44 replies to this topic

[rotti]

I hope and trust the Hawk system will keep us up and running for at least 3 days in one location [with OEM double battery set up/furnace/110L 2 way].  Time will tell.

 

 

I have a 12 Hawk with the same frig and factory dual batteries. I only have a single Renogy 100w portable suitcase solar panel and on a recent nine day hunting trip I had plenty of power.  I had a couple of cloudy snowy days and cool/cold temps in the mountains of  Colorado. I used the furnace hardly at all (a big draw.....I use a good down bag) and I did "re aim" the panel three or four times a day. You should be fine.

 

Edited by rotti, 11 November 2015 - 09:59 PM.

[DrJ]

Phil,

I actually think the 160 watt zamp solar system that FWC uses now is a pretty decent setup. For the majority of people with compressor fridges and furnaces, this would be adequate. If you get less solar hours or use more power it might be a stretch, but many owners don't.

It is a big improvement from the 100 watt panel. I would assume that panel is not quite enough.

[pawleyk]

DrJ,

 

Where did you install your solar charge controller? Is it connected to the coiled 10ga in your battery box?

[DrJ]

It is mounted on the "roof" of the battery compartment. It is a 20 amp MPPT controller and seemed to just barely fit in there. I can't see the indicator lights but it works great in that spot.

[pawleyk]

Perfect. So the solar lines in the box are just direct leads from the plugs on the roof and rear wall?

[pawleyk]

Also, I seriously owe you a beer or two.

 

Thanks for all the help!

[DrJ]

Perfect. So the solar lines in the box are just direct leads from the plugs on the roof and rear wall?

 

The solar lines are direct from the solar. You can hook them up directly to the solar controller.

 

In this picture you can see the solar controller above the batteries. 

[carld]

Have you considered that you can only charge the batteries to 100%.  So if you go two days with little or no solar your starting point is at say 50% charge.  If the charge current is just a little more then you use, you may only be at 60% at the end of a full solar day.  It may take more than one full sunny day to get the batteries to 100%.  A 200 Ahr battery at 40 to 50% charge requires more than 100 Ahr (150 Ahr including camper load current) per day to fully charge them.  Not only that but because of the non-linear characteristic of the batteries you may have to apply a high voltage low current over 4 to 6 hrs to raise the battery charge from 80% to 100%.  I don't know just something to consider.

[DrJ]

I purposely sized my solar system to do just that. It could make up 100 amp hours in one day under ideal conditions.

250 watts/14 volts = 17.85 amps X 6 solar hours = 100+ amps

Collecting solar is rarely "ideal" where I camp so I also have a 135 watt portable panel that can be run at the same time.

It's quite easy to get to 100% of a 200 amp hour battery with 385 watts of solar working for you.

[carld]

It could be a little more complicated than that. The battery can only absorb so much charge depending on its charge state. Suppose you drive to a site starting in the evening and the battery is at 100% from the car alternator.  The battery discharges all evening and night and by sunrise it at 75%.  By noon the battery reaches 80%.  At this time the battery will limit the charge current and I think it can drop to maybe 200 mA or less.  For the remainder of the day ( 3 or 4 hrs) the battery will charge to maybe 90% depending on the type of charge controller.  The charge controller should bump the charge voltage up to 14.2 V during this time otherwise the battery will stay at around 80%.   Then you have another evening and night starting 80% this time and the next day at noon your at 70% charge ... then 60% on day 3 and 50% on day 4.  And this assumes that each day is a nice sunny day.    Note that adding more solar charge power does not really solve the problem since the battery limits the current based on its charge state so the extra available charge current cannot be used.  The MPPT changes the operating point on the PV voltage current curve to operate closer to the PV open circuit voltage at a low current.  Also the MPPT should try to increase the battery voltage to 14.2V to push the charge above 80%.  Increasing the battery size helps.