How to make a cheap isolated dual-battery setup for $50

[dwh]

So a friend of mine that owns a boat, and a Jeep, and about everything else you could imagine, asked why no alternator regulator. As I have no idea, all I can do is post the link to the product and hope those more knowledgeable will chime in. His quote follows, "Right now your alternator puts out a one-stage charge suitable for a flooded battery. If you use AGM or Optima batteries, especially on that is to serve as a house battery, you ideally want a three-stage charge. You batteries will charge at least twice as fast and will live much longer lives. Speed of charge, particularly from a deep discharge, is something that would appeal to me in an overlanding scenario."

http://www.xantrex.com/power-products/power-accessories/alternator-regulator.aspx

Thoughts?

Probably beyond the scope of this thread.

But a few thoughts...

You have a modern vehicle. Probably already has a fairly smart voltage control system managed by the galactic central computer core known as "Deep Thought". In other words, if the voltage regulator is part of the PCM - good luck fitting an aftermarket unit.

"One-stage" charging is known as "constant voltage". Multi-stage combines an initial "constant current" bulk stage, then a constant voltage absorb stage. Once the charging is done, then it reduces voltage and maintains at a constant voltage "float" stage. So yea, a multi-stage will get the bulk stage done sooner. That's nice because you don't have to wait 12 hours for the battery to reach full - now it might only take 8 hours... In other words, the benefit may not be enough to really make a difference.

Also a single stage - one long absorb at say 14.5v might get the job done in around the same total amount of time as a quick bulk up to 14.5v then a long absorb at a reduced voltage of say 14.2v. Again...might not help much.

But sure - multi-stage w/temperature compensation is certainly, "the proper way". It's really just a question if it's worth doing it. Big bank of expensive batteries? Hell yea. One aux battery on a weekender trailer? Might not be worth it.

Another way to go - DC-DC charger that steps up the constant voltage input from the chassis bus and uses it to do a multi-stage on the aux. There's a bunch of those. CTEK and Sterling are pretty common, but they don't put out as many potential "max amps":

http://www.ctek.com/lu/en/chargers/D250S DUAL

http://www.sterling-power-usa.com/


The Sterling site will show you a whole lot of the various ways that battery charging can be done. Different strokes for different situations.

 

[Phoenix]

Cool. Thanks for the explanation. Much appreciated. I finally found out what the thing costs. Definately outside the scope of this thread.

 

[DiploStrat]

Having spent a lot of time and money installing and dismounting a form of alternator/regulator, I suggest you spend some time reading this link: http://www.smartgauge.co.uk/controllers.html You may also enjoy some of the "discussions" that dwh and I have had of voltages.Finally, get a voltmeter and test your voltages; the odds are good that they are high enough and that, if you have a modern vehicle, you already have a multi stage charger. The biggest issue that you are likely to face is undersized cables.

 

[Shoeman]

Deep Thought. I laughed at that one. Know where did I put my towel??

 

[dwh]

Deep Thought. I laughed at that one. Know where did I put my towel??

42.

 

[DiploStrat]

42? That explains a lot!

 

[Dan Grec]

Hi All,

I love this thread! - I'm ordering parts now to build my solar-equipped setup.

I have a question on wiring the loads with regards to the Charge Controller.

Looking at the Wiring section of the Morningstar SunSaving Operators Manual It says to wire the "load" into the controller.

I.e. lights, pumps, motors and electrical devices.

So I'm wondering if I should wire them all off the "load" section of the charge controller, or if I just wire them up to the secondary (isolated) battery?

I'm looking at the SS-20L-12V - which says maximum load current of 20A - which should cover my needs, if I were to wire everything up to the controller.

I'm wondering what the difference is when the sun is shining and I have a load (I.e. fridge comes on) - if I wire to the controller, will the controller shunt the power from the solar straight to the fridge and not involve the battery?

And if I wire all the loads onto the battery, will the controller shunt the power into the battery, then the fridge will pull the power out of the battery?

or will the end result be the same thing, and it makes no difference either way?

Thanks,
-Dan

 

[calicamper]

So a friend of mine that owns a boat, and a Jeep, and about everything else you could imagine, asked why no alternator regulator. As I have no idea, all I can do is post the link to the product and hope those more knowledgeable will chime in. His quote follows, "Right now your alternator puts out a one-stage charge suitable for a flooded battery. If you use AGM or Optima batteries, especially on that is to serve as a house battery, you ideally want a three-stage charge. You batteries will charge at least twice as fast and will live much longer lives. Speed of charge, particularly from a deep discharge, is something that would appeal to me in an overlanding scenario."

http://www.xantrex.com/power-products/power-accessories/alternator-regulator.aspx

Thoughts?

Exactly why I stuck with old school flooded on our boat. AGM'S need more advanced power system and I didnt need to spend any more on upgrades. Lead acid batteries are also more tolerant of abuse regarding random use and charge cycles.

 

[calicamper]

Hi All,

I love this thread! - I'm ordering parts now to build my solar-equipped setup.

I have a question on wiring the loads with regards to the Charge Controller.

Looking at the Wiring section of the Morningstar SunSaving Operators Manual It says to wire the "load" into the controller.

I.e. lights, pumps, motors and electrical devices.

So I'm wondering if I should wire them all off the "load" section of the charge controller, or if I just wire them up to the secondary (isolated) battery?

I'm looking at the SS-20L-12V - which says maximum load current of 20A - which should cover my needs, if I were to wire everything up to the controller.

I'm wondering what the difference is when the sun is shining and I have a load (I.e. fridge comes on) - if I wire to the controller, will the controller shunt the power from the solar straight to the fridge and not involve the battery?

And if I wire all the loads onto the battery, will the controller shunt the power into the battery, then the fridge will pull the power out of the battery?

or will the end result be the same thing, and it makes no difference either way?

Thanks,
-Dan

Dan I'm doing the same type of project right now. The advantage of routing through the controller is it will cut power when you hit 11volts preventing battery damage. As for power, its just power in and power out with the load side of the controller being a watch dog making sure you dont kill the battery by going below 11volts.

 

[crusaderJK]

I'm wondering what the difference is when the sun is shining and I have a load (I.e. fridge comes on) - if I wire to the controller, will the controller shunt the power from the solar straight to the fridge and not involve the battery?

Dan I'm doing the same type of project right now. The advantage of routing through the controller is it will cut power when you hit 11volts preventing battery damage. As for power, its just power in and power out with the load side of the controller being a watch dog making sure you dont kill the battery by going below 11volts.

Like calicamper said, wiring through the controller will give you low voltage protection. If you don't need that you can go either way.

I have my loads wired to the battery since my fridge has low voltage protection as well, and my other loads (cell and GPS charger) don't really affect the battery that much.
Anyway, I'm still thinking of connecting my loads to the controller, because it'll also provide info about the current draw and Ah consumed.

 

[DiploStrat]

Exactly why I stuck with old school flooded on our boat. AGM'S need more advanced power system and I didnt need to spend any more on upgrades. Lead acid batteries are also more tolerant of abuse regarding random use and charge cycles.

I'm not sure I would agree with those statements. You may wish to compare the Trojan and Lifeline battery manuals:

Trojan: http://www.trojanbattery.com/pdf/TRJN0109_UsersGuide.pdf

Lifeline: http://www.lifelinebatteries.com/manual.pdf

The voltages differ, but the stages are the same.

An open cell battery can recover from mild overcharge by adding water and they are less expensive. AGMs will take more current and offer the option of being mounted on their sides.

 

[Dan Grec]

Like calicamper said, wiring through the controller will give you low voltage protection. If you don't need that you can go either way.

Thanks for the reply (and calicamper).

The battery I'm using - Optima Yellow Top - has a low voltage cut off at 10.5v to protect itself. Does that mean I don't really need to use the load on the Charge Controller because the battery will take care of itself anyway?

Thanks,
-Dan

 

[dwh]

The battery I'm using - Optima Yellow Top - has a low voltage cut off at 10.5v to protect itself.

You should double-check that...that doesn't sound right. I'm looking at the specs right now, and I don't see anything that says that:

http://d26maze4pb6to3.cloudfront.net/optimabatteries/4713/4583/5068/YELLOWTOP_Full_Specs_Sheet.pdf

It does say "assuming 100% discharge - 10.5 volts" - but all that means is that when it gets down to 10.5v it is "technically considered dead". That's the same rule of thumb for all "12v" automotive batteries.

But that doesn't mean it's truly dead, or that it won't go lower - it certainly can and will go lower. Because Optimas have a low internal resistance, it's actually easier to take them lower than it would be for a different battery. Optima used to have a video showing the recovery procedure to recharge a battery that has gone so far below 10.5v that a normal charger will refuse to charge it. I don't see it now, but it might still be on YouGoogleTube.

Does that mean I don't really need to use the load on the Charge Controller because the battery will take care of itself anyway?

If you're running your battery down that far on a regular basis, then you need more battery. I wouldn't worry about the low-voltage disconnect. Sure, use the charge controller's LVD if you want and your loads are under 20a, but really, you shouldn't be draining your battery down to 11v regularly.

And you answer your earlier question: The solar charges the battery. The load connection on the solar charge controller drains from the battery. Dead simple. There is no "shunting" power around from this side to that side and whatnot.

So if the sun is shining and say there is 20a coming off the solar panel to the battery, and your loads are sucking 5a - there will be 15 left over to flow to the battery.

 

[Dan Grec]

Thanks for the info dwh, it's extremely helpful.

You should double-check that...that doesn't sound right. I'm looking at the specs right now, and I don't see anything that says that:

Check this out:
http://d26maze4pb6to3.cloudfront.net/optimabatteries/4713/4583/5068/YELLOWTOP_Full_Specs_Sheet.pdf
Page 5 (for the D34 - the exact ones I'm getting)

It says
"Reserve Capacity: BCI: 120 minutes (25 amp discharge, 80°F (26.7°C), to 10.5 volts cut-off)"

So I was assuming that means the battery will cut-off at 10.5v to protect itself.

If you're running your battery down that far on a regular basis, then you need more battery. I wouldn't worry about the low-voltage disconnect. Sure, use the charge controller's LVD if you want and your loads are under 20a, but really, you shouldn't be draining your battery down to 11v regularly.

Thanks, that's good to know. I don't want to run it down to 11v regularly, but I'm just going to not start the engine for as many days as possible... so chances are I will entirely drain the battery from time to time if I go too many days without running the engine.
It sounds like I should at least use the LVD of the controller, as 11v is better than 10.5v (but still not good). And I should watch the voltage over the days to see how it goes, and for how long my solar will keep up with my loads.

And you answer your earlier question: The solar charges the battery. The load connection on the solar charge controller drains from the battery. Dead simple. There is no "shunting" power around from this side to that side and whatnot.
So if the sun is shining and say there is 20a coming off the solar panel to the battery, and your loads are sucking 5a - there will be 15 left over to flow to the battery.

Thanks, that makes sense.

Based on all of that, and given that my load will always be less than 20A, it sounds like I should use the "load" of the controller, and not just wire directly to the battery.

Thanks again!
-Dan

 

[dlichterman]

Based on all of that, and given that my load will always be less than 20A, it sounds like I should use the "load" of the controller, and not just wire directly to the battery.

Since you said there will be multiple loads connected - you are going to need some sort of distribution block. Depending on your charge controller it may be difficult to use a large enough wire gauge with the controller - this is why I opted to use blue sea fuse blocks connected directly to the battery with 4AWG since this makes adding a circuit a lot simpler, and each one is fused.