2nd Battery and solar choice -- more questions

[dwh]

So it looks like the CTEK acts as a battery monitor/tender which you power off your car battery to manage your isolated 2nd battery

Actually, I'm pretty sure what it actually is, is a 20a PWM charge controller that can take input power from the chassis electrical bus and step it up, or solar (no stepping up needed), to do a multi-stage PWM charge on the battery - and also has an MPPT circuit on the solar input.

(All MPPT controllers are pretty much MPPT on the solar side, and PWM on the battery side. MPPT optimizes the output of the solar, but does nothing to optimize the charging of the battery so they use PWM for that.)

I wonder if a second solar controller could simply be set up between the Solar Panel and the secondary battery, thus your getting charge options from two sources?

I doubt if it's needed, but there are ways to split solar into two different charge controllers. I recall Morningstar used to have a doc on their web site of how to do it. Something involving a diode.

I just pulled out the specs on the solar charger unit I have. In theory it could care less where the power comes from, so solar power or car power. Its max pv voltage limit is 40volts.

Yes, you could use it that way, but if you need to get your battery up to a voltage higher than the vehicle's voltage regulator will go, then it won't do that. It doesn't step up the incoming voltage like a proper DC-DC charger will. So if your vehicle's voltage regulator caps out at say 14.5v, and you need to get the battery to 14.8v, it won't happen unless you are feeding the PWM a higher voltage (solar) to begin with.

Since you would probably get more amps in a shorter time by just going straight from the engine battery to the aux battery, you'd probably be better off with a solenoid relay instead of a little PWM controller.

Max charge current is 20amps. I think all of these small units are capped at 20amps, even my shore power unit on my boat runs at 15amps. So there is probably a amp limit on the typical power load placed on your typical 12volt system to avoid battery damage.

Not usually, no. A starter can draw as much as 250a, so can a winch. A truck might have a 100a or more alternator because it might have to supply 100a of continuous load just to run the truck. Actually, when hot they are usually only good for 80% of rated power, so if the manufacturer though you might need 80a just to run the truck, they'd stick in a 100a alternator. Bigger alternators are usually an option for those who need them.

But there is nothing to limit the amp flow from the battery. That would defeat the purpose of buying a battery with 800 or 1000 CCA.

From the looks of it these units all work in the same manner they handle a range of source power and manage the battery status on the other side.

The CTEK does nothing on the engine side. It just charges the aux side. With the SmartPass add-on, it will monitor the aux side and can use power from there to also charge the engine side, for instance from the solar or from shore power connected to the aux side.

 

[dwh]

Ok interesting read
From what I can tell amps pushed to the battery as a general rule you want 25% or less of the batteries amp hour rating or you can cook it given it cant absorbe the amperage ie charge fast enough.

Yea, that's usually expressed as a percentage of the battery capacity (C). So if it's limited to 25%, that would be C/4 or C*.25.

That used to be what pretty much all battery manufacturers recommended, and it's still a nice safe number for just about any battery.

But AGMs generally don't have that same limit. Some few manufacturers do still use that number, but most have updated to something more realistic.

A few are totally not even close to the "25% rule of thumb" - Odyssey specs C*4 (400 amps charge to a 100ah battery) as max, and their recommended MINIMUM is C*.4 (40 amps for a 100ah battery). Lifeline and Optima AGMs have no max limit as long as they don't overheat.

This also is dependant on the battery type and its quality etc. So it sounds like for the most part you cant just dump a big amperage on the battery.

Well the battery itself will limit the amperage by its internal resistance. So even if you had a 100a alternator, there might only be 5 or 10 amps flowing through the battery.

It's not an issue with a constant voltage charger (like a voltage regulated alternator), but it can be an issue with a constant current charger that will raise its output voltage potential to try to pump its full rated amps through the charging circuit.

 

[calicamper]

Interesting
Flow control essentially from the two sides and the smart pass lets you flow power back across to the vehicle side if needed.

 

[dwh]

It takes a LOT of reading to get to to a real description of what the SmartPass (http://smartercharger.com/products/dcdc/ctek-smartpass/) actually does, but basically, it is an intelligent relay (like the Blue Sea ACR) but engineered to work with the D250S B2B. Basically, when you start the engine, it closes the relay to put the batteries in parallel. When the bulk stage is complete, that is, when the charge rate drops to about 20A, then it opens the relay and completes the absorb stage using the D250S alone. As noted, the D250S doubles as a solar controller.

dwh has mentioned the caveats of size and cost. But if your alternator doesn't charge above 14v, this might be a slick solution.

The SmartPass also enables bi-directional charging, and includes a low-voltage disconnect (LVD) to supply loads without worrying about taking the battery voltage too low.

 

[crusaderJK]

Dust
I'm building a similar set up. But no ARB. I think you only need an 80 watt panel from your description, but you go bigger on the Amp Hours stored ie larger battery. In my thread it was pointed out the ARB draw is basically 2amps per hour. One poster noted he was running his arb on a 75ah marine battery and had a 80watt solar panel, he noted full sun the 80 watt does about 4amps and in cloudy conditions 1amp conservatively etc. The 75ah battery will run the 2ah arb 3 days with no added juice.

That poster was me.
I should add, that the 2Ah/h were given by another poster and this number would be for a large fridge (65qt) and deep-freezing stuff down to 5°F at an ambient temperature of 90°F.
My fridge is a small Waeco (35qt) and it draws about 0.8Ah/h - just cooling, not freezing.
Here's a link to the waeco coolers with all the specs.

I like the LCD readout on the steca ($140)

But, point taken.

Yup, the Steca is nice, but there are cheap clones that also have the LCD display. (Edit: dang pleonasm...)

 

[calicamper]

Looks identical to mine

 

[crusaderJK]

That's one of the clones.
When I was looking around for parts for my solar setup, I didn't want to pay the price for the Steca either.
But then I found a good package deal and paid around $350 (+ taxes) for an 80W panel, 75Ah gel battery, the Steca and the cables. Steca and cables are made in Germany, panel and battery in China.

I think as long as you don't really depend on the parts or wanna fit your house with kW of solar panels, you can cheap out and buy the chinese stuff.

 

[dwh]

http://www.alibaba.com/product-detail/LCD-LED-solar-charge-controller-12V_1470118141.html

 

[Dust999]

Just to close off this thread.

I've decided to go with the trojan 31agm battery, the ctek dc to dc dual charger, 2x100w renogy solar panels and the arb 50qrt fridge.....which arrived yesterday.....but throws an error message....so it has to go back.........

 

[southpier]

why is everyone using asterisks and no footnotes? this is confusing as fark.

 

[dwh]

why is everyone using asterisks and no footnotes? this is confusing as fark.

<waves hand>"This is not the multiplication symbol that you are looking for."

 

[V85562A]

Just to close off this thread.

I've decided to go with the trojan 31agm battery, the ctek dc to dc dual charger, 2x100w renogy solar panels and the arb 50qrt fridge.....which arrived yesterday.....but throws an error message....so it has to go back.........

Really interested to see how this works out for you. I want to do a similar setup but separate MPPT CC, 2 x 6V GC2 220ah batteries and trying to figure out the best way to connect to the starting battery/alternator.

My guess is this won't impact battery drainage on heavy loads? Coffeeboxx that pulls 1500watts will still pull mostly from the batteries and get slowly recharged?

 

[coolfeet]

I also want to install the Blue Sea 7610. I am not experienced in auto electric. Can a novice do this? I am using a sealed agm inside my van.


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[coolfeet]

@crusader jk. Where did you buy your solar kit?


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[AndrewP]

I also want to install the Blue Sea 7610. I am not experienced in auto electric. Can a novice do this? I am using a sealed agm inside my van.

It's only 3 connections to the 7610 itself. You will need to run fairly big wires across your firewall, so you'll need properly sized fuses to protect the wire.