12V load on a 48V system

awade

I learned so much from reading this forum but I finally had to join because I've had this burning question that I can't seem to resolve. Thanks in advance for any answers you can offer.

I have a 48V system with sixteen 415ah L16's an Outback inverter and charge controller. I've tried various water pumps of various voltages and currents over the years and they all seem to fail relatively quickly. The work horse pumps that I've found to be the most reliable over time are the small 12V RV pumps like the Shurflo 2088-422-444 (3.5A at 12V). Problem is, how to use the pump with the system.

For the last year, as an experiment, I wired the pump direct to two of the 6V batteries within the 48V configuration, thus pulling 12V. It's been working perfectly, perhaps because of the low amperage, and those two batteries don't seem any worse off than the others. In fact, when all loads and charges are off, they seem to have slightly higher state of charge.

That said, I've read and heard that you should never wire a 12V load directly into a 48V battery bank so I am searching for a solution.
Short of setting up a standalone 12V system just for a single pump, I've considered using 48VDC to 12VDC converter made for golf carts but I don't know how efficient they are.
Samlex makes a 48V to 12V converter that is more expensive but may be more efficient, or maybe not. I found it here: http://www.iloveitsolar.com/catalog/i412.html
Also, someone recommended using the Morningstar Sunsaver 15A MPPT as a 48V-12V converter since it can handled higher input but that sounds like overkill.
Early on, I had a 12V charger running off the AC inverter, which was servicing a 12V battery for the pump. It worked but 48VDC to 120AC to 12VDC to seemed ridiculous. Or is it?

Any elegant solutions out there? Your insights would be greatly appreciated.

Thanks!

Cariboocoot

Re: 12V load on a 48V system

Welcome to the forum.

Using a separate 12 Volt system recharged from the 48 might be electrically inefficient as you say, but it can be a lot more practical in terms of expense than buying a converter.

Drawing off one section of the 48 Volt bank, even with a small drain, will imbalance the system. This will not show up right away, but instead will manifest itself as the batteries with extra use failing before the others.

You might even just get a whole separate small system to support the pump, as it probably would not need a large battery and associated panel & controller.

awade

Re: 12V load on a 48V system

Thanks for your quick response Cariboocoot,

Are you suggesting that the Sunsaver controller option is viable as a way to balance the 12V load over the 48V battery bank? If so, would I need a separate 12V battery between the controller and the pump or can I connect the pump directly to the controller without a battery.

Seems that even a charge controller or a converter would still be less expensive than setting up a new 12V system from scratch.

niel

Re: 12V load on a 48V system

using the 120vac inverted power to operate a 3 stage charger to a dedicated 12v battery may be one way and would keep the main battery bank operating in balance. the 48v-12v converter is far more efficient and skips wasteful steps and costs far less than all of the components needed for a dedicated battery with ac charger from an inverter. sometimes people have some of the components to enable the first method, but the dc to dc converter is best imho.

awade

Re: 12V load on a 48V system

Hi Niel,

Yeah, finding the most efficient converter might be best. Hopefully less maintenance than a separate system too. I've got about as much as I can handle, and I'm hoping to find a solid, long term solution.
I wonder, if my total 12V load is 3.5 amps, would it be more efficient to go with a small 5-10 amp converter or will a larger unit provide more efficiency through less resistance or better heat management, or just better durability?

Cariboocoot

Re: 12V load on a 48V system

awade wrote: »

Thanks for your quick response Cariboocoot,

Are you suggesting that the Sunsaver controller option is viable as a way to balance the 12V load over the 48V battery bank? If so, would I need a separate 12V battery between the controller and the pump or can I connect the pump directly to the controller without a battery.

Seems that even a charge controller or a converter would still be less expensive than setting up a new 12V system from scratch.

Absolutely must have a separate 12 Volt battery.
But considering the price of the MS 15 MPPT, using a small PWM charge controller and its own panel may be a more cost-effective option. It depends on how much pump power you need and what kind of bargains you can find.

vtmaps

Re: 12V load on a 48V system

Are you aware that shurflo makes the 2088 series pump in other voltages, including 120 V AC? --vtMaps

awade

Re: 12V load on a 48V system

Hi vtmaps,

Thanks for the thought. Yeah I am aware of the 120V AC version of the shurflo pump and have tried them twice. I wish I could say I had a good experience but both started running down, over heating or yielding less pressure after about 6-9 months of regular use. Not sure why but the 12V version has been providing solid service in both our house and our greenhouse with no signs of overheating and providing excellent pressure despite pushing through multiple stages of filtration. The greenhouse 12V pump has been working daily for 4 years with no signs of trouble. It's been running on an old truck battery tied to a 20 watt panel. Still going strong, knock on wood.

awade

Re: 12V load on a 48V system

I found a $20 48V to 12V converter and it's working great so far. Thanks for the input.

2manytoyz

Re: 12V load on a 48V system

Sounds like he's already found a converter, but others might find this info useful.

I bought a 25 Amp 48V to 12V DC-DC converter (commonly called a reducer) for $45. Works great. Pics and details of my testing here: http://www.buggiesgonewild.com/electric-ezgo/70417-48v-dc-dc-converter.html