sieade245 avatar image
sieade245 asked

Skylla TG Charger Bulk Protection

Hi everyone. I asked a question recently regarding disabling Bulk protection mode on a Phoenix battery charger. The thread is here:

During the investigation, with assistance from Victron support staff; we found that we were able to disable bulk protection by connecting a MK2 programming lead and using VEconfigure. So that's our Phoenix charger sorted.

So following on from that, now I have the same question and problem...but with the Skylla Charger. To be clear, this is the older non-I version of the chargers. We have several models installed, all are 24V versions ranging from 24/30 up to 24/100. The boards do not have an RJ45 port so I can't try the VEconfigure trick again. There is another connector on the board which looks like an IDC type ribbon connector, not sure what this is for though. Can't see anywhere else to plug anything in. There are DIP switches but none of these are allocated to bulk protection (according to the manual).

The manual says that after 10 hours of bulk charge, the chargers will switch to float mode to protect the battery. We have not observed this behaviour with our chargers. Our chargers will instead shut off and the fail LED will flash the code for bulk protection activated. These fault codes are not in the original manual but are in the manual for the Skylla-I and appear to be the same. If the charger is switched off/on again charging will recommence for another 10 hours but then the same will happen. Luckily, most of our sites that have these fitted have remote control generators instead of mains power so as long as we monitor our battery voltages we can tell when a charger has gone into Bulk protection mode and reset the generator to carry on charging.

Example: We have a 3000Ah battery bank that was discharged to 23.5V. It took over 30hours bulk charge with a Skylla 24/100 set to 100A charge to charge this back up. During this time I had to:

1. Start generator locally and then leave site. Charger operates at 100A Bulk for 10 hours.

2. After 10 hours, remote monitoring showed that battery voltage had dropped back down to 24V, charger failed on bulk protection.

3. Remote reset generator. Battery voltage seen to increase to 26V on charge again as Skylla is reset.

4. Repeat 2 and 3 every 10 hours

It wouldn't be so bad if the charger did what the manual said and went to float mode, at least this would eventually charge the batteries back up without our intervention, (not ideal charging voltages though). We can't go any higher with our charge currents, we've got 16mm feeders and that's it, space is tight.

So is there any way to do what we did with the Phoenix chargers and disable this mode? Or alternatively make the charger go into float mode instead of failing?

Cheers, Si

battery chargingchargerSkylla
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2 Answers
Johannes Boonstra (Victron Energy Staff) avatar image
Johannes Boonstra (Victron Energy Staff) answered ·


First a bit background on this behavior of the charger. This is done as charging (with a relative high charge voltage) will destroy the battery when this voltage is applied for 10 hours or more (10 hours is already a lot!!). What happens is that mainly the positive plate will start corroding which results in a dramatically lower lifespan. So in order to prevent this, and detect a battery cell failure ) this function is built in. Therefore its important to have the charge current in balance with the battery capacity (or make sure not to discharge the battery so far the charge take too much time). By now you hope for the solution to this i guess, well i am sorry but there isnt any real option. The Skylla has a power supply mode (which would prevent stopping the charge but will always go on a specific charge voltage) or you could make a automatic reset with a timer relay on AC input which would stop/start the AC every 12 hoers or such. By far the best here would be to have more charge power (which isnt an option as i understand) or have the battery discharged less. (100A charger can do about 500Ah charge in 8 hours )

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sieade245 avatar image sieade245 commented ·

Hi Johannes. Thanks for your quick reply. The AC timer relay is a nice simple solution, I like that.

I agree, the charge current ideally would be much higher, maybe with parallal charging although this would increase our cable requirements. We have gone higher on other stations 75mm x 4 for some Quattro installations (quite difficult to wire in though with bend radius!)

I'm not too concerned about overcharging. This would require a faulty cell and for the other cells to be held at bulk voltage for an extended period of time? Although our bulk phase takes a long long time, during this time the battery voltage is less than 28.8V as it climbs up there with the cell voltages roughly equal. Absorption time is only 4 hours so at the most they would be held at this bulk voltage for only 4 hours. We have a separate system to control the generator set that will shut the set down after battery bank has reached target voltage + 4 hours

We test the cells every 12 months at 50% SOC using a HOKI cell resistance tester to try and predict cell failure or imbalance. Not foolproof method of protection but better than nothing. Normally the battery wouldn't be at such a low SOC but we had a separate fault (unrelated) on the genset so there was no way to recharge them without fixing the generator which required a helicopter etc. Quite an unusual set of cirumstances!

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ur12vman avatar image
ur12vman answered ·

I ran into this myself last night when I noticed that my chargers had both stopped working. I have two skylla ip65 units charging an 800ah lifepo4 bank on the boat. So at the dock, shore power keeps the batteries up, but if we are using lots of power they never fully charge until later in the day once consumption is down. In the unit setup menu there is "bulk time protection" but no explanation as to what this is in the manual. I needed to find this thread to understand. VE needs to revise the manual. At least there is an option to turn it off. Come on VE, its been 18 months since this thread, and the manual is still missing stuff.

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