How long can a car run at idle (stationary) to charge a battery bank like a Delta or two?
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Jasgeer
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You need to know the amp output of the alternator at idle. A 100 Amp Alternator is rated at higher rpm. You could use a clamp on ammeter. At idle you may only be getting 25-30%. Once you know the Amp output you will know how much charging you are getting per hour. If you reduce the size of the pulley on the alternator you will get more Amps for the same engine speed.
schmism
Solar Addict
I know you already have the car but it would be much more efficent to go buy a small gas powered generator and charge the solar generator off it, not to mention the wear and tear on the car.
Jasgeer
New Member
After thinking more about it I think you might be best served by purchasing a DC-DC charger so there would be a target value of the current being delivered to the storage battery. For example: Renogy makes DC-DC chargers that are rated for 20, 30 or 40 Amps and are buck/boost meaning that they can either decrease or increase the voltage and have charging profiles for different battery chemistries. I use a Renogy 20A and it was just over $100. I use it for charging while towing the trailer.
You didn't state the type of vehicle. You might be able to install a higher amperage alternator.
MisterSandals
Participation Medalist
Good point. The alternator needs (expects) airflow so having the hood open and even a small 12v fan blowing on alternator would help.
I have a dual fuel 4,000 watt generator and 60lbs of propane that would last only a couple of days. I don't want to STORE gasoline except in the 18 gallon tank in my vehicle. I want to use the vehicle as backup charging station for the Deltas for when the genny is out of propane. Efficiency is a second priority when one is out of first priority fuel.
Actually my plan is this:
1) Short term outage, a few hours to a day or so, the Ecoflow Deltas
2) Two to three day outage - Deltas charged by combo of solar and propane generator
3) Three to six+ day outage - Deltas charged by combo of solar and whatever duration my car can charge.
4) Longer than six or seven days - Charge Deltas by solar (3, 195 watt panels in series gets close to 400 actual watts)
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When the SHTF, priorities change.
OTRwSolar
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IMO, way too many variables to answer your question with any accuracy at all. If it's that important to know I'd suggest a realworld test. Fill up your car with gas, run it for a few hours (under load charging), then fill it up again to establish some kind of GPH baseline. Should be able to roughly calculate maximum runtime for a full tank of gas based on this baseline.
How about simply: How long will vehicle x run stationary at idle on x gallons of gas?
Jasgeer
New Member
An alternator tends to be self-protective as they come from the factory and used for the purpose intended. At idle they put out very little current (perhaps only 25-30%) so they are probably not capable of overheating. They barely produce enough current to break even with the ignition, electronics, etc. At cruise rpm that are putting out much more current and the integral fan is working to keep them from overheating. The problem comes when you add a Lithium cell to be charged. If discharged and >~100 AHr, a Lithium battery represents a low impedance load which needs to be charged for a for a long period of time. Adding a DC-DC charger limits the current drawn from the auto system (hopefully) to a safe value. Victron has videos on the issues of using an alternator directly charging Lithium batteries. Balmar (the marine folks) make some alternators with external regulators that incorporate temperature sensing of the alternator windings to back off the Amp output to limit the heat produced. This is probably the safest approach when charging Lithium directly from an alternator.
But there seems to always be another problem to solve and that is Load Dump. Load Dump can destroy electronics. The only safe way to interrupt a high current flowing from the alternator without causing a Load Dump transient is to remove power to the Field winding BEFORE removing the load. I don't know of any BMS with this capability. That is why some people add large transient protection devices (aka snubbers) like the ones from Stirling near the output from the alternator.
OTRwSolar
Solar Enthusiast
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Whatever works for you.
You're assuming the alternator presents little to no load on the engine. That may not be true for all applications.
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Jasgeer
New Member
The issue is that the alternator does not output much current at idle. It does fine at cruise rpm. You could use a smaller pulley on the alternator to boost its rpm. This is often done in emergency and police vehicles that idle a lot.
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Install a T in your vehicle fuel line (or some other location to tap in) with a valve and several feet of fuel line. Install a power switch for the fuel pump, if you dont want to or dont know how to install the switch you can simply cycle the ignition key as many times as required to fill your generator. If you need fuel, open the valve and stick the hose in the generator tank, turn the pump on with the switch or cycle the key until you have enough fuel in your dual fuel generator. Fuel storage problem solved.
Exactly, it also overworks the alternator unless you upgrade to a higher output. I tried all sorts of ways to get it to work. We traveled the country doing gun and knife shows and found panels on the van made it a target. Harassment by cops assuming we were stealth camping anywhere we stopped was normal. Go to Walmart, shop find a cop telling you to move on, eat at a restaurant and same thing. Thieves also know you have electronics if you have solar. Id like to add we never once stealth camped. My point,, we tried all sorts of ways to charge the battery, 200 watts of panel put out while camping did the trick, on drives of 2 or more hours at interstate speeds we usually had a full battery without putting out panels.
Thanks. Great advice for a mechanic, which I am not and have no desire to be.Install a T in your vehicle fuel line (or some other location to tap in) with a valve and several feet of fuel line. Install a power switch for the fuel pump, if you dont want to or dont know how to install the switch you can simply cycle the ignition key as many times as required to fill your generator. If you need fuel, open the valve and stick the hose in the generator tank, turn the pump on with the switch or cycle the key until you have enough fuel in your dual fuel generator. Fuel storage problem solved.
Its something you could pay a mechanic 30min to do. Idling your car for hours on end is going to cost you more than paying someone knowledgeable to do the small hack.
I will be using this ** https://www.amazon.com/gp/product/B01N5W6HTG/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1 ** connected to my battery. There will always be the car battery in my vehicle alternator circuit.
Wouldn't it be simpler (and also perhaps cheaper) to just get a couple more propane tanks and keep them filled for the emergency. Propane stores for years and you would not have to mess around with hooking up the car as a charging source. Likely 4 or 5 of the BBQ sized tanks should roughly equal your car's tank of gas...
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