Stop/start...regen...smart Alternator... Dc-dc Charger For Leisure Battery Or Not?

[mmi]

Got a little too excited on this. The link Measuring State-of-charge - Battery University suggests that AGM type of battery produces slightly higher voltage than the flooded ones. The attached table seems to align with the statement.
View attachment 26493
The table is a stripped down version (specific gravity readings omitted) of a larger table on site batteryfaq.org

It’s been down to –25C up here so found out that it’s time to correct my earlier post above about a table showing batteries open circuit voltage dependence on temperature.

Took an old battery, charged it, let it stabilize 20 hours (at about +5C), the voltage reading – 12.62 Volts.

Took the battery outdoors below –20C, let it cool down almost 60 hours. The voltage reading – 12.59 Volts.


Took the battery back into garage, about +5C. Let the battery warm up 24 hours. The voltage reading – 12.61 Volts. Had another look at using a calibrated meter...... fortunately the delta between the two seems to be pretty constant .


Discovered from “real” literature (1) that lead-acid battery’s Open-circuit voltage dependence on temperature is just next to none. Typically for a 12 Volt lead-acid battery about +1.2mV/deg C (for 6 cells, each 0.2mV/degC). So for the example above expected voltage difference is about 0.03 Volts (for about 25 degC temperature difference).

Reference:

(1) Linden's Handbook of Batteries, 4th Edition (edited by Thomas Reddy, 2010). Chapter 16.2.2 Lead-Acid Batteries, Open-Circuit Voltage Characteristics, pp. 16.11-16.12.

A new edition of the handbook will be available soon: Linden's Handbook of Batteries, Fifth Edition (edited by Kirky W. Beard, 2019), 1200 pages. McGraw-Hill Education, ISBN: 9781260115925. Scheduled publishing in May-2019.​

 

[Dilbert]

The default Victron charger temperature compensation setting is set at -16.2mV per degree centigrade for a 12V battery.

 

[mmi]

The default Victron charger temperature compensation setting is set at -16.2mV per degree centigrade for a 12V battery.

My onboard charger (Defa 1204) has even steeper temperature compensation -30mV/degC. Just checked that indeed it is now floating the batteries (AGM) at 14.5V (at -15C).
User manual of CTEK D250SA states having temperature compensation of -23mV/degC.

These all seem to align with what is stated about the need in the internet:

Full article ---> AGM Charging : Technical Support Desk
Another article ---> Charging at High and Low Temperatures

 

[mmi]

Two months has passed in the darkness and in temperatures from 0C down to -30C.

Auxiliary battery is connected through CTEK Smartpass 120 – essentially just a kind of one-way split charge relay (not a DC-DC charger stepping up voltage for aux battery charging).

Usually before starting the engine batteries are discharged using Webasto coolant heater to warm up the engine and the cabin. Total current draw approx. 13 Amps for 20 mins.

Regular runs – 30 mins, 1 hour and a few up to 3 hours.

The observations:

Alternator always stays on charging batteries at steady 14,8 Volts. Occasionally alternator drops voltage for a few times for a moment (about a minute) down to 13,8 Volts. This happens seemingly random intervals from 20 mins to 2 hours. However, during those “dropouts” the current flow into batteries does not significantly change – thus pretty much indicating they have reached steady float charge state. Also the current into the batteries eventually “stabilizes” down to less than 1 Amp when doing long runs (1+ hours) thus indicating batteries have reached (almost) fully charged/saturated state.

Even during the dropouts when voltage drops down to 13,8 V regenerative braking does not activate - alternator does not raise the voltage during engine braking - there is no extra boost into the batteries. Obviously when the voltage is held at 14,8 V the “distinctive” regenerative braking can’t take place.

The above is true even setting off with definitely fully charged batteries. Charged with on-board temperature compensated charger (from EHU) which eventually kept the batteries floating at 14,5 V (at -15C) for more than 20 hours. Also T6 battery management reported battery charge level of 100%.

However, all the above is true only temperatures below +5C (approx.).
----

Recently had a few warm days, temperatures again slightly above +5C. The charging regime seemed immediately return back to the “normal”. The voltage “floats” at range approx. 13,3-13,8 V and during engine braking gradually (at steady rate of 0,5V/sec) raises to 14,8 V.

Interestingly there seems to be only these two modes and the transition point seems to be tied to outdoor temperature. I was expecting that the change would have been more gradual between the modes. Actually I was expecting charging voltage to go further up with lower temperatures, but even at -30C still charging at “only” 14,8 V.

 

[Lowlec]

Hi MMI . . . .




Agreed and no, but i have retested the battery with a separate meter, but a good call and ill do that test.




Agreed, thats what i thought and would expect . . . .

.



Agreed, again it all makes sense on paper..

.



Agreed again . .



Yep, totally . . . same here, we wanted to fully understand the setup before connecting any heavy loads. . . . .

so, just this morning i done another test . . . . . and as you can see the batteries are not balanced . . . why? - i have no idea?


this is the OEM main starter battery . . . . . .

View attachment 26403


this is the readout after a nights worth of resting . . . .

View attachment 26404

so,
SOC @ 78%,
12.46v
SOH @ 100%

this is the facoty AUX battery . . . . . . . .

View attachment 26405

and the readout . . . . .

View attachment 26406


so,

SOC @ 48%,
12.28v
SOH @ 92%


As you said above, i dont make sense, but it should do?
i have no idea why the batteries are so far out of balance, maybe because the AUX feed cables are thinner and longer? . . . . i just dont know.


but the testing does prove the point that for some reason the AUX battery is always under charged / ., . ., , ,. ,. ,. dont know why though.


No heres the realy interesting thing . . . .

this morning i refitted the REDARC and these are the readouts just now after a day out working . . . . .

this is the CTEK readouts . . . .

View attachment 26407

ignore the fact they are at 60% odd as I've been working on the van for a couple of hours with the LED lights etc running . . . . but look at how close the balance is now!!


and heres the volts readout from the BM2 of the AUX battery . . . .

View attachment 26408

again it shows a marked improvement and increase in charge and capacity . . . . . . . . . .


so tatally agreed with everything you said above, but the testing seems to show otherwise . . . . . . . .

plus may other members having issues with a less than fully charged AUX battery when using the OEM relay or a VSR setup . . . . . ??

and also i have personally witnessed the inrush of current (with a clamp meter) from the AUX battery back over to the starter battery with a clamp meter as @Loz showed on his smart current meter when the starter battery is lower than the AUX battery....


The only conclusion i have is that that even though you would expect both batteries to be the same, the loads on the van demand current. . . . .

this should come from the alternator when the engines running, but because euro6 setup shuts off the smart alternator that current demand is sourced from both batteries via the relay.

The ECM monitors the SOC of the starter battery but is not accounting for the possible 50% off that currant draw from the AUX battery when the engine is running 50% Aux & 50% starter..

so im assuming that the EMC is not accounting for the 50% of supplied current back flowing from the AUX battery to supplement the starter battery when the smart alternator is not generating enough amps . . .

I think the ECM is just watching for the volt drop when high loads are switched on and only generates enough current to overcome the voltdrop raising the voltage to its preset level . . .


Now, i think the Aux battery is low on SOC because its not seeing its 15amps bulk/Absorption charge current for 2-3hours to bulk it up........its just seeing pulses of 15v under regen and because the ECM is seeing the NET average voltage of both batteries and assumes all is well.....


Now when you add the REDARC into the setup it has effectively a 1way diode to stop any back flow of currant from the Aux battery to the starter . . . . . . so now any availible currant is used to increase the SOC of the AUX battery.

it then uses the 3stage process to charge the Aux battery . . . .

so my conclusion is that the ECM is not factoring in the back flow of currant from the Aux battery, and just working from data from the starter currant shunt which effectively is only monitoring 50% of the available battery "bank" when the relay or VSR is engaged and connecting both batteries together . . . . . . . and dont forget the smart alternator is not shunted either . . . . .so the ECM is not metering out the current in amps generated from the alternator . . . . . only the voltage to overcome the volt drop. . . .


Thats my take on it all anyway and welcome new ideas or thoughts. . . . . . . .

I converted a brand new transit sport in 2013,fitted an aux battery oem split charge relay (euro 5) and paid fords £100 for bcm to recognise the new setup!.one thing I noticed was that after the aux battery was installed all of the electrical loads were now linked to the aux battery with critical loads only on the main....the starter motor, hazard warnings and the radio system.so I done some tests and found the auxiliary battery was always at a lower soc than the main battery after a day or two,purely down current on connected loads and courtesy lights etc!....
I now have 2 x t6’s,my works van 66 plate,has had battery problems from day one,the battery light comes on,on the dash board whilst driving,taken it back under warranty,VW can’t find anything wrong,but they did say the battery is undersized for the van,after another flat battery last time to get it changed

 

[travelvolts]

Well, you wouldn't expect to see any regen if the battery is at 100% whatever the temperature!

 

[Dellmassive]

I converted a brand new transit sport in 2013,fitted an aux battery oem split charge relay (euro 5) and paid fords £100 for bcm to recognise the new setup!.one thing I noticed was that after the aux battery was installed all of the electrical loads were now linked to the aux battery with critical loads only on the main....the starter motor, hazard warnings and the radio system.so I done some tests and found the auxiliary battery was always at a lower soc than the main battery after a day or two,purely down current on connected loads and courtesy lights etc!....
I now have 2 x t6’s,my works van 66 plate,has had battery problems from day one,the battery light comes on,on the dash board whilst driving,taken it back under warranty,VW can’t find anything wrong,but they did say the battery is undersized for the van,after another flat battery last time to get it changed

have you a got a couple of pics of the batterys you currently have?

 

[Weeked]

I think Renogy sort out the Bluemotion thing and regen breaking and leisure batteries issue:

Plus it has low temp cut off and variable voltage charge based on temperature. I think I will give it a go.

 

[Dellmassive]

I think Renogy sort out the Bluemotion thing and regen breaking and leisure batteries issue:

Plus it has low temp cut off and variable voltage charge based on temperature. I think I will give it a go.

yep . . . all detailed over here >

Dc-dc Charger (for Leisure Battery) -- How I Done It --

Lithium Lifepo4 12v Batteries - - - Time For An Upgrade ? - - -
What Solar Panel & Controller ?
Battery Monitoring -- How I Done It --

 

[travelvolts]

Two months has passed in the darkness and in temperatures from 0C down to -30C.

Auxiliary battery is connected through CTEK Smartpass 120 – essentially just a kind of one-way split charge relay (not a DC-DC charger stepping up voltage for aux battery charging).

Usually before starting the engine batteries are discharged using Webasto coolant heater to warm up the engine and the cabin. Total current draw approx. 13 Amps for 20 mins.

Regular runs – 30 mins, 1 hour and a few up to 3 hours.

The observations:

Alternator always stays on charging batteries at steady 14,8 Volts. Occasionally alternator drops voltage for a few times for a moment (about a minute) down to 13,8 Volts. This happens seemingly random intervals from 20 mins to 2 hours. However, during those “dropouts” the current flow into batteries does not significantly change – thus pretty much indicating they have reached steady float charge state. Also the current into the batteries eventually “stabilizes” down to less than 1 Amp when doing long runs (1+ hours) thus indicating batteries have reached (almost) fully charged/saturated state.

Even during the dropouts when voltage drops down to 13,8 V regenerative braking does not activate - alternator does not raise the voltage during engine braking - there is no extra boost into the batteries. Obviously when the voltage is held at 14,8 V the “distinctive” regenerative braking can’t take place.

The above is true even setting off with definitely fully charged batteries. Charged with on-board temperature compensated charger (from EHU) which eventually kept the batteries floating at 14,5 V (at -15C) for more than 20 hours. Also T6 battery management reported battery charge level of 100%.

However, all the above is true only temperatures below +5C (approx.).
----

Recently had a few warm days, temperatures again slightly above +5C. The charging regime seemed immediately return back to the “normal”. The voltage “floats” at range approx. 13,3-13,8 V and during engine braking gradually (at steady rate of 0,5V/sec) raises to 14,8 V.

Interestingly there seems to be only these two modes and the transition point seems to be tied to outdoor temperature. I was expecting that the change would have been more gradual between the modes. Actually I was expecting charging voltage to go further up with lower temperatures, but even at -30C still charging at “only” 14,8 V.

Could it be connected to using more onboard equipment like Heater blower, De icing, headlights etc?

 

[travelvolts]

I asked Victron why the new Orion TR DC DC chargers don't have LTD and they said that as this feature is built in to the BMS in their batteries it is unnecessary. Ouch.

 

[Dellmassive]

I asked Victron why the new Orion TR DC DC chargers don't have LTD and they said that as this feature is built in to the BMS in their batteries it is unnecessary. Ouch.

Yet they offer the feature in the MPPT solar range, and the BMV712 range..... so I dont get it.... surely it just a bit of firmware programming?

Now we have Renogy and Voltronic with the feature built in...... so lets see if Redarc and Victron up there game.

 

[andys]

I think Renogy sort out the Bluemotion thing and regen breaking and leisure batteries issue:

Plus it has low temp cut off and variable voltage charge based on temperature. I think I will give it a go.

To be fair, all DC/DC chargers sort out the Bluemotion/regen thing, it’s what they’re for. But yes the LTD is worth having if you’re going lithium, so long as your solar array is small enough, or you follow some of the tips above for disconnecting while driving n

 

[Weeked]

I have a 2018 T28 panel van - I'm pretty sure I have the smart alternator . The question is do I have to connect the IGN wire? The device already has a voltage sensing relay incorporated. (I just ordered this renogy)

 

[andys]

I have a 2018 T28 panel van - I'm pretty sure I have the smart alternator . The question is do I have to connect the IGN wire? The device already has a voltage sensing relay incorporated. (I just ordered this renogy)

I would have thought so, can't see how a voltage sensing relay would be any good with a smart alternator.

 

[Dellmassive]

I have a 2018 T28 panel van - I'm pretty sure I have the smart alternator . The question is do I have to connect the IGN wire? The device already has a voltage sensing relay incorporated. (I just ordered this renogy)

yes,

if it had a leisure battery from factory then you will have a engine run signal under the seats . . . . .

if not take some pics of what you have and well suss it out . . . .

(but most likely if you have a dumb VSR you will need a IGN feed for a DC-DC on a T6)

 

[Weeked]

No leisure from factory so I guess I can take the signal from the DUB unit somehow. Car is still under warranty so not sure what can I alter without messing up the warranty.

 

[bmc054]

Apologies if Im butting in but I have two red cables taped together under the passenger seat I think the larger one is from the e box do you think the smaller diameter one would be suitable for the signal to the renogy ?
Thanks

 

[Dellmassive]

Apologies if Im butting in but I have two red cables taped together under the passenger seat I think the larger one is from the e box do you think the smaller diameter one would be suitable for the signal to the renogy ?
Thanks

Take a couple of pics of what you have, then we will be able to help out.

 

[bmc054]