[RE-wrenches] combining 24v and 12v systems

[Allan Sindelar]

Agreed: no 12v tap. I’ll add (with modest experience, as this doesn’t come up as an upgrade very often any more) that Mean Well, despite the odd name, proved itself pretty reliable in some early Wattsun tracker drives and some other DC-DC applications. Available online; see https://www.meanwell-web.com/en-gb/dcdc-converters/
Allan

> On Dec 31, 2019, at 10:46 AM, Dan Fink <danbob88 at gmail.com> wrote:
> 
> I second everyone. Center-tapping a 24 or 48v battery bank for 12v SEEMS like it should work just fine, especially for low load infrequent use like a 12v water pressure pump for a greenhouse, a weather station, etc.. Nope, I've been a loser every time, with that battery or pair always the first to go bad.
> 
> Samlex and Victron both make DC-DC converters I have had good luck with; they are thermally protected and you can stack multiple units for more amperage.
> 
> Dan Fink
> Executive Director, Buckville Energy Consulting
> NABCEP PV Associate
> NABCEP Certified PV System Inspector
> IREC Certified Instructor™ for: 
> ~ PV Installation Professional
> ~ Small Wind Installer
> NABCEP Registered Continuing Education Providers
> danbob88 at gmail.com
> 970-672-4342
> 
>  
> 
> 
>> On Tue, Dec 31, 2019 at 10:57 AM Ray <ray at solarray.com> wrote:
>> Even with battery balancers, battery tapping is still a really bad idea.  I know, I did it on my own system in the 90s.  The DC/DC converters are the way to go, but be sure and over size it by a fair amount to handle the fridge starting surge.  Unfortunately my favorites are no longer available: made by Solar Converters in Canada. I've seen them last decades.  Iota should be good stuff, their chargers have long term reliability.  Samlex inverters have been around for quite a while too, but I don't have long term experience with their converters.  
>> 
>> Ray Walters
>> Remote Solar
>> 303 505-8760
>>> On 12/31/19 10:05 AM, Dave Angelini Offgrid Solar wrote:
>>> Tapping a battery bank is not a good practice. it will unbalance the bank. Much better to add a 24V electronic converter for the 12V loads. Then replace the 12V loads when time permits. They will need a spare converter so buy 2. Amazon has tons of these converters. Your quote is great BTW. H N Y !
>>> 
>>>  
>>> Dave Angelini Offgrid Solar
>>> "we go where powerlines don't"
>>> http://members.sti.net/offgridsolar/
>>> e-mail  offgridsolar at sti.net
>>> text 209 813 0060
>>>> On Tue, 31 Dec 2019 11:52:20 -0500, Chris Schaefer <chris at solarandwindfx.com> wrote:
>>>> 
>>>> G'day and Happy New Year to All,
>>>>  
>>>> Recently came across this offgrid OB FX system. The first part is a 12v battery system w/ 2 PV modules, 2 Trojan L16  batteries used to power a frig and freezer about 6 years old. The second is a 24v with 3kw of PV, 4 Trojan L16's, twin OB FX inverters installed by an HVAC contractor back in 2016. This was their first offgrid project. Oh boy, lol. The client would like to add more battery capacity to both. My thought here is since we are powering only a 12v frig and freezer why not simplify the system by creating a single battery bank and then tapping off of the 24v bank using proper fusing and creating a 12v buss? Admittedly I live in a 48v world so I'm asking our esteemed colleges as to options on how to address this. 
>>>>  
>>>> Oh yeah, the installer is unresponsive (no surprise there) and they are also having firmware issues with an old Mate 3 and would like me to install a new Mate 3s but that's another issue I'll tackle when I head out to site. 
>>>>  
>>>> Thanks All,
>>>> Christopher- 
>>>> Chris Schaefer's
>>>> 
>>>> Tel/Fax 585-229-2083 or Cell 585-748-1870 
>>>> 5115 South Hill Road ~ Canandaigua New York 14424
>>>> www.solarandwindfx.com ~ E-mail: chris at solarandwindfx.com
>>>> 
>>>> 
>>>> 
>>>> Thomas Jefferson, the author of our great Constitution, once said, "democracy" will cease to exist when you take away from those who are willing to work and give to those who would not."
>>>> 
>>> -- 
>>>  
>>> 
>>> 
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