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Regarding CAN bus regulated charging.

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When running CAN bus regulated charging the A-BMS starts to reduce the max-discharge allowed in the system when the first cell reaches "Balance voltage Start". When running solar this runs smooth and gradually the current will lower until its 1.1A and then to 0A.  But when charging high currents this phase leads to oscillating current.

Lets say you are charging an 12V system with 300A or even 400A and the BMS suddenly reduces max current to 50A or even 10A.

Then voltage will drop, and BMS goes back to 400A. And so it goes on for some time.

This is not unique for WS500, it only does what it is told by the BMS. I have seen this in other solutions where charging sources are large compared to the battery.

What I would like is an more smooth volt/current transaction from bulk to float.

Any thoughts on this?

Uploaded files:
  • WS500.jpg


This makes sense, when you are dealing with large charge parameters the PID can get a little twitchy.  It sounds like you may need to increase your Proportional and reduce your Integral and Derivative for your application and this would likely require a firmware update.  By way of this reply I have linked you to Al at Wakespeed to see if he has any ideas for you.



I have seen this before while working with BMS manufactures in proofing reliable Alternator based charging systems; the 'Twitchiness' I call it seems not much of an issue with pure electronic charging sources (Solar, AC chargers, etc); but toss in the inductive / mechanical nature of Alternators - and it results in the behavior you noted. I am also noting your comment of seeing this with other (non alternator?) high power charging sources - interesting.

We have worked with BMS manufactures on this in some cases, and the need is for the BMS to be more paced with its changes.  To allow time for the alternator to fully respond.

I do not know much about the 'A-BMS', though seem to recall hearing of it.  Trying to google it was pointless, as all I could find was articles about "A BMS"  as in "A BMS is a nice thing..."  And yes, the WS500 does respond to these changes, even if fast paced, as we dearly want to avoid tripping a BMS in a disconnect, perhaps due to battery current exceeding requested limit.

BTW, you have touched upon some of the work we do when 'proofing' BMS's - not just that it works, but what happens at EOC, what happens in Warning and Alarm phases.  What happens when loads are added and removed.  All critical to a well preforming, safe and reliable system design.





Hello Trond,

Can you post your settings from the REC ABMS?

How big is your battery bank?

Maybe I have some suggestions if you give more information.

For example it could be that your balance start is set to low.

ONE practical example I notice with high current alternators is you can not set the charge Bulk voltage to low.

Many users say if you charge lifepo4 only to 13.9V/or 14V  they are full when 13.9V is reached. My testing shows this statement is true if charge with LOW amps.  If charging with high amps, in my test 120amp, I need to set 14.2V.  Than when 14.2 V is reached, amps will quickly go down, what means the batteries are full.

With high amps, always the voltage goes down, if the charge is removed. I see this with any other charge source, not only with alternators.

You could try to do a test, make start balance 3.55,  end balance 3.6


With the WS500 and the REC ABMS you have 2 possibilities.

-1  the REC gives the charge instructions, which are different as the internal charge profile from the WS500 themself.

-2  use the internal charge profile from the WS500. Disconnect the Can-bus for a test. Set WS500 to lifepo4 profile.  The internal charge algorithm from the WS500 has plenty off possibilities to fine tune your favorite charge profile.

You can use bulk charge up to 13.9 or 14V with full 300 amps, and then the last bit off charge with lower amps, like 50amps. Look at overcharge $CPO: in the manual. It is all programmable.

With 2, you miss the nice feature from the low amps when balancing start. But probably you have solar in the system as well and the final balancing will be done through low amps from the solar.  AND probably if you have good quality cells, your cells don't need any balancing.

With 2 you can wire the ""stopcharge"" relay from the bms to the ""feature in"" from the WS500, this to disconnect the alternator from charge if one cell is too high.  With feature in you can tell the regulator to go to float.

In this float function, alternator will still deliver all  amps for the load, but will not charge the battery.

Let me know off this is usefully






A quick follow up,  we have verified this behaviors with one of our Beta testers and I have an Email out to REC -- REC and Wakespeed to work to improve the EOC handling.


And noting also, did not make the connection above of A-BMS to the ABMS from REC, sorry : - )




Has this been resolved?   I am experiencing this behaviour with my Rec Active integrated with my WS500.  Updated to the newest (non beta) firmware and I am still seeing the issue.  Makes me wonder why even bother having CAN communication if this is the result.

REC has informed us a new REC BMS Firmware will be sent to us this next week for testing.  We (Wakespeed) will be looking at this behavior as well as other noted issues around REC.


The prime benefit of CAN based linkage between the BMS and the WS500 is it allows the BMS to control the charging process -- using its Cell level insight.  And of course we use the same commutations path for advanced notice of pending disconnects as well as remote instrumentation.


My experience is that this was much better in Wakespeed V2.4.3. Then in V2.5_Beta it got worse again.

Confirmend by going back to V2.4.3 so I belive Wakespeed are on to something..


Its the same with REC FW2.6 and FW2.7.

And yes I have tried everything, set Max current to 600A, rise the "start balance" and also we charge to 14.2V.

This picture was sent to us from one of our clients (We are REC, Victron and Wakespeed dealer).

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  • WS500_jojo.jpg

We are indeed looking at current stability, esp with CAN based instrumentation and BMS 'moving targets' in a rather quick fashion (Blue line in your graph).  Most BMS's assume quick responding MPPT, and AC chargers, with no lag as associated with electro-machinical alternators!.  It is likely we will be releasing a Beta-2 in a few weeks, want to 1st to more trials with updated firmware from REC as well which we are expecting some time next week.

Thank for the note of your experience with 2.4.3 vs. 2.5.0-beta, it helps!



I have seen fluctuation amps with MPPT controllers as well.
I see also customers installations with NO fluctuation with MPPT controllers.
The fluctuation in amps I could solve the problem with re-balancing the battery cells.

I think one part from fluctuating amps has to do with cells that are out off balance.
Correct programming from REC parameters is also very important.

And a firmware update from REC could also help to get better regulation when cell are out off balance.

Short explanation why you see fluctuating amps when there is a cell imbalance:
The REC BMS send through CAN a new amp target. In a GX product this is visible under Parameter/ CCL.
If one cell reach Start balance, REC start reducing the CCL level.
Maybe REC can improve this fluctuating amps in there firmware, but to have the cells nice in balance is really important.

I monitor and have build multiply setups for customers.
I notice almost NO cell imbalance with the expensive Winston cells.
The installation that I see fluctuating Amps is with blue aluminum cased cells.

What I see with lifpo4, when cells are in balance, NOT any CCL regulation is needed.
In one example, 140amp charging ith alternator, continues gives up to 14.0/14.2V the full 140amp.
In the last few minute, the amp decrease in 1 or 2 minutes to almost zero.
This is how lifepo4 are excepting charge. NO regulation in amp control is needed.

When one cell reached earlier the programed Voltage level THEN another cell, Amps need to be controlled to avoid one cell reach Max cell voltage.

Back to the subject when charging with alternator and WS500.
Many times the MPPT is low amp, and cell imbalance will be lesser visible than with high amp alternators.

Charging with HIGH amps, any imbalance will be give problems quicker then charging with low amps.

Here comes the good point from the WS500 compare to the MPPT controller.
The WS500 can charge HIGH, full amps up to a programmed voltage, and amps can be reduce.
Check the manual and use for example bulk charge up to 13.9V/14.0V.
Then use from 13.9V/14.0V to 14.2V Overcharge mode with reduce amp, as example 20 or 40 or 80amps.

Have the REC Start balance NOT to low, I good value is maybe 3.52 and End off balance 3.55

In the above post I see that the amp fluctuation start around 13.8V, I have the feeling that in this case the Start balance is programmed to low. WHEN charging voltage is around 13.8V the REC ONLY will send a lower CCL level when ONE cell reach the Start off balance parameter.

This means OR the cells are out off balance, OR the Start balance and/or End off balance are programmed not correctly.

Below I post 3 screenshots where the battery bank is charge with around 70/80amp, with mppt controllers.
As you see the CCL is decreased slowly.
IF in this setup there was a 80 amp alternator there was probably NO amp fluctuation.
With a 250AMP alternator, it could be different, therefore I suggest to try charging with lower amps above 13.8/14.0Volt, with programming Overcharge

Iam curious, OR the above suggestions, a little higher REC settings for start balance, and the use from Overcharge in the charge profile from WS500 and  re-balancing the pack will give a better result.

Iam happy to hear some feedback on the above.

It would by nice to see more information together with some feedback.

information like:

- screenshot from the REC cell voltages, when the Voltage is at highest, just before the amp fluctuating start?
-If VRM is used, post screenshoot from CVL level

-If VRM is used a screenshot from Cell MIN and Cell MAX
- REC settings, start balnce, and end balance.

With all this info we can see or the problems are related to a imbalance in the cells.

Uploaded files:
  • mppt-1.PNG
  • mpppt-2.PNG
  • Mppt-3.PNG

Hi Ben.

Yes I do agree, balance in the cells is important, and will play an large role in how long the process will be in charging the cells.

But my 1000AH Winston bank is perfectly balanced.


And internal recistance is very low, these cells can handle 3C (3000A) charging

At 400A charging, there is o,03V difference between highest and lowest cell.

If I setup the WS500 with Lifepo4 charging program everything runs smooth.


I have start balance to 3.5V and end of charge to 3,55V. And sure, raising these even more would probably help but I belive there needs to be some improvements in the Firmware both in REC and Wakespeed side on how fast the WS500 should react to changes in the MAXD value.


I know that Wakespeed is working on improving this so I am sure it will be better in future.

I believe i am experiencing something like this as well.... ?

FYI. I have ABMS, wifi, LCD, Balmar XT170, WS500, Cerbo GX, Victron Multi's and Victron MPPT x 4 all CAN or VE connected.

With the alternator charging.. when i get to , around 98% SOC, the current still keeps creeping up until the BMS charge relay opens.

With my Solar and Victron chargers this does not happen.

I have reported this to Al at Wakespeed. He has sent the new firmware. ... but i am not sure if in need a Victron Cerbo FW update as a pre req,

also, I am on ABMS FW 2.6 where / what is 2.7 - cant see it on the REC site ?



Wakespeed firmware 2.5.0 is being released this week; and has some improvements - but there still might be work needed on the REC side for its requests, as well as refinements how the REC BMS is configured.  These type if details often come down to a given system install:  Alternator size, responsiveness, battery size, etc.  But hopeful things can be worked out to smooth response down.

In our testing we have also found that using the physical current sensing wires (Gray / Purple) attached to a physical shunt can help as well, vs. using the CAN based remote instrumentation.  One more configuration idea that might help is to use a negative number for the engine warmup delay in the $SCA command (New to 2.5.0).  This will cause the WS500 to slow down how fast it ramps up field drive and in cases with a responsive alternator and perhaps smaller battery bank perhaps could help.

On the Cerbo update:  No update is needed to the Victron equipment with regards to the WS500 & REC BMS operation.  However, 2.5.0 does have a number of refinements we made working with Victron to support their current beta release (2.90) of the Venus OS (Cerbo, color GX, etc) to include the WS500 in its reporting -- including VRM.   If one wishes to take advantage of that, then yes, a Cerbo update is needed to the 'latest release' vs. the 'latest stable release'

On the REC Firmware:  I do believe there was an intention to smooth out the change requested.  Referring to the photo above with the changes in requested current and the alternator response:  there really is not much more the WS500 can do, as it does need to respond to requests, we can not ignore them and it does take time for alternators to respond -- the overall approach for Wakespeed is to approach limits carefully, but back away quickly when a goal is changed.  The slow approach reduced stress on the mechanical side of the install while also reducing overshoot.

But not sure that would address "when i get to , around 98% SOC, the current still keeps creeping up until the BMS charge relay opens."  That sounds more like an issue with the REC Configuration -- goal and cut off points.  And/or maybe using the negative value for the warmup delay might help as well in this case?


Quote from Damian Raffell on August 2, 2022, 4:26 am

I believe i am experiencing something like this as well.... ?

FYI. I have ABMS, wifi, LCD, Balmar XT170, WS500, Cerbo GX, Victron Multi's and Victron MPPT x 4 all CAN or VE connected.

With the alternator charging.. when i get to , around 98% SOC, the current still keeps creeping up until the BMS charge relay opens.

With my Solar and Victron chargers this does not happen.

I have reported this to Al at Wakespeed. He has sent the new firmware. ... but i am not sure if in need a Victron Cerbo FW update as a pre req,

also, I am on ABMS FW 2.6 where / what is 2.7 - cant see it on the REC site ?



Post an screenshot of your REC settings. Sounds like you have set your MACVcell to low.

Have you activated DVCC in the Cerbo?

BTW, ABMS FW 2.8 is out now.

To Damian:

If your HV relays opens, there is a cell to high in voltage.

I agree with the things Trond says in previous post.

Also post a screenshot from your cell Voltage levels just before the HV trips.

If there is a tiny imbalance in the cells, you will see that with low amp charge(solar) all works correct.

But with high amp charge(alternator) the cell imbalance is visible.

You could use "overcharge" mode in the WS500, to charge lower amps above 13.9V as example also.

See explanation, in previous post above.


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