148 replies to this topic

[Vic Harder]

Makes sense.  Also good to know how this works in practice, that is, having the Lithium batteries act as a trickle charger for the truck batteries.  I am surprised at how much drains though.  Makes me wonder if the "trickle" might be too strong, and the truck batteries are being over charged/cooked?

[craig333]

I don't think its that. I've had a drain on the truck batteries for a long time. I'd need to disconnect the second truck battery, Pull a terminal off the battery to measure amperage and hope nothing goes fubar when its disconnected. Then spend a few hours pulling fuses hunting down the drain. Is that a good excuse not to get in there and do it? No. Mostly I'm just too lazy and not motivated enough to do it. Maybe talking about it will motivate me. 

 

When I spent a week camping and not using solar on the truck batteries it just barely turned over enough to start. Considering how expensive batteries are now I want them to last a long time. Plus I no longer can just turn the switch and jump it off the camper batteries. I'm assuming if the truck batts were and low and the lithium being happy to discharge a lot of amps would probably blow the fuse on the 10ga wire, or worse.

 

But you're right, the Lipo4 wants a higher charging voltage than the truck batts. Trickle charging this way is probably something I shouldn't do often.

[cs0430]

With ~200 watts of solar on the roof, would it be recommended I upgrade the Redarc BCDC 25amp model that will come with my lithium kit to their 40amp model?  Or some other model?  Our F250 will have the 410amp alternator option and we want to ensure driving time is being fully maximized to charge the single 135amp battery.   

[Vic Harder]

With ~200 watts of solar on the roof, would it be recommended I upgrade the Redarc BCDC 25amp model that will come with my lithium kit to their 40amp model?  Or some other model?  Our F250 will have the 410amp alternator option and we want to ensure driving time is being fully maximized to charge the single 135amp battery.   

How many AH of battery?  Recommended solar is 2x AH, so 200W of solar = 100AH of battery.  And actually, that rule of thumb was developed for flooded lead acid batteries, so it's more like 4xAH now.  The idea being able to recharge fully in one day.  So given 100AH draw overnight (that's lots), to recharge 100AH you need x Amps for x hours.  10A for 10 hours or 20A for 5 hours, etc.  The latter is more practical in my experience.... not too many places that get 10+ hours of usable sunshine in a day.

 

In other words, most people don't have enough solar.

 

OK, assuming a 200AH (??) battery bank, you want to be able to charge at the same rate as 4x solar. 200AH in 5 hours = 40A.  

 

So yeah, an upgraded DCDC that can pushout the amps you need might be a good idea.

[Jon R]

My approach was a little different because i live in the PNW with a lot of forest and cloudy weather. After doing a detailed estimate of my daily energy use:

I sized my battery based on how many days I wanted to stay out camping in the PNW in the trees (basically no solar output) without starting the truck, and decided on 200 ah of battery to assure at least 5 days of endurance with no charging.

I sized my solar array based on wanting to recover at least a day’s worth of utilization (about 35 ah for me) with cloudy but open sky from April-September in the PNW. I decided on a 400 watt panel array, which fits nicely between the vents on my Grandby, and a 30 amp MPPT controller/charger.

I decided I wanted to be able to recover two day’s worth of utilization with 2-3 hours of driving, so I decided on a 30 amp dc to dc charger.

So for me my solar system sizing was directly related to daily energy utilzation and only indirectly related to battery size selection.

[cs0430]

That all makes sense.  My question was more of - between 200w (16.7A although I'll never see all of that in reality) of solar and having power come from the truck, is it likely I'll be maxing out the Redarc's 25A capacity and be leaving charging "on the table" when driving - I won't be maximizing what could go into the battery.  

 

The 200w of solar was just based on one single panel I'll likely put on top.  Based on usage if I start running low on the battery I'll look at adding a solar briefcase to supplement the roof solar when camping.   

[Vic Harder]

That all makes sense.  My question was more of - between 200w (16.7A although I'll never see all of that in reality) of solar and having power come from the truck, is it likely I'll be maxing out the Redarc's 25A capacity and be leaving charging "on the table" when driving - I won't be maximizing what could go into the battery.  

 

The 200w of solar was just based on one single panel I'll likely put on top.  Based on usage if I start running low on the battery I'll look at adding a solar briefcase to supplement the roof solar when camping.   

Just make sure that your setup includes a real battery SOC monitor, like the Victron Smart Shunt.  That way you will know if you are running low.

[Vic Harder]

So for me my solar system sizing was directly related to daily energy utilzation and only indirectly related to battery size selection.

Practical.  I think I was assuming battery size selection was already done based on utilization.

[craig333]

I was a little disturbed to see Will Prowse suggest a 20amp DC/DC charger after I already installed my 40amp unit. It sure does charge fast. A trip to dog park charges my battery right up (from an overnight dishcarge). I've been happy with how my 250w of solar does. I guess I need a trip to the PNW and see how it does