Using car as Temporary Generator - Idling for 45 minutes or more

[d215yq]

Hi all,

Due to the lockdown I'm likely having to leave the city this week where i have no electricity and have built an electric off-grid system. The problem is I bought a inverter that incorporates a solar charger that needs 120V of panels minimum to work and i only have 40V of panels so I have normal electric power direct from inversor in daylight but no way to charge the batteries for a week until my extra panels arrive (they don't fit in the car!!)

So long story short I would like to keep two 12V AGM 75aH batteries topped up once everyday to allow for internet/phone charging and some basic light, etc at night. My calculations are based on 0,3kWh use/night that's 15aH or about 45 minutes.

Is 45 minutes an Ok time for the car to be idling if I check it doesn't overheat? It gets a lot of long journeys (600km just this weekend) so should have the carbon cleared out pretty soon.

I've measured the regulator voltage at 13.9 @ idle and my battery says charging from 13V to 15V so I assume that means it's compatible. I'd also charge them in parallel to ensure they are the least likely to be overcharged and ruined. As it's an old school diesel W124 no sensitive electronics to fry in the car either.

And yes, before the smart alecs come on with solutions like "buy a generator", it's a temporary solution I'm proposing which I'm likely to be forced into by extreme measures outside my control. Just wondering if there are any serious problems it will cause to either the batteries or the car, or if it's just an inefficient but safe way to charge stuff and allows me to keep workign and communicated after dark for a few days until my panels arrive!

 

[umblecumbuz]

Can't see a problem with 45 minutes idling.
Many on here - especially those living in really congested countries - have their cars idling for longer periods on a regular commuting/traffic jam basis, with no ill-effects other than fuel wastage and the need for an Italian tune-up.

 

[M80]

Taxi drivers seem to sit engines running for a good while.
In Siberia they are afraid a car won't restart after a night at very sub zero temperatures so leave their vehicles (specifically diesels I guess) ticking over all night.

I don't see the over charging issue at 13 volts.
But another choice could be to rune an intelligent battery conditioner from an invertor powered from the car. That is 12 volt invertor plugged into the car, 230 volts from invertor with charger plugged into that.

Be sure the batteries are the same to avoid circulating current between the 2.

 

[d215yq]

Taxi drivers seem to sit engines running for a good while.
In Siberia they are afraid a car won't restart after a night at very sub zero temperatures so leave their vehicles (specifically diesels I guess) ticking over all night.

I don't see the over charging issue at 13 volts.
But another choice could be to rune an intelligent battery conditioner from an invertor powered from the car. That is 12 volt invertor plugged into the car, 230 volts from invertor with charger plugged into that.

Be sure the batteries are the same to avoid circulating current between the 2.

Hmmm...the batteries are the same and brand new but obviously different from the car battery itself. If I had an intelligent charger I could just run it off the house power in the day (the inversor uses the 40V photo voltaic input to 230V fine and also the 24V battery to 230V) it's just it confusingly needs 120V photvoltaic input to activate it's built in battery charger, so I have the power i need in the day but the batteries don't get charged. I suppose I could just change my flexible working hours to those of the sun and then a 10W LED at night will probably allow the batteries to last a week anyway until the other 80V of panels arrive.

Another thing I was thinking which is probably a bad idea is to just swap a half charged battery for the car battery itself before I need to go somewhere and it'll charge up normally with driving. There's probably a reason not to do that, though i can't think why not.

 

[Uncle Benz]

A pal of mine on the Isle of Wight had to live in a caravan last winter while they were buiding a house. He used an old diesel peugeot and a heat exchanger and pump to run central heating in the caravan. That was idling for three months. You’ll be fine!
I have some pictures somewhere

 

[Tony Dyson]

Hi all,

Due to the lockdown I'm likely having to leave the city this week where i have no electricity and have built an electric off-grid system. The problem is I bought a inverter that incorporates a solar charger that needs 120V of panels minimum to work and i only have 40V of panels so I have normal electric power direct from inversor in daylight but no way to charge the batteries for a week until my extra panels arrive (they don't fit in the car!!)

So long story short I would like to keep two 12V AGM 75aH batteries topped up once everyday to allow for internet/phone charging and some basic light, etc at night. My calculations are based on 0,3kWh use/night that's 15aH or about 45 minutes.

Is 45 minutes an Ok time for the car to be idling if I check it doesn't overheat? It gets a lot of long journeys (600km just this weekend) so should have the carbon cleared out pretty soon.

I've measured the regulator voltage at 13.9 @ idle and my battery says charging from 13V to 15V so I assume that means it's compatible. I'd also charge them in parallel to ensure they are the least likely to be overcharged and ruined. As it's an old school diesel W124 no sensitive electronics to fry in the car either.

And yes, before the smart alecs come on with solutions like "buy a generator", it's a temporary solution I'm proposing which I'm likely to be forced into by extreme measures outside my control. Just wondering if there are any serious problems it will cause to either the batteries or the car, or if it's just an inefficient but safe way to charge stuff and allows me to keep workign and communicated after dark for a few days until my panels arrive!

Have you checked the alternator output rating, these machines are designed to charge the on board battery and electrics and you are considering to add two more potentially discharged 75Ah batteries directly onto the car, the additional charging load will be significant, not just for the alternator but all the connected charging components. To install an interface between the car and the additional charging installation, as @M80 suggested above would be a good idea but I would suspect the electrical load in the primary 12v feed to an inverter would be so great it would be an impractical solution. Without a lot of complicated calcs for which you would need specific details of all your involved components, the only way you could do this confidently would be to disconnect your car battery and use jump leads to charge your two additional batteries separately,... OR, "buy a generator" , If I were designing an off grid installation, a standby generator would be a necessary and integral part of the design rather than a smart alec suggestion.

 

[d215yq]

Have you checked the alternator output rating, these machines are designed to charge the on board battery and electrics and you are considering to add two more potentially discharged 75Ah batteries directly onto the car, the additional charging load will be significant, not just for the alternator but all the connected charging components. To install an interface between the car and the additional charging installation, as @M80 suggested above would be a good idea but I would suspect the electrical load in the primary 12v feed to an inverter would be so great it would be an impractical solution. Without a lot of complicated calcs for which you would need specific details of all your involved components, the only way you could do this confidently would be to disconnect your car battery and use jump leads to charge your two additional batteries separately,... OR, "buy a generator" , If I were designing an off grid installation, a standby generator would be a necessary and integral part of the design rather than a smart alec suggestion.

I see your point there. I will disconnect the battery and do one at a time for maximum security and then it can't overload the system.

I'll be honest and say I've had to rush the design of the system as I may need to live there permanently with 12h notice with all these new "house arrest" measures that are being brought in here: A lockdown here is not like the English concept and I will not endure that in my flat. Hence "messing up" with buying the wrong inverter charger as the right one had a delay of 3 weeks. The thing is it is making me buy more panels than I want (1,7kW of panels to reach the voltage) which means that on a winters day I'll have 7kwH of power and in summer nearer 12kwH. As my daily power usage will be max 2 to 3kwH not sure why I need a generator, I think i will eventually need another 4x batteries instead for smoothing the power but will have an excess power overall so don't want to add to that problem with a bulky, expensive generator .

That said, this inverter does have a feed to receive a supply from a generator and even capability to automatically start it and stop it when required (not sure how) so if I need one in the future it should be OK.

 

[M80]

My thinking, and open to better suggestion.

Using one of these
8A Smart Automatic Car Battery Charger Jump Starter Pulse Repair 12V 24V AGM/GEL | eBay
with an 8 amp output would mean more than 8 amps input from the cars 12 volt system. But not masses more and within the 15 amp fuse protecting the ciggy lighter.

This is 112 watts and wouldn't require a large invertor, but possibly larger than the 205 watts allowed by that 15 amp fuse (at 13.7 volts), as the invertor voltage falls off with load (from experience).
With the significant currents to the invertor at start up that would cause significant volt drop and so a drop in current anyway. The question is would the invertor fail if the volt drop is significant or recover after the initial surge?

Btw, charging one battery at a time reduces potential issues. I know these chargers can't handle the 150 Ahr they are rated at, I tried on the yacht.

 

[Rob76]

Have you checked the alternator output rating, these machines are designed to charge the on board battery and electrics and you are considering to add two more potentially discharged 75Ah batteries directly onto the car, the additional charging load will be significant, not just for the alternator but all the connected charging components. To install an interface between the car and the additional charging installation, as @M80 suggested above would be a good idea but I would suspect the electrical load in the primary 12v feed to an inverter would be so great it would be an impractical solution. Without a lot of complicated calcs for which you would need specific details of all your involved components, the only way you could do this confidently would be to disconnect your car battery and use jump leads to charge your two additional batteries separately,... OR, "buy a generator" , If I were designing an off grid installation, a standby generator would be a necessary and integral part of the design rather than a smart alec suggestion.

Could a voltage sensing relay be used for each battery to avoid overloading the alternator?

 

[Tony Dyson]

I see your point there... so don't want to add to that problem with a bulky, expensive generator .

Hmm, tell me that one again after your first power failure one dark winter's rainy night

 

[Tony Dyson]

My thinking, and open to better suggestion.

Using one of these
8A Smart Automatic Car Battery Charger Jump Starter Pulse Repair 12V 24V AGM/GEL | eBay
with an 8 amp output would mean more than 8 amps input from the cars 12 volt system. But not masses more and within the 15 amp fuse protecting the ciggy lighter.

This is 112 watts and wouldn't require a large invertor, but possibly larger than the 205 watts allowed by that 15 amp fuse (at 13.7 volts), as the invertor voltage falls off with load (from experience).
With the significant currents to the invertor at start up that would cause significant volt drop and so a drop in current anyway. The question is would the invertor fail if the volt drop is significant or recover after the initial surge?

Btw, charging one battery at a time reduces potential issues. I know these chargers can't handle the 150 Ahr they are rated at, I tried on the yacht.

Controlling the charger's output to say a roof of 10A would work with the supply from a cigar charger socket but I don't know what charger the OP has?

 

[A.J.]

Can't see a problem with 45 minutes idling.
Many on here - especially those living in really congested countries - have their cars idling for longer periods on a regular commuting/traffic jam basis, with no ill-effects other than fuel wastage and the need for an Italian tune-up.

Except for the fact there is a fixed penalty of £20.00 for that

 

[d215yq]

My thinking, and open to better suggestion.

Using one of these
8A Smart Automatic Car Battery Charger Jump Starter Pulse Repair 12V 24V AGM/GEL | eBay
with an 8 amp output would mean more than 8 amps input from the cars 12 volt system. But not masses more and within the 15 amp fuse protecting the ciggy lighter.

This is 112 watts and wouldn't require a large invertor, but possibly larger than the 205 watts allowed by that 15 amp fuse (at 13.7 volts), as the invertor voltage falls off with load (from experience).
With the significant currents to the invertor at start up that would cause significant volt drop and so a drop in current anyway. The question is would the invertor fail if the volt drop is significant or recover after the initial surge?

Btw, charging one battery at a time reduces potential issues. I know these chargers can't handle the 150 Ahr they are rated at, I tried on the yacht.

Or I just buy that (didnt realise it was so cheap) plug it into my mains in the day and charge the batteries from that, then reconnect the charged batteries to the inverter at night. Then no need to bother with the car at all...

 

[d215yq]

Controlling the charger's output to say a roof of 10A would work with the supply from a cigar charger socket but I don't know what charger the OP has?

I don't have a charger! hence making the alternator off the car charge it. But if I can get a charger for 15 pounds then that's fine, I'll pick one up today!

 

[M80]

So I thought I would find out if my suggestion was feasible.

Because I have been working on the Viano installing cameras I flattened the battery enough for a failed start. So it has been on charge with one of the above chargers to keep the battery topped while I run the HU and whatever.

I've the yacht batteries in the garage, both 75Ahr, but charged and already showing 12.7 volts each.

My 150 watt invertor is supposedly 300watt max (but no chance in reality).

Invertor into the rear ciggy lighter, always on supply anyway.
Charger into that,
and that to one 75Ahr battery.
Initially it was charging at close to 6 amps, but soon dropped back to less than 2 amps.
Starting the engine made little or no difference.

Soon enough the charger went into standby as the battery was already pretty well charged, so not really an ideal test that simulates your scenario. But I see no reason why this set up wouldn't work for you, with one battery at a time being charged.

The charger monitors and restores charging as battery voltage falls, so was ideal for shore side power to keep the yacht batteries topped up, if it could handle 150Ahr, which it can't.

 

[d215yq]

Hmm, tell me that one again after your first power failure one dark winter's rainy night

To be fair i've lived there for weekends for 3 months without any power whatsoever so I think I could cope... I can manage the power use easily but I suppose have no back up if the inverter itself fails...

 

[Tony Dyson]

Could a voltage sensing relay be used for each battery to avoid overloading the alternator?

I can't think of a way that it could?

 

[Rob76]

I can't think of a way that it could?

fair enough; my mind went straight to leisure battery setup for campers and the like

 

[Craiglxviii]

The only problem you’ll have is the alternator output.
No problem for your car to idle all day long.

 

[umblecumbuz]

Except for the fact there is a fixed penalty of £20.00 for that

In Spain, in the wilds - the middle of nowhere?