Dave in AZ
Well-known member
This thread is turning into an enjoyable engineering-fest 
DC-DC charger as an alternative to generator?
- Thread starter Martinjmpr
- Start date
crazysccrmd
Observer
They don’t though. It is not possible to cool through natural means below the ambient air temperature. If the ambient temperature is 35° with 50mph wind (windchill 18°F) you will not get frostbite. The same way your batteries or floor will not get below 35°.
Dave in AZ
Well-known member
Sorry. But you're just not correct. You are assuming that heat transfer through air molecules is the only heat transfer, and you're wrong. Everything radiates heat... many things will also reabsorb the same amount of heat through conduction, convection, etc.
Making ice in a thermos, open to night sky, above freezing, is in Ch1 of every thermodynamics textbook ever written, to help demonstrate the various heat transfer methods to beginners.
However, I gave you the obvious example everyone has seen and knows, frost on windshield when air is above freezing, which you ignored.
Don't always want to try and fix stupid, it can make you look better.This thread is turning into an enjoyable engineering-fest
Martinjmpr
Wiffleball Batter
Well I'm flattered you would say that. I have no doubt that YOU could change out the converter in 30 minutes.
Me? I could potentially do it but it'd likely be an all day job with multiple trips to the auto parts store/home depot/emergency room.
Source: 62 years of experience being me.
rruff
Explorer
Yep... get an IR thermometer and point it at a clear night sky...
Not so much IR exchange between say, the trees and your rig... but the clear sky sucks up a lot of energy, and anything facing it will get cold. At night in an open area, clear sky, and calm conditions, I've seen a 30F difference between the roof and sides.
Dave in AZ
Well-known member
Yep. Every Boyscout used to learn to never set up a tent under clear sky, it it was possible to have a tree overhead, and you'd be much warmer.
Old Tanker
Active member
It shouldn't be hard to run two 4 AWG wires from your starter battery to an Anderson connector on the rear bumper, and then continue the wires to a DC-DC charger on the trailer. You wouldn't be reliant on solar in shade or winter, and you wouldn't be the rude jerk running a "quiet" generator in camp. As long as you drive a few hours every other day, your battery would be near full. Note, however, that your DC-DC doesn't always push its full output to the battery - after a bulk charging phase, it will drop down to an absorption phase - so a 40AH DC-DC won't get a 200 AH battery from zero to full in 5 hours.
rruff
Explorer
I can only assume that the OP will be parked for long periods, or at least will not be driving very far.
I asked earlier what the intended use case was for energy consumption and driving because I hadn't seen this mentioned. I thought simply adding batteries might be sufficient nearly all the time.
One issue with direct alternator charging is the often too-low voltage for LiFe.
I asked earlier what the intended use case was for energy consumption and driving because I hadn't seen this mentioned. I thought simply adding batteries might be sufficient nearly all the time.
One issue with direct alternator charging is the often too-low voltage for LiFe.
Peter_n_Margaret
Adventurer
I occasionally direct alternator charge my 320Ahr, 12V LiFePO4. The 85A alternator provides 14.2V which is ideal.
Adding more battery is a bit like opening a new bank account without any increase in income.
Cheers,
Peter
OKA196 motorhome
Adding more battery is a bit like opening a new bank account without any increase in income.
Cheers,
Peter
OKA196 motorhome
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Back to the first post. Since your Martinjmpr jumper cables charged your batteries, it seems you have sufficient alternator charging voltage at idle to provide some battery charging. Some, determined by monitoring.
All alternator equipped vehicles I've owned, at idle, attempt to charge the battery. The only way to know for sure is an accurate dc voltage reading in tenths of volts, and a way to measure DC amps. A clamp-on style multimeter provides both. There are accurate digital voltmeters that simply plug into the cigarette lighter/power plug. Some provide multiple outlets for charging other things.
If you see 14+ vdc you could do what Old Tanker and Peter stated, possibly without the DC-DC converter. If you ran the wire through one of these or similar, you could monitor charging amps and volts.
If you don't see 14+ volts, computer controlled alternators sometimes have ways to raise the voltage. My Silverado does when running park or headlights.
My simplest DC ammeter for yes/no is this vintage style that measures by simply holding it against a wire. I've used these styles since the sixties. Mine show 5 amps of solar panel current.
The supposedly quiet inverter generators have very limited 12vdc outputs, if at all. To charge batteries requires 12v chargers of some type with enough output amps and mid fourteen volts. More stuff. Fuel. Unpacking, repacking. Wires, connectors. Been there and sometimes am there still.
I really like alternator charging.
All alternator equipped vehicles I've owned, at idle, attempt to charge the battery. The only way to know for sure is an accurate dc voltage reading in tenths of volts, and a way to measure DC amps. A clamp-on style multimeter provides both. There are accurate digital voltmeters that simply plug into the cigarette lighter/power plug. Some provide multiple outlets for charging other things.
If you see 14+ vdc you could do what Old Tanker and Peter stated, possibly without the DC-DC converter. If you ran the wire through one of these or similar, you could monitor charging amps and volts.
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If you don't see 14+ volts, computer controlled alternators sometimes have ways to raise the voltage. My Silverado does when running park or headlights.
My simplest DC ammeter for yes/no is this vintage style that measures by simply holding it against a wire. I've used these styles since the sixties. Mine show 5 amps of solar panel current.
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The supposedly quiet inverter generators have very limited 12vdc outputs, if at all. To charge batteries requires 12v chargers of some type with enough output amps and mid fourteen volts. More stuff. Fuel. Unpacking, repacking. Wires, connectors. Been there and sometimes am there still.
I really like alternator charging.
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rruff
Explorer
I think it's more like carrying enough food on a backpacking trip, so you don't need to kill animals to keep from starving...Adding more battery is a bit like opening a new bank account without any increase in income.
Still don't know what the OP's use case is, though. Charging the batteries by idling the vehicle on a regular basis is not something I'd want to do...
One thing I don't recall being mentioned is the exhaust fumes.
WOW!
Not totally right on either issue...
Windchill is the result of how cold effects human skin in wind, it is a cooling effect, and while it does not have the same effect on other objects as it does on your skin, it can literally freeze your skin.
Asking Co-pilot;
You
can you get frost bite from windchillCopilot
Yes, you can. Windchill accelerates heat loss from your skin, which can lower your skin temperature and, in extreme cases, lead to frostbite. Protecting exposed skin is crucial in cold, windy conditions...Can objects be colder than the ambient temperature by natural means
Copilot
Objects typically can't be colder than the ambient air temperature without some external influence. However, when the air temperature drops, certain conditions can cause objects to cool even further due to processes like radiational cooling or evaporative cooling. Think of a wet object on a windy, cold day—it can feel colder as the water evaporates and removes heat.crazysccrmd
Observer
Based on everything I’ve been taught on Arctic exposure/survival and from personal experience you can’t get frostbite if the ambient temp is above freezing, regardless of a windchill value. You will absolutely lose heat faster but the exposed skin won’t drop below the ambient temperature and cause true frostbite. There are other cold weather effects that will cause injury but the flesh will not physically freeze. I’ve spent a lot of time with exposed skin while windchill values were well below 32F and have never seen anyone suffer frostbite.
Dave in AZ
Well-known member
Well, nothing like taking one anecdotal frostbite statement, and extrapolating it into a General Theory of Heat Transfer. That there is known as the Redneck Scientific Method.