RUNNING 12V DIRECTLY FROM ARRAY

nasty

Hello

Did a search but I'm not sure I'm asking the question correctly. I have 4 Kyocera 140w panels that charge a battery bank about 75' away. 12v system connected with buried 4/0 cable to the CC and batteries. I need to operate a 12v pump for a shower house that is about 15' away from array. Instead of running wire 75' from the batteries to the pump can I just connect directly to the array so there isn't as much line loss or would that be negligible? Thanks for any help.

mcgivor

A DC-DC isolator converter can convert 9 to 18V to a stable 12.5V, available in various capacities, Samlex has them and possibly other manufacturers. You don't want to overvoltage the pump.

BB.

Do you have more information on the pump specifications (amps, volts, watts, max voltage, etc.)?

-Bill

Estragon

There are pumps that can be run directly from panels but they tend to be expensive.

nasty

I have a Shurflo 2088. 12V 3.5GPM 5.8-9.1 Amps

mike95490

mcgivor said:

A DC-DC isolator converter can convert 9 to 18V to a stable 12.5V, available in various capacities, Samlex has them and possibly other manufacturers. You don't want to overvoltage the pump.

I think that is a mistake .   A common DC-DC convertor cannot manage the complex MPPT tracking that PV panels require.  Pull too much and the  panel voltage collapses.  And it will foul up the downstream charge controller

BB.

It sounds like you should use a Linear Current Regulator if you want to avoid the batteries (good idea if this work for you):

https://www.solar-electric.com/7amplincurbo.html

-Bill

mcgivor

mike95490 said:

mcgivor said:

A DC-DC isolator converter can convert 9 to 18V to a stable 12.5V, available in various capacities, Samlex has them and possibly other manufacturers. You don't want to overvoltage the pump.

I think that is a mistake .   A common DC-DC convertor cannot manage the complex MPPT tracking that PV panels require.  Pull too much and the  panel voltage collapses.  And it will foul up the downstream charge controller

Not exatly sure what is meant by the panels needing complex MPPT tracking, unless you were referring to the controller used down stream, I asumed it was not MPPT as the array is 12V and the use of #4 /0 conductors  , if it were a simple PWM perhaps it would be of less concern as it would simply be a volt drop and a PWM CC would just compensate, as it would when a cloud passes. If you were referring to a MPPT CC  your rationale makes sence. Just ideas for solutions.

bill von novak

mcgivor said:

Not exatly sure what is meant by the panels needing complex MPPT tracking, unless you were referring to the controller used down stream, I asumed it was not MPPT as the array is 12V and the use of #4 /0 conductors  , if it were a simple PWM perhaps it would be of less concern as it would simply be a volt drop and a PWM CC would just compensate, as it would when a cloud passes. If you were referring to a MPPT CC  your rationale makes sence. Just ideas for solutions.

The problem is that the DC/DC will pull as much current as it needs to continue to power the load.  When that power is not available (sun goes behind the cloud) it will pull the voltage down as low as it can and keep it there.  When the sun comes back, the DC/DC will still be pulling maximum amps at (for example) 5 volts and you will have very little power available.

PWM is on/off.  If you connect it to your pump it may not like it since it will be slamming on and off all the time.  (Equivalent to you turning the pump on and off rapidly, 60 times a minute or so.)

As BB mentioned, LCB's (current boosters) are designed to do exactly this - power a pump directly from a solar panel.

mcgivor

bill von novak said:

mcgivor said:

Not exatly sure what is meant by the panels needing complex MPPT tracking, unless you were referring to the controller used down stream, I asumed it was not MPPT as the array is 12V and the use of #4 /0 conductors  , if it were a simple PWM perhaps it would be of less concern as it would simply be a volt drop and a PWM CC would just compensate, as it would when a cloud passes. If you were referring to a MPPT CC  your rationale makes sence. Just ideas for solutions.

The problem is that the DC/DC will pull as much current as it needs to continue to power the load.  When that power is not available (sun goes behind the cloud) it will pull the voltage down as low as it can and keep it there.  When the sun comes back, the DC/DC will still be pulling maximum amps at (for example) 5 volts and you will have very little power available.

PWM is on/off.  If you connect it to your pump it may not like it since it will be slamming on and off all the time.  (Equivalent to you turning the pump on and off rapidly, 60 times a minute or so.)

As BB mentioned, LCB's (current boosters) are designed to do exactly this - power a pump directly from a solar panel.

I think you missed my point, nevertheless BB's suggestion may be better for the application, never suggested drive the pump with PWM. What I was trying to say is if the array is 12V and you tap off that 12V at the array, the PWM CC down stream would not care that there is a volt drop. If however you were to tap off one 12V panel in a string feeding a MPPT CC down stream, that would cause problems, was just trying to clarify what @mike95490 was attempting to explain.

nasty

I am starting to think running a large enough cable from my 12v distribution center 75' away to the pump might be the way to go. Need to see how big of wire it will take to minimize line loss. That way we can shower when there is no sun. Thanks for all the help.

mike95490

The array is NOT 12V.   It is an 18V array for charging a 12V battery.   Wire a pump directly to an 18V panel and you will be buying a lot of pumps.   Trying to wire a 18-12V DC-DC will not work, at some point in the day (like when the PWM charger first kicks on and effectively drops the panel voltage to 12V) it will collapse the Panel voltage and no more pumping that day,

As BB said, an LCB is the tool to use.  But I have no idea how well it will work wired in parallel with a PWM controller. My guess is poorly.

 A 12V Vmp array is good for charging a 6 or 8 V battery,   Panel voltage HAS to be larger than battery voltage in order to "Push Amps" into the batteries at a reasonable rate.

mcgivor

Understood, should perhaps have said, 12V nominal array, just thought it unnecessary. By the way your signature says you have a 12v array, do you charge a 6v or 8v battery with that? Not serious of course.
 mike95490 said:

The array is NOT 12V.   It is an 18V array for charging a 12V battery.   Wire a pump directly to an 18V panel and you will be buying a lot of pumps.   Trying to wire a 18-12V DC-DC will not work, at some point in the day (like when the PWM charger first kicks on and effectively drops the panel voltage to 12V) it will collapse the Panel voltage and no more pumping that day,

As BB said, an LCB is the tool to use.  But I have no idea how well it will work wired in parallel with a PWM controller. My guess is poorly.

 A 12V Vmp array is good for charging a 6 or 8 V battery,   Panel voltage HAS to be larger than battery voltage in order to "Push Amps" into the batteries at a reasonable rate.

 anyhow, think @nasty has come up with the best solution, run the pump from the battery.

mcgivor

nasty said:

I am starting to think running a large enough cable from my 12v distribution center 75' away to the pump might be the way to go. Need to see how big of wire it will take to minimize line loss. That way we can shower when there is no sun. Thanks for all the help.

To stay within 3% volt drop, #2 AWG  will allow 67 feet, 15A  at 12V  FWIW. 

Tricksailing

nasty said:

I am starting to think running a large enough cable from my 12v distribution center 75' away to the pump might be the way to go. Need to see how big of wire it will take to minimize line loss. That way we can shower when there is no sun. Thanks for all the help.

Not a question of minimizing line loss - just a question of supplying enough power to run your pump. I'm pretty sure the Shurflo will run on 11 volts (you can test it), in which case a 10% voltage drop is acceptable (but consider cable heating) and cabling much cheaper.  Based on https://www.solar-electric.com/wire-loss-tables.html #6 should be fine.
Depending on your water source location and heating method, it may be cost effective to locate the pump near the batteries and run water lines to the shower.

jonr

There are many 12V diaphragm pumps in the 8A range.  Even 8 gauge is fine.

nasty

I was thinking of using 6 gauge wire. Pump is at 250 gallon water tank and pumps up 2-3' to on demand water heater.

just starting

That pump uses so little power I would get a small agm like 35-50 amps and a 80 watt panel with a ms sunguard 4.5 amp cc it would compare to the #6 price . I used a setup like that for a few years it for a few years. I doubt you will pump for more than an hour or two a day.