Looking For 12v Regulator
SpiderMan
Registered Users Posts: 11 ✭✭
I have a conflict in our RV between the solar charge controller and a furnace. The Propex furnace goes into an error mode if it senses input voltage above 15v. Unlike some furnaces, the thermostat on the Propex is not a simple mechanical switch which interrupts power, so high voltage is a problem even when the thermostat is in the OFF position. During warm weather (when I don't need the furnace) this isn't a problem since I've got the absorption voltage for our flooded batteries set at 14.6v. But our coach batteries are exposed to the weather with a battery temperature sensor. Thus, in cold weather the charge controller pushes voltage well above what the furnace will tolerate. My only solution so far has been to reduce the maximum voltage output of the solar controller (Blue Sky 2512iX w/ ProRemote). That keeps the both furnace and the wife happy, but leaves the batteries undercharged.
Nothing else in the RV is affected by this problem - only the Propex furnace. I'm looking for a device that will limit voltage supplied to the furnace to about 12 or 13v. It doesn't need to boost low voltage, but simply to "clip" high voltage. Operating load is under 2 amps (the furnace is rated at 1.7 amp, but I've never seen it actually draw more than about 1.3 or so). The device needs to be able to limit the voltage even when no current is being drawn because the furnace will go into an error mode even if it senses high voltage when not running or turned off.
The furnace distributor (not manufacturer) has suggested the following gizmo, but unfortunately the sales page contains mostly hype with few details. Any thoughts?
I've also heard about putting a diode in series with the load to reduce voltage, but it's not clear to me if a diode would limit the voltage when there's no current flowing.
Comments
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
- Input Voltage: DC 6V - 20 V
- Output Voltage: DC 12V
- Output Current: 12A (Max)
- Output Power: 144 W (Enough Power)
- Conversion Efficiency: Up to 93%
These are exactly the specifications you need for your "gizmo".What else do you need to know?
And no a Diode is not a good solution.
There is another unit (same picture, higher specs) that appears to have reasonable reviews--Although there were a few failures.
Just make sure you keep the wires short/heavy and connect them correctly (input connected with correct polarity/voltage, output not connected to battery instead, etc.).
And in this case, find out if the furnace support folks actually have used this unit, or just supplied a link to a product that could work.
-Bill
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
I looked for a good primer on understanding DC to DC converters, but I was not very successful. DC converters are a complex subject with many different implementations (circuit types) and also involved some pretty high level math (control theory). Here is a relatively complete PDF paper that may help (skip over the math and pay attention to current flow diagrams):
https://www.eecs.umich.edu/courses/eecs373/readings/dc-dc-primer.pdf
The issue is that there are "buck" or take high voltage and down converter to low voltage. "Boost" converters which take low voltage and make a higher voltage. And "Buck-Boost" converters that take a wide range of input voltages and make a stable output voltage (both buck and boost function in one regulator).
To a degree--Just like we "accept" that AC transformers work. You can treat DC to DC converters sort of like a "DC Transformer" or "Black Box". If your application is within the abilities of the converter, they work.
The basic idea is that you have a switch (transistor) that controls current flow to an inductor. Then usually through a blocking diode and filtered with a capacitor. The inductor/coil stores energy and allows energy to be "converted" from one (from high voltage/low current or low voltage to high current--more or less like an AC transformer) to another voltage.
With switch mode power supplies, they are more efficient than "linear" regulators (for down regulating--Think of opening/closing a water valve to regulate water pressure). And linear regulators cannot "boost" voltage. The inductor can increase voltage in a boost circuit (think of "charging an inductor" by getting current flowing, then you cut the current--And the you get high voltage across the inverter, or even a spark, as the inductor tries to keep the current flowing--That current flow is directed through a blocking diode to a higher voltage output+filter capacitor).
The key component is the inductor and its ability to store energy.
-Bill
Would a unit closer to my power needs be more efficient, especially related to standby losses with no load? Such as This One? It's also a tad less expensive and actually has reviews (all of which are positive). Due to the transient nature of furnace use, it's off far more than on. Or are these power losses so low that I shouldn't worry about them. Neither unit lists numbers for standby losses. The furnace itself is rated at 0.01 Amps on standby.
The furnace manual makes no mention of grounding its metal casing, which is mounted to the bottom of the wood floor of the RV. It's quite possible that there is a grounding path through the gas supply line or through inadvertent metal-metal connections on shielding I've installed around the furnace touching the vehicle chassis.
Yes, you are correct that you do not want too large of converter--They do have idling current and a smaller unit, should have less idle draw. However, without measuring, I could only guess (something like 1-2% of the rated current??? i.e., 12 amp unit could draw as much as 0.12 to 0.24 amps on standby--Not trivial). You will want a manual on/off switch for when the furnace is not needed to kill standby power.
Grounding the case is always a good idea (just use a green wire back to a good ground point). The case is probably isolated, but things can go wrong.
-Bill
I just measured and sure enough a significant portion of the current (about 2/3) is returning on the ground path rather than through the negative wire. I've ordered the voltage regulator and will find out by experiment if the ground path current is an issue or not.
Thanks to all for your responses. I'll try to remember to post a follow-up once I've got the regulator installed.
Many folks find out that high voltage difficulty when they go into cold climates (and Canada, etc.). 16-17 volts is within the "nominal" cold battery (near/below freezing) charging voltage range. You can find AC inverters that will run at this "elevated voltages" if you look around hard enough. And one reason I suggest running efficient 120 VAC appliances than trying to run everything off of 12 VDC (electronics, lighting, etc.).
The issue with ground paths through chassis/sheet metal is common for vehicles. Many devices won't care (just ground the device to a good ground/negative battery bus with tie to a good local chassis ground). Hopefully, you are connect that the DC converter will not care either (they can be designed either way).
Please let us know how it works out for you.
-Bill
Thanks again to all for your input.