Mr Sargent vs Mr Victron

[Insider]

Installed 2xVarta LFD90 batteries about a week ago and let the 90W solar panel charge them up via the Victron 75/15. All happy so far. They settled in at about 12.85V at night when the sun had gone done. Little use daily so you can see the amount of top up they had received in the screenshot. Decided we're going to use the camper tonight so wanted to turn on the fridge. Connected the mains up to the camper and turned on the fridge. I have a Forte so there is a Sargent PX300 battery charger. The Victron was already on Float. What has surprised me is that the Victron has gone back onto Bulk when the EHU is in place. That leads to 2 questions.

What is the logical explanation for this? Has the current draw on the fridge caused a voltage drop across the system and the Victron interprets this as a battery that needs to be charged?
Even with a logical explanation is it bad for the batteries?

Thanks in advance
Rory

 

[poppycamper]

Sorry hate tae see a post go unanswered BUT i cant answer it cause I don't understand wot u are asking
YIP, maybe just me being thicko but the fact u got no replies says I ain't.
Goog luck

 

[Raul]

Yes, the victron has a threshold voltage below float, that will trigger re bulk. No harm to the battery.

 

[TheCaller]

The Victron appears to be doing what it should. The battery voltage has dropped to 12.81, quite a bit below the Victron float voltage.

The question is - why? If the PX300 charger has also picked up that the voltage had dropped below its float, you would expect it to be pushing the voltage to the high 13 - low 14v region. The Sargent charger's float voltage is 13.6v, so it should also be in the bulk charge state. The fridge will be working flat out to get it cool. If it's a 3-way fridge, the heater element will be at least 120w, so drawing around 10A from the charger's available 20A. There should be spare capacity, so to see such a voltage drop makes me suspect inadequate cable size somewhere - a very common failing in UK conversions according to many posters on here.

 

[autorouter]

If it's a 3-way fridge, the heater element will be at least 120w, so drawing around 10A from the charger's available 20A.

It's most likely that the fridge, if 3-way, is running on gas rather than 12V power.

The 3amps could be the solar controller contributing all it can, but maybe not enough power to raise the battery voltage over 14V. Maybe the Sargent charger doesn't kick in until the voltage drops below a threshold, so it's not contributing anything yet.

I'd say everything if working OK. If there's more battery drain and the voltage starts to fall, the Sargent will take over. This is exactly what you want, right? The solar providing power first, and if it's not enough, the mains charger takes over.

It's a general motorhome problem - how do you charge a battery when it's not isolated on a bench, but has loads attached that may or may not need power?

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[Insider]

TheCaller - I hadn't thought about inadequate cabling but no reason to suspect my van is any different to most others unfortunately.

autorouter & Raul - The fridge was definitely on 220, gas was turned off but I think that the current draw from the Sargent to power the fridge and the voltage drop across the cabling caused the solar to kick in. My fear was that the batteries which had been already gone onto float were being over charged but I think the solar was part supplying the fridge rather than charging the batteries.

Thanks to all

Rory

 

[TheCaller]

The fridge will be working flat out to get it cool. If it's a 3-way fridge, the heater element will be at least 120w, so drawing around 10A from the charger's available 20A. There should be spare capacity, so to see such a voltage drop makes me suspect inadequate cable size somewhere - a very common failing in UK conversions according to many posters on here.

It's most likely that the fridge, if 3-way, is running on gas rather than 12V power.

I must have been half asleep when I wrote that! I know I didn't post it until after 9am, but I actually wrote it in the early hours of the morning. I'd been looking at compressor fridges earlier in the evening & I think my brain was still in that mode. That's my excuse anyway!

Given that the van is plugged into EHU & sticking with the assumption that it is a 3-way fridge, it shouldn't have been running on either 12v or gas - it would be running on its mains heater element. So the battery draw would be minimal & there shouldn't be any significant voltage drop, however undersized the wiring.

I know the Sargent float voltage is 13.6v, because it says so in the manual. I don't know how far below that the voltage has to drop before it restarts bulk charging. Maybe it is lower than the 12.81v shown on the Victron Connect display. Clearly Victron think bulk charging should be restarted at that level.

There are good reasons why a mains charger would have a lower switch-on voltage than a solar controller. A solar controller is never going to be able to provide as much power as a mains charger (unless you have an RV roof plastered with solar panels), so it makes sense to start charging before the recharge job gets too big. Secondly, as mains electricity is more often that not paid for by the kWh, it makes sense to use any available solar in preference.

As everyone has said, it looks as if things are working as designed. You would only have a worry if the voltage dropped much below 12.5v before the Sargent charger kicked back in.