But you'd think the normal operation of a VSR / ACR would rule that out anyway ) So that sensitive electronics are not upset.... at least that what I understand from reading the description.

Following the diagnostic chart in my link one can end up at the box that suggests that the start isolation wire may have been connected to a 12volt source which is energised even when the starter is not being used. ... It should be connected ( if at all) to a point that is only energised when the starter is used.

Probably not the trouble, although it could be and therefore it is one aspect of the installation to check.