Inverter/ battery question

[DerekH]

Hi guys, question here. I have an 01 EB 50 with a 5.4L. The van has a 2500 Xantrex inverter. I added a Bosch 2.5 gallon water heater and only plan to use it while the engine is running as to not tax the battery too hard. I have a lifeline agm, 200 AH battery. The setup worked great for a while but I think the battery was on its way out. It is heating less now even with the engine running and the battery dips down to around 10v while the water heater cycles on. I want to replace the battery but don’t want to ruin a new one. Am I correct in thinking that as long as the engine is running the battery should be fine? Kind of confused here.
Thanks
Derek

[Lilnuts2]

Most alternators at idle barely put out enough voltage to keep the system level without a load on it. Next time you have a chance try running your motor up to 11 or 1200 RPM and see if it doesn't charge enough then. Or if you have a multimeter and know how to read it you could do it that way, by Measuring your amp output at certain RPM's

It could be a combination of old alternator and/or battery or either one the multimeter will tell you the story.

[posplayr]

Originally Posted by DerekH

Hi guys, question here. I have an 01 EB 50 with a 5.4L. The van has a 2500 Xantrex inverter. I added a Bosch 2.5 gallon water heater and only plan to use it while the engine is running as to not tax the battery too hard. I have a lifeline agm, 200 AH battery. The setup worked great for a while but I think the battery was on its way out. It is heating less now even with the engine running and the battery dips down to around 10v while the water heater cycles on. I want to replace the battery but don’t want to ruin a new one. Am I correct in thinking that as long as the engine is running the battery should be fine? Kind of confused here.
Thanks
Derek

Derek, You did not list what water heater you are using but if it is similar to this one, it pulls 12Amps at 120VAC. At 80% invertor efficiency that is going to be 120/0.8=150 Amps @12VDC.

As Lilnuts2 has explained, you can do some measurements to confirm what is going on, but for these types of power demands, it is pretty obvious what is likely going on without any further information.

A stock alternator is not going to be able to supply that amount of current at under 3K RPM so you are more than certainly cycling your AGM battery to a low depth of charge and killing its useful life.

Even the 2500 watt invertor cooreponds to a 2500/12/0.8=260 Amp DC demand.

https://www.homedepot.com/p/Bosch-2-...E&gclsrc=aw.ds

I think you are correct in questioning if this is the correct setup. It works for a while but will accelerate the demise of your AGM. A better but more expensive solution is to add a lithium battery for your house battery that is charged from a DC to DC convertor. Without solar or shore power charging this would be pretty straightforward.

People can struggle to even charge a 40 Amp DC to DC for the Lithium because at low RPM it can demand 60 amps DC from the chassis battery. But with lithium, you can colocate the house battery with the invertor and efficiently deliver these types of amps without affecting your chassis battery or alternator.

Given your results with the 200 AmpHr AGM, you might be able to get away with 100 Amp-hr of LifePO because the charge cycles are going to be higher. depending upon what you chose you might be able to do this for $1000 minimum and go up from there.

The other options are an on-demand gas water heater (under $200) or a more traditional gas water heater with a heat exchanger to use coolant to heat the water in addition to gas (probably $500+).

The bottom line is that the 12V electrical current demands for such a setup are very high using conventional lead-acid batteries.

Any type of resistive load for heating is going to be a high demand, and heating water is especially high (e.g. compared to heating air)

[REF]

Yup…..^
Depending on your intended use, I have the eccotemp version of this, there are others, simple setup and efficient. If you’ve got an on board propane tank, you can add an extend-a-stay adapter in line off your tank to have a readily available outlet to tap into. I integrated my unit into the cavity on the back door.

Camplux 5L Outdoor Portable Water Heater, 1.32 GPM Tankless Propane Gas Water Heater for RV, Camping, Barns, White https://www.amazon.com/dp/B08Z8D2XZQ...Q0S49J6EM46DQY

[DerekH]

Thanks for the replies guys. I guess I had always figured as long as the inverter was bigger than the wattage I would be fine with the engine running. Don’t want to ruin a new battery so I’m thinking maybe the propane option might be better. I do have propane so tapping into it should be pretty simple. Anyone have a pic of how they mounted a propane heater on the back door?
Thanks

[posplayr]

Originally Posted by DerekH

Thanks for the replies guys. I guess I had always figured as long as the inverter was bigger than the wattage I would be fine with the engine running.

High current demand (>100 amps) mostly always comes from a battery. Both inverter and water heater are well above that so running the engine helps (you could easily deplete a battery and be stranded with the engine off) it doesn't actually overwhelming supply the required current.


If you were running the water heater and were showing 10V engine running (at the battery) , it is unlikely you could get the engine to start.

If nothing else the voltage should be at 14V idling and with the heater on you drop to 10V! That is -4V drop! You can assume that the drop from 14-12.8V=1.2V means the alternator is tapped out. And then the 2.8V drop is a big load or overtaxing even the battery.

You would need to refer to lead-acid battery discharge curves, but generally, you never want to be discharging sitting at idle (less than 12.5V). You could do it for short periods of time, but heating 2.5 gallons of water is not a short period.

The longer I write the more this sounds like a ramble. The main thing to keep in mind is that high current demand comes from batteries, and the alternator is there to recharge over extended periods. You loads are all high demand (>100 amps) !

[DerekH]

Ok gotcha, thanks for the reply! I think a portable propane heater is in my future.

[maxswasser]

Originally Posted by REF

Yup…..^
Depending on your intended use, I have the eccotemp version of this, there are others, simple setup and efficient. If you’ve got an on board propane tank, you can add an extend-a-stay adapter in line off your tank to have a readily available outlet to tap into. I integrated my unit into the cavity on the back door.

Camplux 5L Outdoor Portable Water Heater, 1.32 GPM Tankless Propane Gas Water Heater for RV, Camping, Barns, White https://www.amazon.com/dp/B08Z8D2XZQ...Q0S49J6EM46DQY

Do you have a photo of this? I would definitely be interesting in seeing this. My propane is at the rear of my van, and water at the front. Better to run water or propane down the van do you think?

[posplayr]

Originally Posted by maxswasser

Do you have a photo of this? I would definitely be interesting in seeing this. My propane is at the rear of my van, and water at the front. Better to run water or propane down the van do you think?

I think the bigger issue is where to run the exhaust out of heater especially if you have a window van.

From what I have seen they are usually temporary hook up out the back or a back window is replaced with a metal insert.

[DerekH]

Ok thanks, is a bigger alternator an option?