Warwick XL heating system

While we are on the subject maybe you electric savvy guys can help me out.
My 2024 Symbol has 2x100ah lithium batteries & 180w of solar panels.
The fridge is compressor, therefore only electric, I will probably watch a small amount of telly & the other usage will be the heater fan, lighting & whatever the Sargent system draws.
I’m wondering how long to exist off grid, any ideas??
I have this aversion to campsites.

While we are on the subject maybe you electric savvy guys can help me out.
My 2024 Symbol has 2x100ah lithium batteries & 180w of solar panels.
The fridge is compressor, therefore electric only & the other juice used will be the heater fan,  maybe a bit of telly, lighting & whatever the Sargent system draws.
How long could I exist off grid??
I have this aversion to campsites!

Whoops!!, didn’t realise we were on page two!!

mikemelson wrote:While we are on the subject maybe you electric savvy guys can help me out.
My 2024 Symbol has 2x100ah lithium batteries & 180w of solar panels.
The fridge is compressor, therefore electric only & the other juice used will be the heater fan,  maybe a bit of telly, lighting & whatever the Sargent system draws.
How long could I exist off grid??
I have this aversion to campsites!

I wasn't aware they had put compressor fridge in Symbol.

As an approximation, you will need to carry out a DC load inventory:-

Create a Table and record in the first column the equipment name.
In the second column record what the load is for the equipment under test by taking a reading in Amps from the control panel (check it is zero before switching on the equipment)
In the third column record in fractional hours how long you think you will realistically be using that equipment in a 24 hour period.  
In the fourth column, multiply the figures in each rows to obtain the Ampere/Hours for each equipment.
Repeat for remaining equipment, the more you include the greater the accuracy.
Total column four to give you an idea of how many Ampere/hours you are using in a 24 hour period.
Take the manufacturer's recommended Depth of Discharge figure for your battery, if you can't find it use a nominal figure of 80% and divide it by your 24 hour Ampere/Hour Total.

As an example
Battery = 200Ah
80% of 200 = 160Ah
Load = 40Ah
Estimated worst case = 160/40 = 4 Days (assuming that you haven't underestimated the load and you have no solar input)
This is worst case as we haven't taken into account how much charge the solar panels are replenishing the batteries but this is difficult to average as it is weather dependant.  

You could extend the calculation to include the charge generated by the solar panel on an average day in the UK which would extend your off grid time, best of luck with that.

Good answer Monty but you have not addressed charging input from the engine, presuming that there is an intention to drive the van occasionally. I suspect that the OP does not wild camp in any one place for more than a day or so.

I don't know but I presume that the subject van (as a 2024 model) is now fitted with a B2B charger so it should be relatively easy to add back the charger rating for each hour driven. I have no experience of B2B chargers but my understanding is that say a 30 amp B2B will charge at a pretty steady 30 amps for as long as it needs to, i.e. for as long as the LB's will take a bulk charge and presuming that the Smart alternator system maintains at the least a voltage sufficient to keep the B2B triggered.

So if I am correct a vehicle with B2B will put back its rated charge current every hour, or near enough.

The Bargee wrote:Good answer Monty but you have not addressed charging input from the engine, presuming that there is an intention to drive the van occasionally. I suspect that the OP does not wild camp in any one place for more than a day or so.

I don't know but I presume that the subject van (as a 2024 model) is now fitted with a B2B charger so it should be relatively easy to add back the charger rating for each hour driven. I have no experience of B2B chargers but my understanding is that say a 30 amp B2B will charge at a pretty steady 30 amps for as long as it needs to, i.e. for as long as the LB's will take a bulk charge and presuming that the Smart alternator system maintains at the least a voltage sufficient to keep the B2B triggered.

So if I am correct a vehicle with B2B will put back its rated charge current every hour, or near enough.

Good point, that does indeed need to be considered.

So many variables

Monty-Plym wrote:
....
So many variables

and there will be a variation in load between winter and summer.  In the summer there will be much less lighting and probably less TV and no Whale heating fan but the compressor fridge will use more.  A constant will be the EC700 at about 7Ah per 24 hrs.

The Bargee wrote:I have no experience of B2B chargers but my understanding is that say a 30 amp B2B will charge at a pretty steady 30 amps for as long as it needs to, i.e. for as long as the LB's will take a bulk charge and presuming that the Smart alternator system maintains at the least a voltage sufficient to keep the B2B triggered.

So if I am correct a vehicle with B2B will put back its rated charge current every hour, or near enough.

Exactly that. A DC-DC charger is a voltage amplifier, and will output the necessary voltage and current to charge the leisure battery regardless of the vehicle battery voltage, within limits. This is quite a lot of power to take from the vehicle battery, but the alternator will detect that and increase its output to maintain the vehicle battery charge level. There are safeguards to reduce the charging current in stages if the vehicle battery drops below certain levels, but with a healthy battery in normal use you would expect to get the full output all the time the engine is running, until fully charged.

The Sargent B2B is 20A, perhaps that is what is fitted. It has a similar charging profile (bulk/absorption/float) to what mains chargers typically have. And perhaps depending on configuration you’re also getting the solar charge on top of that.

Paulmold wrote:
I wasn't aware they had put compressor fridge in Symbol.

They certainly have in this case Paul.

But Auto Sleepers  were always liable to change the spec on a whim!

My 20 year old Symbol was a bit of a one-off, it had additions not seen on other examples.

I read the spec on website after you posted and yes you do indeed have a compressor fridge. The last van they put one in was the Stratford.

I changed my fridge in the WXL to a compressor fridge, probably one of the best mods I have done.  Now it doesn't matter if I park on a slight slope, it still works and I don't have to mess around with vent shutters.  I sold my old one on Gumtree and recouped 70% of my outlay, well worth it.

Monty-Plym wrote:I changed my fridge in the WXL to a compressor fridge, probably one of the best mods I have done.  Now it doesn't matter if I park on a slight slope, it still works and I don't have to mess around with vent shutters.  I sold my old one on Gumtree and recouped 70% of my outlay, well worth it.

Yes, good move!  We changed all our hire boats to Engel compressor fridges back in 1984 and never looked back. No more customers complaining of defrosted food after mooring in a shallow spot on a list! I am just waiting for our three-way to flicker so as to have an excuse to change it.

Edit: Having said that perhaps I should be changing it now whilst it is still working and saleable, but I do so hate the aggravation of selling things!

The latest Symbol is described has having a large compressor fridge and freezing compartment.  Typically how many Ah will that consume over 24 hrs?

At a guess about the same as an EC700 or less!

When we removed the absorption fridges from our hire boats (run on gas only) and installed 12 volt compressor fridges we noticed no significant increase in load on the batteries, i.e. we had no noticeably greater incidence of service calls for flat batteries and we did not find we had to increase the battery or charging capacity. The same applied when we stopped fitting 12 volt compressor fridges in new boats and moved to domestic 230v AC fridges run from Victron inverters. I have no figures, just an impression from running 30 hire boats for a long time!

The vital point to note is that the wiring to the fridge needs to be well sized. Calculate the run (there & back) and the load, see what is recommended from the charts and then go up a couple of wire sizes. Most problems with 12 volt installations of all sorts stem from undersize wiring, i.e. excess voltage drop.

A compressor fridge is the ideal use for solar power: when the fridge is working hardest the sun is at its brightest!

7Ah or less sounds very good.  I got the impression they used much more than this.  I do find their greater efficiency appealing with no outside vents wasting energy and creating draughts in the van.

Caraman wrote:7Ah or less sounds very good.  I got the impression they used much more than this.  I do find their greater efficiency appealing with no outside vents wasting energy and creating drafts in the van.

It sounds too good to be true, and it is. The smallest compressor fridge I can find on the Thetford website (84 litres, 975x418x486) quotes average power consumption of 26.6 Ah per 24 hours, so a bit more than 1A. The largest one quotes 46.5 Ah per 24 hours. Which is quite a lot, on top of all the other power demands. My friend Rich who has been converting a large Sprinter to a 4 berth camper van from scratch for a couple of months now has got 3x230Ah lithium leisure batteries, a 3 kW inverter and 530W of panels. And no gas for anything. Induction hob, no oven, diesel space and water heating, compressor fridge. It's much easier when you start with a blank piece of paper.

Yes, sorry, I might have got my hours and days addled in my last post but I would certainly expect a figure of some 25 to 30 AH average per day. I see one Thetford model quotes an input of 5 amps, which sounds about right and is of course 120 AH when multiplied by 24, but of course the duty factor is probably only +/- 25% depending on how often you open the door, ambient temperatures, how well insulated the fridge is etc etc. All I can say is that we never had a problem with the boats. Our smallest boats (42' narrow boats) had 180 AH of domestic battery capacity and 35 amp alternators and they ran for 20 years with no significant battery issues. No solar, no EHU.

The real problem on these vans (for the more adventurous types) is the lack of charging. On a bright sunny morning the other day my 100 watt solar panel was shoving out 1.5 amps after the spindly wiring and the poor quality regulator. That will change next week if I get time and it gets a bit warmer! When I bought the van the 150 amp alternator was only getting a maximum seen of 9 amps to the LB before I changed all that. All fine if you treat the van like a caravan and move it from EHU to EHU, so it works for some, and that is probably enough for the AS designers and accountants. The 20 amp fuse that was on my LB supply cable told me straight away that AS never expected more than 20 amps to get to the battery, and of course it wouldn't given the gauge of the wiring. And then of course a 100 AH battery is simply not enough except as a buffer between EHU's, and the spindly wiring everywhere does not help efficiency.

So yes, if your usage does not revolve around EHU's then it takes more battery capacity and better charging inputs, both solar and from the engine.

I'm not sure if my reasoning is correct here, can someone do a sanity check please.

My Vitrifrigo Compressor C115i fridge/freezer is rated at 65 Watts 
My 200Ah LiFePO4 battery voltage is approximately 12.5V @ 20% and 13.6V @ 100% so lets take an average of 13 Volts
To calculate current draw P (Power) / V (Voltage) = I (Current)
65/13 = 5A for 1 hours running but the fridge never runs continuously and when at temperature and its not blazing hot outside, it cuts in for approximately 20mins/hr (0.33 hours) therefore Current use over 1 hour is actually 5A x 0.33hours = 1.65Ah
Available Battery capacity = 80% of 200Ah = 160
160/1.65 = 96 hours
or 1.65 x 24 = 39.6Ah/day
96/24 = 4 days (but in reality there are other DC loads though I don't use much, water pump, lighting is LED, and I don't watch much TV)

However my battery is charged from Solar and I rarely stay anywhere for 4 days continuously so both the solar and the Smart Alternator and B2B is keeping the Hab battery charged.  I have never run out of juice.
Am I missing something here?

Its an odd one really as the 3-way absorption fridge which is all I have ever had lends itself to off-grid as it will run on gas and doesn't place significant demands on the LB and solar.  The compressor 12V fridge in some ways is ideal for those who only ever drive between EHUs as its more efficient, doesn't need outside vents and works on a slope.

Monty-Plym wrote:I'm not sure if my reasoning is correct here, can someone do a sanity check please.

My Vitrifrigo Compressor C115i fridge/freezer is rated at 65 Watts 
My 200Ah LiFePO4 battery voltage is approximately 12.5V @ 20% and 13.6V @ 100% so lets take an average of 13 Volts
To calculate current draw P (Power) / V (Voltage) = I (Current)
65/13 = 5A for 1 hours running but the fridge never runs continuously and when at temperature and its not blazing hot outside, it cuts in for approximately 20mins/hr (0.33 hours) therefore Current use over 1 hour is actually 5A x 0.33hours = 1.65Ah
Available Battery capacity = 80% of 200Ah = 160
160/1.65 = 96 hours
or 1.65 x 24 = 39.6Ah/day
96/24 = 4 days (but in reality there are other DC loads though I don't use much, water pump, lighting is LED, and I don't watch much TV)

However my battery is charged from Solar and I rarely stay anywhere for 4 days continuously so both the solar and the Smart Alternator and B2B is keeping the Hab battery charged.  I have never run out of juice.
Am I missing something here?

I think that’s more or less right. The fridge is quoted at an average consumption of 1.6A so you’re not far out there. For your use it seems like the important thing is capacity, which you have got. As you say it will be charged by the B2B anyway in a few hours so it really doesn’t matter much if the solar can’t keep the battery charged for short stays. As long as it doesn’t run out, which it shouldn’t, then there isn’t a problem. When I change my battery, I will double the capacity for the same reason.

Caraman wrote:Its an odd one really as the 3-way absorption fridge which is all I have ever had lends itself to off-grid as it will run on gas and doesn't place significant demands on the LB and solar.  The compressor 12V fridge in some ways is ideal for those who only ever drive between EHUs as it’s more efficient, doesn't need outside vents and works on a slope.

I can see the appeal for a new build, not for efficiency so much, but for simplicity. But if you already have the vents, and the gas supply, the benefits are less persuasive.

Our van (not an AS now) came with a compressor fridge and we were worried about capacity . We have a similar set up to Monty - Plym at 200ah lithium battery and I’d say our use is similar to that in his calculations. In winter we’d mostly stay on EHU sites, but when we don’t and require heating(Truma) two days is well within capacity. In addition to the heating we’d use lights/pump and charge phones:iPads. Not much TV though. Assuming virtually no solar input the B2B recharges the battery as you’ve say when we move on. I’ve not monitored it that closely so it may be the case we’d get a third day without moving.

In summer with similar use but without heating, we lose  about 10% SOC per day net of solar input.  On that basis we’d get 8 days without EHU or moving as we can discharge our battery down to 20% of SOC. Of course it depends on how much sun we’re getting and it’s something we’re unlikely to do anyway. In answer to the question about off grid use I think you could use your van indefinitely in summer, keeping your battery comfortably charged if you move every few days and especially as you have more solar capacity than us too.

We don’t have an inverter so any 240v stuff such as the Remoska or hairdryer has to wait until we get EHU. I assume if you have an inverter it uses a fair bit of battery capacity.

mikemelson wrote:

They certainly have in this case Paul.

But Auto Sleepers  were always liable to change the spec on a whim!

My 20 year old Symbol was a bit of a one-off, it had additions not seen on other examples.

I think you also said you have 180W solar and two leisure batteries? Neither of which is mentioned on the website I don't think. Is that standard now?