Solar again

Not 100% of the time, but you are possibly using 25A to run 3 fridges……coupled with who knows how large a wire you have to feed the 3 fridges, so the unknown is how many amps are “free” to charge the batteries.
Lots of information to be told yet….are all the fridges in your van ? What voltage are you getting at the rear of the vehicle ? What is feeding into the MPPT ?

Bricky
Although you don't mention it, the 90L 3 way must be in a caravan. Are the other fridges also in the van. Not clear there!

You didn't mention solar panels but did say about a victron 100/20/ So are the solar panels on the vehicle or the van? Best to know so people can reply appropriately.
Basically you have 100 AH of usable to 50% charge, ie normal. so the 80% to 90% seems reasonable.
More than adequate wiring, means it is bigger than recommended. Is it really?
If it is OE caravan wiring for solar then it is most likely far too small. Vans are not known to be at all generous with cable sizing and the resistance may be crippling the Victron performance.
What size is the solar panel. If a Chinese variety where the piddly output is about 3 times over stated on the label to reality, you may not be getting much from the solar through the MPPT. Only way to know is to monitor the ampere current flow into the battery between the Victron and the battery during good sun conditions. Then you will have some idea of it's performance and expected contribution to charge the battery.

The 90 litre will be sucking 15amps while running, a bit ess with cable length too long. The DCDC may be drawing or trying to draw 30 amps at times, so there is 45amps needed for most of the time. Fridge on 12v is a constant load, no thermostat there.
The vehicle if modern, will be asking for around 10 amps from the alternator to run vehicle, You didn't say what that is.
If it is a 100 amp output and a diode in the alternator is blown, the output will be reduced to 33% of it's max at best output. That would mean less than the demand. No fast charging. Is the alternator is top shape? What is it's output WHILE supplying all the gear and engine systems too.

Sounds like a bit of diagnostic testing is in order to determine amp flows in various areas so you know it is OK or not.
Without facts it is all guesstimation.
PS, $45 clamp meter to read dc operating current flows would be a good friend to have!

Thanks guys.
A bit more info.
Vehicle is a Fuso with a slide on with 2 fridges inside, and the Trailblazer in a toolbox on the tray.
The three way fridge, as mentioned is wired direct to the truck batteries through a VSR, totally isolated from the house batteries This was done professionally by a guy in Adelaide who does this as a business. From all reports he knows his stuff. Checks were made on the wiring for voltage drop....all good there. He also checked on the wiring for the MPPT which I did myself. Again all good.
Just one 150w panel on the roof, Kings. The reason for so little on the roof is we normally camp in the shade and put out a couple of portable panels.
The trailblazer draws around 5-6 amps when running. These fridges have great insulation so guess it would run maybe half the time where we are now. I think the 15ltr kings draws around 3 amps when running.
In not overly concerned, but was just wondering if the DC DC and the MPPT are confusing each other.
Cheers

Hi Bricky,

Let me state that I am not an Auto. Elec. or a 12 volt expert.

A couple of things to clarify. You say your batteries are getting down to 80 to 90%, overnight, is that Depth of Discharge, (DOD), or State of Charge, (SOC)?

You also state you are using 20 to 30 AmpHrs, is that amps per hour, or a total of 30 amps used overnight?

Continuously running AGM batteries the down below 50% SOC is not recommended. Some people argue that it has no effect on the batteries, but most experts do not recommend this.

Given that the majority of compressor fridges use between 3 to 5 amps per hour when the compressor is cycling, 20 to 30 amps per hour seems like there is a lot more current being drawn from the batteries than just the 2 fridges. If we use 3 amps per hour as the load from each fridge, that is 6 amps per hour in total from the two compressor fridges. If you pull off the road at 4:00 pm, and get back on the road at 9:00am the next day, that is 17 hours. 17 x 6 = 102 amps in total just from the two compressor fridges. You have a total of 240 amps in your house batteries. If both house batteries are at 100% SOC at 4:00 pm, and are down to 20% SOC, at 9:00 am next morning, Then something else is drawing 48 amps overnight. What other 12 volt appliances are you running overnight?

You also state that the 3 Way Absorption fridge is wired directly to the trucks 12 volt system and not connected to the house batteries, so this should not be drawing directly from the house batteries.

If your DC/DC charger is delivering 30 amps per hour, it should be able to deliver 240 amps in 8 hours of continuous driving. However, you need to deduct from this the 48 amps that your fridges are drawing out in that same 8 hours whilst you are driving. You need to check and see if the MPPT is delivering current at the same time as the DC/DC is also delivering current.

Macca.

Which DC-DC charger? Does it have a dedicated solar input? Is it expected to "play nice" as a load for the MPPT?

my dc to dc has solar input and if any amps going in, will stay on solar when motor running, if try disconnecting the solar when driving around. If the solar is separate to the dc to dc, then the dc to dc is seeing higher volts than actual battery charge state and will float or absorb rather than bulk.
disconnect solar and measure battery volts. reconnect solar and measure again, you will be measuring the surface charge the solar is putting in, and this is what the dc will be seeing too

Dont forget that some dcdc chargers wont kick in till 10-20% of the batteries capacity has been used.

I have a similar set up, though have an Enerdrive 40A dc dc charger & a Victron 100/30 MPPT, hooked up to an ATG 300Ah lithium battery. On roof of the canopy, have an LG 375w panel.
An 80L Engel upright & a 40L Engel chest fridge(as a freezer) use about 20% DOD overnight. I’ve had no battery dramas since adding the MPPT & the bigger panel. Previously had a 200w panel, but it didn’t do much.

Plan on adding 400-600w of panels to your roof & I’d be surprised if your problems won’t cease? And change to lithium batteries too!

Bob

If you have time try disconnecting one battery and running through a cycle and see how it behaves, then swap to the other battery and do the same and compare the results.
Could be as simple as a failing battery.
Your system sees your batteries as one battery, it can not see discharge of current from one battery to the other so the over all state of charge could be a lot lower than your app is thinking.

Any follow up on this one available yet?
One other thing re recharge time, it isn't as simple as power available multiplied by time equals fully charged batteries.
There are other variables in play with AGMs such as surface charge affect which in itself has a lot of variables so can not just be added to the formula as a set figure.
A 30 amp dcdc charger will not be able to force 30 amps into a flat bank of lead acid batteries till they are anywhere near fully saturated.