Split charge relay (Sargent EC176) and Smart alternator - tested and definitely worse than useless. (1 Viewer)

rwg

Sep 7, 2021
219
479
Funster No
84,021
MH
Benivan 120
Exp
Since 2021
So, this all started with me wanting to get into a position to change to a Lithium battery in our Benivan. In order to do that I needed to be sure that all the things that might charge the battery are compatible with lithium. That means...

* Solar controller - I've replaces the original with a Votronic which has a Lithium option and also keeps both batteries topped up - no problem here
* On EHU mains charger - the charger built into the Sargent EC176 is a 'dumb' 13.8V constant charger. Not perfect, but it shouldn't damage a lithium battery (although it won't hit full charge either)
* Finally the mystery... charging from the alternator when driving via whatever is built into the van - is this Lithium compatible???

There isn't a separate split charge relay or B2B charger - it's all handled internally by the EC176 unit and there isn't any real documentation on how the EC176 handles charging when driving, so some experiments were needed.

In theory there are a number of ways that it *could* be happening

* B2B built in - unlikely , this is a low end budget unit
* Voltage sensitive relay - not supposed to be very good with smart alternators
* D+ driven relay - again not supposed to be very good with smart alternators
* Either of the relay options with an added diode system to prevent flow back from the leisure battery to the vehicle systems when driving and the alternator voltage drops

Rather than take things apart and try to figure out what the circuits were in the Sargent unit, I decided to fit a bluetooth battery voltage monitor - one of these : Amazon product - and go for a drive.

Screenshot_20220914-153433.png


Up until 9am, the solar controller was gradually topping up the leisure battery to 100% as the sunlight brightened. Then from about 9:30 until just after 10am we were driving, about 20 miles mostly dual carriageway. The voltage at the leisure battery really changed around while driving, going up to about 14.3 V when the smart alternator was kicking out its maximum of 15V, but dropping to 12.6V when accelerating and the smart alternator was practically off.

What does this tell us? That the system is running off a simple D+ driven relay, connecting the leisure battery and the vehicle electrics together when the engine is running. Yuck.

Two things were interesting...

Firstly the leisure battery was definitely at a lower charge level (12.6-12.7V) at the end of the trip than at the start - this means that with the smart alternator, the system isn't actually charging the leisure battery while driving - instead, at least on this sort of trip, the leisure battery is supporting the van electrics :(

Second, the highest peaks of the alternator at 15V or so aren't getting through to the leisure battery - this is probably just voltage drop in the wiring, which is reputed to be fairly lightweight in British built vans. Those peaks of 15V getting through would have been a problem for a lithium battery, so saved by the crummy wiring...

So, my conclusion is that for now the best thing to do is to disable the split charging system on the EC176 completely, even with the current lead battery, since it doesn't seem to do any good whatsoever - discharging the leisure battery while driving rather than charging it. When I do switch to lithium batteries, leave it disconnected and maybe fit a B2B system at some point in the future.

I've seen a few suggestions on how to do this disconnection of the split charge in the EC176

* Sargent have a document somewhere online for a similar system that recommends a relay to disconnect the vehicle battery when the engine is running
* Another thread on here suggested pulling the 20A vehicle battery fuse in the small fusebox behind the drivers seat

The first is a bit complex and I tried the second and it also cuts off the vehicle battery from the solar charger. However... if you pull the 20A fuse labelled vehicle battery in the EC176 itself, it cuts off the split charge system but leaves the solar controller connected.

With the vehicle battery fuse removed from the EC176, things work like this
* Leisure battery unaffected by driving - our return trip from about 1:30pm until 2pm in the graph above shows this
* Control panel shows 'vehicle battery disconnected' and will loose power if leisure battery goes off
* Solar panel charges vehicle battery
* Electric step still retracts on engine start (good)
* Fridge on 12V - untested, expected to work as there is a separate fuse for the fridge 12V
* Obviously you would be unable to run the habitation electrics from the vehicle battery - this is only an emergency 'no power' thing, so you could re-insert the fuse in the case that this was required....

The only thing that is a bit of a problem is the control panel not showing the vehicle battery voltage - it's nice to check that from time to time. I'm tempted to try replacing the fuse that I have removed with a 1000 ohm resistor - that would limit current flow to/from the vehicle battery to a handful of milliamps, preventing the charging or discharge of the leisure battery but should still allow the control panel to see the vehicle battery voltage. Worth a try :)

cheers,

Robin
 

Kannon Fodda

LIFE MEMBER
Feb 26, 2019
2,416
7,303
Seek and Ye May Find
Funster No
58,768
MH
Autotrail V-line 540
Exp
I Make Schoolboy Errors!
You don't say what your mh make model is which may help some with guidance.

My Autotrail Vline 540 may be similar but I don't think has smart alternator. Pull the fuse behind driver seat which stops the charging loop to EC176 relay. May stop the use of engine battery for emergency habits use, but if you have extra capacity from the lithium why need that. Fit vanbitz battery master and stop worry of the habit battery voltage. Leave the solar on leisure charge only (my van had weird two way switch to swap solar from leisure to engine which I removed but needed a link for the D+to retract the step. Since wired solar direct to battery not via EC176 to get better charge as wires fitted very thin.
 
OP
OP
rwg

rwg

Sep 7, 2021
219
479
Funster No
84,021
MH
Benivan 120
Exp
Since 2021
Ah yes, sorry, it's a Benivan 120. The UK Benivans are actually made by AutoTrail, so it probably has a lot in common with yours - we certainly had the odd two way switch for the solar panels which is now gone, replaced by the dual battery capable charge controller.

I expect the wires from the solar controller to the battery are thinner than they should be - I can get to the wiring under the floor of the cupboards (where the solar controller is), but haven't worked out how to get new/replacement wires down through the wall to the battery in the locker below without making a mess...

cheers,

Robin

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Jan 28, 2008
9,946
17,637
Dovercourt, Harwich, UK
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1,353
MH
Renalt burstner
Exp
7 years campers before that
Firstly the leisure battery was definitely at a lower charge level (12.6-12.7V) at the end of the trip than at the start - this means that with the smart alternator, the system isn't actually charging the leisure battery while driving - instead, at least on this sort of trip, the leisure battery is supporting the van electrics :(

12.7 is a fully charged battery any voltage above that is being supplied by one of the chargers
 
OP
OP
rwg

rwg

Sep 7, 2021
219
479
Funster No
84,021
MH
Benivan 120
Exp
Since 2021
Hmm, maybe 12.7 if you have left it a long time since charging with no load, but my graph shows that it took 9 hours from 7:30pm when the solar charger cut out to until 4:30am for the battery to drop down to 12.80V, and it was still at about 12.75V at 7am when the solar started to charge it again. In that context, a 12.6-12.7 reading after half an hour of driving is a clear indication that the battery has been under net load rather than net charge during the drive :(

Anyway, I made the 'fusistor' by deliberatly blowing a 5A fuse, then soldering a 1K ohm resistor across the blades

PXL_20220915_142120340.jpg
Popping this into the 'Vehicle battery' fuse holder did just what I hoped - allowed the vehicle battery voltage to show on the control panel
PXL_20220915_142348047.jpgPXL_20220915_142330967.jpg
However, also as expected, you cannot run the system from the vehicle battery any more, as the resistor blocks any significant current from flowing. This is what happens if you try :)

PXL_20220915_142809694.MP.jpg
Also the panel cuts out if you pull the leisure battery fuse, so not enough power coming through to keep the panel alive. Maybe you could fudge this with a lower value resistance, but honestly not really bothered enough to try.

I will check the fridge runs OK on 12V on our next trip, but I am expecting it to. Hopefully mission accomplished - a minimal impact way to cut off the split charge system.

I can think about getting that lithium battery now ;)

cheers,

Robin
 
Jan 3, 2015
149
171
Hartlepool
Funster No
34,617
MH
Swift Kontiki 884
Exp
Since 2017
Got this from Sergent when I asked if my 2022 Swift Kontiki had a B2B, apparently it doest and only has a split charge relay. This mod must be done when fitting a B2B which complicates things

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Mar 30, 2022
51
90
Banbury, Oxfordshire, UK
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Tugging since I could drive, now joining the dark side šŸ˜šŸ˜‰
Got this from Sergent when I asked if my 2022 Swift Kontiki had a B2B, apparently it doest and only has a split charge relay. This mod must be done when fitting a B2B which complicates things
Brilliant, thanks for posting this. I also have a 2022 Kontiki and reconfiguring Leisure battery charging is on the top of my list of things to do. Was there any further info like wire sizes etc?
Have you done your mod yet?
 
Jan 3, 2015
149
171
Hartlepool
Funster No
34,617
MH
Swift Kontiki 884
Exp
Since 2017
No I'm fitting a smart shunt so I can actually read what current the split charge is putting in, I will then decide if I'm going to fit a B2B. Another thought is also go OTT on Lithium, the most I'm ever off grid is 4 or 5 days so 400a/h of Lithium and I wouldn't need to worry about recharging when off grid ill just recharge when I'm home
 
May 7, 2016
6,607
10,306
West Sussex
Funster No
42,951
MH
Carthago Compactline
Exp
Since 2003
If the base vehicle has a smart alternator it needs a B2B (sometimes called a charge booster) for the leisure battery. Autotail should know this and have provided one instead of relying on a split charge relay. This issue has been known since 2015.

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Jan 3, 2015
149
171
Hartlepool
Funster No
34,617
MH
Swift Kontiki 884
Exp
Since 2017
If the base vehicle has a smart alternator it needs a B2B (sometimes called a charge booster) for the leisure battery. Autotail should know this and have provided one instead of relying on a split charge relay. This issue has been known since 2015.
It has a smart alternator, Sergent are telling me the split charge will give 20a but im guessing thats not at tickover it will be out on a drive
 

Steve and Denise

LIFE MEMBER
Sep 26, 2011
5,047
13,057
Spalding LINCS
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18,300
MH
A Class Carthago
Exp
Since 2008
So, this all started with me wanting to get into a position to change to a Lithium battery in our Benivan. In order to do that I needed to be sure that all the things that might charge the battery are compatible with lithium. That means...

* Solar controller - I've replaces the original with a Votronic which has a Lithium option and also keeps both batteries topped up - no problem here
* On EHU mains charger - the charger built into the Sargent EC176 is a 'dumb' 13.8V constant charger. Not perfect, but it shouldn't damage a lithium battery (although it won't hit full charge either)
* Finally the mystery... charging from the alternator when driving via whatever is built into the van - is this Lithium compatible???

There isn't a separate split charge relay or B2B charger - it's all handled internally by the EC176 unit and there isn't any real documentation on how the EC176 handles charging when driving, so some experiments were needed.

In theory there are a number of ways that it *could* be happening

* B2B built in - unlikely , this is a low end budget unit
* Voltage sensitive relay - not supposed to be very good with smart alternators
* D+ driven relay - again not supposed to be very good with smart alternators
* Either of the relay options with an added diode system to prevent flow back from the leisure battery to the vehicle systems when driving and the alternator voltage drops

Rather than take things apart and try to figure out what the circuits were in the Sargent unit, I decided to fit a bluetooth battery voltage monitor - one of these : Amazon product - and go for a drive.

View attachment 664370

Up until 9am, the solar controller was gradually topping up the leisure battery to 100% as the sunlight brightened. Then from about 9:30 until just after 10am we were driving, about 20 miles mostly dual carriageway. The voltage at the leisure battery really changed around while driving, going up to about 14.3 V when the smart alternator was kicking out its maximum of 15V, but dropping to 12.6V when accelerating and the smart alternator was practically off.

What does this tell us? That the system is running off a simple D+ driven relay, connecting the leisure battery and the vehicle electrics together when the engine is running. Yuck.

Two things were interesting...

Firstly the leisure battery was definitely at a lower charge level (12.6-12.7V) at the end of the trip than at the start - this means that with the smart alternator, the system isn't actually charging the leisure battery while driving - instead, at least on this sort of trip, the leisure battery is supporting the van electrics :(

Second, the highest peaks of the alternator at 15V or so aren't getting through to the leisure battery - this is probably just voltage drop in the wiring, which is reputed to be fairly lightweight in British built vans. Those peaks of 15V getting through would have been a problem for a lithium battery, so saved by the crummy wiring...

So, my conclusion is that for now the best thing to do is to disable the split charging system on the EC176 completely, even with the current lead battery, since it doesn't seem to do any good whatsoever - discharging the leisure battery while driving rather than charging it. When I do switch to lithium batteries, leave it disconnected and maybe fit a B2B system at some point in the future.

I've seen a few suggestions on how to do this disconnection of the split charge in the EC176

* Sargent have a document somewhere online for a similar system that recommends a relay to disconnect the vehicle battery when the engine is running
* Another thread on here suggested pulling the 20A vehicle battery fuse in the small fusebox behind the drivers seat

The first is a bit complex and I tried the second and it also cuts off the vehicle battery from the solar charger. However... if you pull the 20A fuse labelled vehicle battery in the EC176 itself, it cuts off the split charge system but leaves the solar controller connected.

With the vehicle battery fuse removed from the EC176, things work like this
* Leisure battery unaffected by driving - our return trip from about 1:30pm until 2pm in the graph above shows this
* Control panel shows 'vehicle battery disconnected' and will loose power if leisure battery goes off
* Solar panel charges vehicle battery
* Electric step still retracts on engine start (good)
* Fridge on 12V - untested, expected to work as there is a separate fuse for the fridge 12V
* Obviously you would be unable to run the habitation electrics from the vehicle battery - this is only an emergency 'no power' thing, so you could re-insert the fuse in the case that this was required....

The only thing that is a bit of a problem is the control panel not showing the vehicle battery voltage - it's nice to check that from time to time. I'm tempted to try replacing the fuse that I have removed with a 1000 ohm resistor - that would limit current flow to/from the vehicle battery to a handful of milliamps, preventing the charging or discharge of the leisure battery but should still allow the control panel to see the vehicle battery voltage. Worth a try :)

cheers,

Robin

This is what I did to make things simple for charging my lithium,
firstly fit a B2B with a D+ trigger.
Then fit a five pin relay from your battery to your Sargent unit N/C with a D+ trigger,
when your engine is running the B2B will look after your battery charge, and the relay will be open disconnecting your feed from the Sargent and batter, when the engine stops the relay closes and connection from batty to Sargent is restored.
That is the way I did mine over a year ago and itā€™s worked faultlessl.
 
Aug 1, 2021
834
4,819
Pembrokeshire, UK
Funster No
83,135
MH
Auto-T Expedition 66
I suspect that the OP rwg probably has a dumb alternator rather than a smart one, and that his early interpretation of the voltage graphs has misled him.

We have a 2021 Euro 6 Autotrail Expedition which is essentially identical to the Benivan PVCs that come off the same line at Grimsby that rwg has. Ours doesn't have a smart alternator. See this thread -

Thread '2021 Autotrail PVC - smart alternator?' https://www.motorhomefun.co.uk/forum/threads/2021-autotrail-pvc-smart-alternator.257871/

Like the OP, I'm not actually sure how much the Sargent EC176 brings to the party in terms of hab battery charging whilst driving - I've tried setting the fridge to off rather than 12v to see if I can determine a difference from my own voltage charts when driving, but couldn't discern anything conclusive. (The fridge normally stays really cold when switched 12v though so I suspect that this is getting the lion's share of the output from the split charger rather than the battery). The split charger definitely contributes something though as my (Victron) solar controller goes from bulk to absorption and then float quicker when driving than if stationary and on solar alone. My guess it's only a few amps output though.

PS. rwg - I'm enjoying your threads - you've made one or two discoveries and mods that we've also done. Currently giving serious thought to your wheel arch/ locker mod. šŸ‘

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May 7, 2016
6,607
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West Sussex
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42,951
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Carthago Compactline
Exp
Since 2003
It has a smart alternator, Sergent are telling me the split charge will give 20a but im guessing thats not at tickover it will be out on a drive
It is more than that, the voltage will go down even when driving. The voltage will go up most when you are slowing down, the idea being that most of the charging is done when the engine is being pushed by the wheels and the alternator can recover the engine energy that would otherwise be wasted by braking. The engine battery is monitored and kept at a lower voltage so that there is room to store the energy that would otherwise be wasted. You might get 20A but probably only for brief periods. On tick-over you may even get current flowing from the higher voltage leisure battery back through the split charge relay into the engine battery which is being held at an artificially low voltage.
The split charger definitely contributes something though as my (Victron) solar controller goes from bulk to absorption and then float quicker when driving than if stationary and on solar alone. My guess it's only a few amps output though.
Perhaps this is caused by the short periods when the alternator is charging at full whack, the solar controller may sense the higher voltage and be tricked into moving down to absorption and float.

Without a B2B the systems monitoring the leisure battery may be getting false information and conversely the systems monitoring the engine battery may be getting false readings too. The two sides need proper separation which is what the B2B does provided the old relay is not causing a loop.
 
Apr 27, 2016
6,553
7,414
Manchester
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42,762
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A class Hymer
Exp
Since the 80s
It has a smart alternator, Sergent are telling me the split charge will give 20a but im guessing thats not at tickover it will be out on a drive
It's a bit misleading to say it will give 20A. A smart alternator's function is to keep the starter battery at a lot less than full charge. If you parallel your leisure battery to it with a relay, it will get the same treatment. That's why a Battery-to-Battery (B2B) charger should be fitted for the leisure battery.

Edit: just seen Pausim's post, with more detailed explanation.
 
Last edited:
OP
OP
rwg

rwg

Sep 7, 2021
219
479
Funster No
84,021
MH
Benivan 120
Exp
Since 2021
Barti Ddu glad you are enjoying the posts. I am currently working on a plan to add a b2b and replacement mains charger and locate all the charging kit with the battery in the newly opened up locker space of possible.

I can confirm that my van definitely has a smart alternator. As well as the leisure battery voltage logger I have an OBD port connected speedo display on the dashboard because the fiat speedo is so poor. This gadget also shows the vehicle battery voltage in real time. Stick you foot down or go uphill and it drops back to around 12.5v or so as the alternator reduces power. Take your foot off the accelerator or brake and it will go up to 15v. It also does stop start when it feels like it.

Cheers, Robin

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May 7, 2016
6,607
10,306
West Sussex
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42,951
MH
Carthago Compactline
Exp
Since 2003
Barti Ddu glad you are enjoying the posts. I am currently working on a plan to add a b2b and replacement mains charger and locate all the charging kit with the battery in the newly opened up locker space of possible.

I can confirm that my van definitely has a smart alternator. As well as the leisure battery voltage logger I have an OBD port connected speedo display on the dashboard because the fiat speedo is so poor. This gadget also shows the vehicle battery voltage in real time. Stick you foot down or go uphill and it drops back to around 12.5v or so as the alternator reduces power. Take your foot off the accelerator or brake and it will go up to 15v. It also does stop start when it feels like it.

Cheers, Robin
15V would be a bit too high for a LiFePO4 battery. Another good reason to fit a B2B.
 

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