Voltage Sensitive Relay theory

So does equalisation only happen over a gradual length of time? I thought it was instant??? ie, if you connect 2 batts together both at different voltages then they will equalise straightaway.

Can VSRs handle different types of batteries, ie conventional lead acid and AGM or deep cycle since they have different charging characteristics? Or do they charge at the same rate regardless what's connected?

The equalization that happens is very slow. I would not worry about it. Yes if you connect a flat battery to your cranking battery and the engine is not running it will slowly drain the main battery and you may not be able to start the car. This is very dependent on time and battery condition and why automatic type isolators are preferred over manual solenoids or master switches.

Battery types can be mixed and their charge rate and % of charge would again depend on the alternator output. (Voltage and Regulator).

Try keep them at least similar in size and capacity and have the alternator checked for output. 14.3V is ideal.

Hi Derek
Does this apply to the Bi 80?

Cheers
Jack

The Bi-80 is automatic and is also adjustable.

You can adjust the kick in voltages to prevent 'chatter'



Regards

Derek.

Hi Derek (Sorry ti hi-jack your thread Ben)

Derek, do you have any experience with the alternators on the D4D Prado's? My charge rate is only about 13.6 volts. I had it to an auto elec who said it was too low. Took it back to Toyota who said all was fine and most new cars are charging at about that rate. I am not convinced.

Cheers

Andrew

Well, how about that!!!

Add that to the list of alternators that do not charge at 13.8 plus volts all day.

Its time all the 12 volt/dual battery experts recognise that these alternators are causing a total rethink on how to charge an auxiliary battery.

Toyota would say it is within spec for your starting battery to charge. They are not interested in supplying 13.8 to 14.3 volts to your auxiliary battery. Many new cars have micro chip controlled regulation and will cycle back the charge voltage to 13.5 to 13.6 volts at engine operating temperature. You would need to do an aftermarket modification to increase this voltage to enable your auxiliary battery to charge. If it is under warranty you may need ask and get it in writing that you can do it and still keep your warranty. Try use a RACQ or NRMA approved auto electrician. (or similar in your state)

Hi feral

The important thing is to know your charging system and if it needs work or adjustment have it done. The percentage of alternators that may need adjustment work is very low but fitting a simple volt meter inside the cab is a great way to see exactly what is going on at any time.



I have fitted a in-line voltmeter to my fridge and I can see exactly what voltage is inside the fridge rather than the plug, socket, switch or cable.



Regards


Derek.

Thanks Derek,

Let me tell you my story from 'in the field'

I like to research, research & research some more. I then agonized over which best AGM auxiliary charging methods to install. I constantly monitored my alternator more months to find massive voltage fluctuations dependent on ambient temperature. I would be 14 plus volts at startup to move down to as low as 13.2v. I have actually measured 12.9v @ 38 odd ambient temps.

I listened to these 12 volts expert and they tell me my alternator is suspect. With the other evidence I concluded that it was not. All this was for preparation for a dual battery setup for our Central Australia trip. I went overboard in the specification and used all proper equipment ie. 18.9mm sq. instead of recommended 10mm sq.

The auxiliary battery was setup to power Engal fridge, laptop & van fridge so all up amp draw would be about 15amps. We only wanted power to keep everything going when we stopped to see the sights.

Even after driving for 5-7 hours why was my auxiliary battery read 12.4v at best? I even used a battery charger and that was on for 4-5 hours before it went into float.

So, at Alice we changed the alternator @ $700 plus fitting. Guess what? I had the same voltage problems on the way home. The dual battery setup was a complete failure. I have checked and rechecked all wiring and equipment. Same results.

Since then I have converted to the inverter/charger setup. I now have 12.9v even after a couple of days at rest.

I NEVER saw my 120amp aux. battery at 12.9v using the alternator.

Hi Feral

Yes some alternators / regulators are not up to the job. What do you drive and what make is the alternator ?

Regards

Derek.

Hi Feral

Yes some alternators / regulators are not up to the job. What do you drive and what make is the alternator ?

Regards

Derek.

Andrew

What is the maximum voltage you see when you first start your engine in the morning. If it is over 14.2V and drops to 13.6V when you are down the road and up to operating temperature then your alternator is working correctly. The temperature compensation in the regulator is doing what it is designed to do. This is the "Many new cars have micro chip controlled regulation and will cycle back the charge voltage to 13.5 to 13.6 volts at engine operating temperature" that Derek referred to in FollowUp 7. There is nothing new in this - my 1940 Austin 8 had it - it was in the form of a bi-metal strip in the electro-mechanical regulator in those days. There is nothing magical about the sensor in the modern regulators, probably just a temperature dependent resistor that is in one leg of a voltage comparator - a common piece of circuitry in modern control circuitry.

I would advise against doing anything to overcome this temperature compensation. If you do you are likely to overcharge and kill your starting battery. This was known long before my Austin 8 was designed and every vehicle I have had since then had temperature compensation in its regulator.

PeterD

I would agree with temperature control but would like to see constant voltage after warm up of 13.8V

Cool car by the way. Had to GOOGLE it.



Regards

Derek.

Derek

I had two of them. The first was a tourer, the second was a roadster. Never got to own a sedan of coupe.

PeterD

>Hi Feral

>Yes some alternators / regulators are not up to the job. What do you drive and what make is the alternator ?

>Regards

>Derek.


At this stage I don't believe the manufacturer of vehicle has anything to do with it. The car is a 2000 model and the distance travelled was 130,000 k's when the alternator was changed.

But the alternator is 110 amps.

With this sort of amperage it should have charged my AGM battery with no problems at all.

I believe with today's new alternators and the ideal 100% fully charged AGM battery is unachievable using a battery controller.

I was trying to establish what regulator it has and the charge voltage etc.

At Minus 20 degrees, 13.8 volts will seriously undercharge a battery.

At 60 degrees, 13.8 volts will chronically overcharge the same battery.

I find it amazing, considering the number of sensors in modern cars, that they don't all have a temperature sensor on the battery, as well as the Alternator. If they did, then taxi owners wouldn;t have to relocate batteries into the boot.

There you go, they beat me to it.

If your FULLY charged (rested and disconnected) battery only reads 12.6, you have a problem.

I do not understand this idea of "equalise." An alternator is just a voltage source and a battery connected to it will accept a charge if that voltage source is large enough. The regulator in the alternator simply adjusts the output in accordance with the expected requirements of the cranking battery (which varies with the temperature under the bonnet.) Once the battery isolator cuts in both batteries are simply being charged. The amount charge in each will vary with their state of charge and a number of lesser factors.

Back in the good old days when we just had flooded batteries we were taught of a figure of 2.2V/cell (or 13.2V for a 12V battery) This was the voltage, above which was required to be applied to a battery before that battery would accept any charge. When an alternator ceases charging, the battery terminal voltage falls below this value - generally to or less than 12.9V. If a battery requires more than 13.2V before it accepts any current, connecting 2 batteries will not produce any current flow between them (unless one battery is very dead.) Therefore you will not get any "equalisation" under these conditions either.

PeterD

>Two batteries connected to together will NOT equalise in charge.

Interesting. I had never given it much thought and merely assumed they would. As it happens; I currently have access to a whole _stack_ of calibrated battery type test gear :) I'll try and find time to do an experiment to test the above statement and data log the process in a manner I can post here.

How about the following:
2 x 7Ah AGM batteries
One fully charged
One 50% discharged
Connect via a shunt for 24 hours and data log the shunt voltage at 1 minute intervals
Perform a constant current discharge on both batteries to 10V5 to establish their final charge

What do you reckon Mike?

Mike Harding

I'd be interested to know the results. I always thought they would start to equalise.

I have 3 batteries.
1 x Cranking battery, is a 80ah Delkor Deep Cycle battery
2 x 100+ah AGM's wired in parallel with 32mm cable. (effectively 1 x battery)

Battery isolator between Cranking battery and AGM's is a Rotronics.

With 12.6v (only 1 decimal place showing) on the Cranking battery and 13.0v on the AGM's.
However when they are connected via a (10a) cable connected to the two inlet bolts on the Rotronics, which effectively bypasses the isolator and joins the two battery systems together as only one battery, the two Voltage gauges will equalize instantly.
I know because I checked it today :-))

Mainey . . .

Mike use an ammeter and try 2 batteries of different age, I've been educated into using 2 new batteries in parallel and they will act as one and not need to equalise . barnray

Mainey re FollowUp 5

All you did was to take the surface charge off the AGM battery. There would be no significant current flowing between the two batteries after a few seconds and the AGM battery would not have lost any significant capacity.

PeterD

Yes, but the point I was making was the original Voltage numbers DID change.
The "Voltage numbers" were exactly the same after a short period of time, as the two battery systems equalised.

Mainey . . .

Mainey

All you did was to remove the surface charge off the AGM batteries. What was the voltages you measured when you left the batteries for 8 or more hours. After all we have instructed you you will surely know that you should leave batteries to rest after any charge or discharge operation before any voltage readings become meaningful. What you measured immediately after your experiment had little meaning.

PeterD

Peter,
All I was showing was the voltage numbers DO change, NOT why they change!!

7.40AM, measured the Cranking and AGM battery, at rest they are: 12.67v and 12.79v respectively.

10.20AM, Started engine and both quickly went to 13.98v, were still charging slowly a few mins later.

1.45PM, attached my '10a mini jumper lead' and batteries equalised instantly @ 12.81v.

Mainey . . .

Correction.

Voltage equalised not the batteries or SOC.

Derek,
I think your just getting very pedantic, as SOC is not mentioned anywhere and the TERMINOLOGY "battery equalised" is that used by the thread instigator: ben_gv3 who asked:-> ""........What happens when the secondary batt is very discharged and then connects to the circuit, won't the 2 batts now "EQUALISE" thereby dropping the primary voltage down? ""
The batteries 'equalise' by having the Voltage in each battery being equal.

Is like saying a car is out of petrol !!
we all know the petrol is NOT in the car, but in the petrol tank.

Less technical terminology is relitively simple to understand.

Mainey . . .

Sorry if you don't understand. Let me explain it in your terms.

If you equalize the load on a truck so that it rides level you will move the load from one side to the other. You would not tilt you head and equalise the load visually.

Derek, as I said your only being pedantic :-)

Mainey . . .

Mainey

The term "equalise" as applied to batteries is nothing like this thread is talking about. Rather than cut and post large amounts of text read it yourself in part 9.1.4. of http://www.batteryfaq.org/

If you go there you will see that equalisation of batteries is done to return each cell in a battery back to being the same SOC. All you did in your test was to put some surface charge on each cell of the lower charged battery so that the terminal voltage of the two was the same for a short time. If you had waited for the normal resting time you would see how much charge you added to the flatter battery. I doubt that you could then measure any significant difference.

Quote "All I was showing was the voltage numbers DO change, NOT why they change!!" All you did was to show you could change the terminal voltage of the battery for a short time, not that you can equalise the batteries which means making the SOC of the batteries the same. You have proved nothing. Derek is not just being pedantic.

PeterD

If you connect two batteries together, then the voltage on both HAS to be equal.

I have no idea why you would call this "equalising" two batteries, unless you meant the "state of charge will equalise".

Let's get some RELEVANT FACTS into context....
If we are talking about is my post: 555164 follow-up #10

The post is about the Voltage of TWO (2) battery systems wired in parallel by a small 10 Amp mini jumper cable.

It reads: ""1.45PM, attached my '10a mini jumper lead' and batteries *EQUALISED* instantly @ 12.81v.""

It "literally" means the VOLTAGE of the TWO (2) BATTERIES are MADE EQUAL.

It does NOT mean the batteries were "equalized" as is stated in the LINK you have posted because as you and also Derek would be very well aware you require to use an ELECTRICAL CHARGER to CHARGE the (single) battery to EQUALISE the battery CELLS, which is not the same as equalizing the Voltage of two (2) individual batteries connected by a 10 Amp mini jumper cable.


# Then read Derek’s reply 7 of 9, Answer ID: 289686 #

""Just plugged the van with fully charged AGM into the car with a fully charged wet cell, via a 6m 6mm2 twin core cable and Anderson plugs.
Seems to start to *EQUALIZE*……. When I have time I will do and log a test.
Batteries do *EQUALIZE* over time guys""

Yes, Derek as I posted above, the battery Voltage will *EQUALIZE* !!

Hope that clears up some misunderstandings.

Mainey . .

"How about the following:
2 x 7Ah AGM batteries
One fully charged
One 50% discharged
Connect via a shunt for 24 hours and data log the shunt voltage at 1 minute intervals
Perform a constant current discharge on both batteries to 10V5 to establish their final charge

What do you reckon Mike?"



Mike H - please do this realworld test - too many 12 volts posts are based on "I read somewhere that . . . "

Here is the test I did to convince myself that the two-buckets-connected analogy does NOT apply to two connected batteries.



I connected a fully charged new AGM 80 Ahr battery to a good fully discharged (to 10 volts) wet-cell starting battery. The MAXIMUM current that flowed for a few SECONDS was 32 amps, but reduced to 7 amps after 1 minute.

The total charge transferred from AGM to Wetcell was only 10.7 ampHours after being connected for 2 HOURS, this will not affect the AGM's starting ability !

Keep in mind this was a worst-case test for charge transfer - a fully charged AGM has an open-circuit voltage of 13.0 volts but a wetcell only has a 12.6 volt open-circuit voltage. You would get LEAST charge transfer if you had a charged wetcell connected to a discharged AGM.

Ahhhh, cleared it up.

Thanks for that.

Again, I'm no guru, but I believe the batteries will be connected very shortly after engine start, regardless of the discharge state of the primary battery.

The VSR is connected to the "+" terminal of the primary battery, as is the alternator. When the alternator's 14v hits that terminal, the VSR see's it and reconnects.

Alastair

Unless your starting battery is severely discharged, your alternator voltage will be over the cut in voltage of the isolator within a few seconds. That is why the so called "smart" were designed - to give the starting battery a little more time without the load of the auxiliary battery on the alternator.

As for your seond sentence - suggest re-read the posts above.

PeterD

Must say that is my gut feeling too but Mike R knows a bit about the mysterious workings of electrons :) so I'd like to test the assertion before contesting it - what do you reckon about the validity of my proposed experiment?

Mike Harding

Ah yes, electrons! Those horny little beggars whose sole purpose in life is to reach meca (the positive battery terminal).

In fact, electrons are the exact reason that batteries must equalise. Whenever there is a voltage differential, electrons will flow (current). This flow stops when the differential becomes nil. Wahla! Equalisation.

Emmm... yes... but it isn't quite that simple - Ohms Law doesn't always rule. Check out "tunnel diodes" for one example and we won't even begin to discuss what happen as plasma develops (mainly 'cause I don't understand it! :)

Mike Harding

Your right, I thought we were discussing batteries directly connected in parallel.

I'll assume that comment is sarcastic?

Indeed batteries in parallel is what we are discussing and my problem is that despite 30+ years designing electronic "stuff" I have not come across this issue before and because batteries are, essentially, a chemical device I don't understand them very well: so, it may well be, they exhibit characteristics I am not aware of in specific situations. I am not aware of any creditable experiments or publications upon this particular area (if you are, please tell us and we can wrap this issue up quickly) which is why I would like to perform a scientific experiment to investigate what happens when two batteries of different charge state are placed in parallel. I have outlined an experiment methodology; do you agree with it?

It seems to me this forum frequently looses sight of the fact that debate upon these issues should not be about who is the most clever but rather about advancing knowledge for us all. I would rather learn I am wrong today than continue down a false path for the next 10 years.

Mike Harding

No Mike, no sarcasm here. I was talking about a system directly connected, no VSR. My bad. I'm interested in your test results.

"In fact, electrons are the exact reason that batteries must equalise. Whenever there is a voltage differential, electrons will flow (current). This flow stops when the differential becomes nil. Wahla! Equalisation. "

- current flow will stop when voltage is equal, but that doesn't mean charge is equal in both batteries.

To measure the of charge of a battery based on it's voltage, I have to wait many hours. The corollary does NOT apply (if I hold the voltage of two batteries at the same level for several hours, it will not mean the charge will equal out).

The maximum voltage a full battery can put out is 12.7 volts - have you ever heard of a charger that works by putting out 12.7 volts ???

The chemical reactions have a hysteresis - you have to have a higher voltage to charge a cell than what it can put out when discharging.

You can fully charge an AGM battery with 13.8 volts if you're not in a hurry - but if you discharge it, even at low current, it can't put out more than 13.0 volts.

"Batteries do equalise over time guys."

Gday Derek,
Its easy to test that current flows, so the battery with the higher voltage loses charge, and the voltage becomes equal.

But I think the question is whether the lower voltage battery is actually getting charged, or whether we are just losing 1.5amps as heat or inefficient losses. "People" have argued that lead acid batteries will not accept charge until the voltage is greater than 13.2V.

What do you think?

Hi Phil

I am actual doing the 'TEST' as I type. I have a 12 a/h SLA on charge at 13.8V and is full. I have another 12 a/h SLA and it is connected to our discharge protector and has a 50W globe draining it down to the auto switch off of 11.3V.

I will then allow them to settle and take voltage readings. I will then join the 2 via a Steca solar regulator and see how much is transferred from one to the other over 12 hours. I will then take voltage readings of the 2 again and then via the Steca and the 50w globe drain them both and see what a/h each one gives me.

The Steca is not absolutely a precision instrument but will give us an idea within 10%.

I think I already know the results but could be wrong. I am expecting about a 3 to 5 amp transfer from one to the other and a system voltage of 12.1V and when I disconnect them I fully expect one to rise very slightly given they were only linked for 12 hours.

Regards

Derek.

Results of equalisation test.

2x 12v 12 a/h SLA batteries.

Battery A (Fully charged) Battery B (Discharged to 11.3V)
Time Volts Amps Volts
10.30PM 13.2 . . 11.7 (Allowing recovery of 20 min)
10.35PM 12.6 3.0 12.3 (Joined via Steca PR2020)
10.40PM 12.6 2.2 12.4
07.00AM 12.6 0.0 12.6

Steca showed transfer of 2A (No decimal point available on this unit and based on the results below I think it closer to 2.5A)

Load test. Done on Steca PR2020 to auto switch off

Battery A Battery B
11.3 and 7 a/h 11.6 and 3 a/h

Summary:

The Steca switches of the load when state of charge is below 30% or 11.1V and battery B switched off earlier than battery A due to a lower state of charge.

The test shows that batteries do equalize but not perfectly as the voltage required for transfer is not available in battery to battery equalization. Voltage equalized but not the capacity or state of charge and this transfer was half of what would be expected in ‘true’ balancing of the charge and capacity. Although done on small batteries and over a short space of time we can apply these results to larger systems.

1) Batteries do equalise but only transfer about 30% of their SOC or capacity to the other battery.
2) Batteries require a higher voltage to recharge and absorb current.

Battery B is currently on charge after the above test and is absorbing charge at a high rate. I will time the full recharge and post it later.

14.0v 12A 0 mins
14.0v 10A 10 mins
14.0v 5A 30 mins
14.0v 3.9A 60 mins

Derek,

So the voltage equalises, but the state of charge does not.

I guess that confirms that joining two batteries together (and not charging them) is a waste of power.

Thanks for adding a bit of science to this. I would expect that wet cells would behave the same.

It would depend on where your load is connected. If the transfer of 30% SOC happens there are still advantages by connecting a discharged camper battery say to your car aux that is fully charged from a earlier drive. This would be an advantage if you camp like I do and have a compressor fridge in the camper. This enables the car to help with the load of the fridge and also bring the camper battery up. (Just a little).

Phil, when the two batteries are joined (in parallel) the TOTAL *AMPS* of the two batteries *combined* will then drive the accessories, not only the Amps available from just one battery.

When the vehicle is started the two batteries are then CHARGED as one battery.

Mainey . . .

Gday Mainey,
I'm assuming (and may be wrong) that the transfer of power from one battery to another is inefficient, and that when you hook up a discharged battery to a full one, that you will lose a few Ah in the process. Same way as normal battery charging is inefficient (eg you put 110Ah into a battery, to increase its capacity by 100Ah). Hence, wasting power.

we can't work this out from Derek's test, because capacity was not measured on a full battery, and on theat size battery, it would be nice to have another decimal place.

If you join 2 fully charged batteries, there is no transfer, so theres no loss. And yep, they will always be charged as one - as both batteries will get 14V.

Cheers
phil

Ignore the current rig description & photo. I have changed from the Paj to a LC100 but the details are the same.