Car battery to run diesel heater

[Spicyguy]

I keep going back and forth about how I'm going to keep the van warm this winter....diesel heater or wood stove. (If anyone has any very positive or negative things to say about either of these I'd love to hear it) 

Anyways, one of the main issues I have with diesel heater is how I'm going to take care of the battery needed to run it. I'm concerned about long spells without sun so solar will be potentially difficult and I will only be driving about an hour per day maximum so alternator charging will be minimal. From what I've seen, the 2kw versions need about 10amps at startup for a minute and then die down to about .9 amps or so. I'll need to run it for about 12 hours a day I figure. I was wondering if just getting a regular starter car battery would be a possibility and wire it in parallel with my other starter battery. Would a drain of around 12 to 15 amps off of this nightly be bad/damaging/ hard on alternator to recharge if driving for around an hour a day? Any experience with this would help! 

Thanks!

 

[MrAlvinDude]

I do not have any opinions (nor experience) about the differences or advantages of using either a diesel or wood heater for a vehicle.

I only have a few questions and comments about the possible scenario about the battery needs for the diesel heater solution.

Do I hear that you ask if it is feasible to double the capacity of your starter battery, and then simply use the 'big' starter battery to power the diesel heater at night?

Theoretically this might be possible, but let us do a math experiment.

Let us say that you need 15Ah per night.
- You should never discharge (use) more from your starter battery than 20% of its capacity.
- When only charging for one hour a day, the top 10% of the battery will never get charged, as the top 10% will only get charged slowly.
- when it is cold, the capacity of a lead acid battery is less. I think it is not unrealistic to think that only 50% is available when the temperature is below freezing.

These general numbers indicate that you should only plan to use 5-10% of the complete battery capacity. So with a starter battery of 150-300Ah you might be able to simply use the starter battery, and still retain a very high predictability in being able to start your vehicle in the morning.


Now, I do not really know if it is a good idea to have such a big starter battery in your vehicle, when considering how the load on your alternator will be.  As the bigger the battery, the more it can potentially allow when being charged.
What size (Ah capacity) is your current starter battery?

In my brothers van (sprinter diesel), the starter battery is 150Ah, and there is already room an auxiliary battery under the hood, so in his van it us very likely that another 150-300Ah extra will ever overload anything.


Then there is the consideration about how long is the starter battery likely to last, when being used in this particular use situation.

One hour of driving is likely to never ever fully charge the battery, so you resting battery voltage is likely to be under 12.8V, and this is not ideal for the longevity for a lead acid battery, but as long as you do get the resting voltage as close to 13V as possible, it is likely that your battery will live for a year or more.

Ideally a lead acid battery should live for several years, and if very careful monitoring and maintenance is done one can hope for batteries to last 3-7 years.


A few definitions
- Resting voltage: is the voltage that a battery will have some minutes (or hours) after it is no longer connected to a charge source.

- Careful monitoring and maintenance: being charged 3-4 times a week, so the resting voltage is above 13.5V, ideally close to 13.8V
Monitoring using a watt meter (includes a shunt resistor on the battery, for precise watt measuring), so one can do actual monitoring of remaining capacity of the battery. And so now more use than a decided limit 20%-40% use) will never be exceeded.


So this are some of the theoretical and optimal numbers. I hope they make sense to you.


But what if your standard starter battery is only 33Ah or 43Ah, and you double this capacity, so you end up with 66Ah or 86Ah?
Is it still possible to draw 15Ah every night from such a battery?  Well theoretically yes, it is possible in some (or most) circumstances. As 15Ah from 66Ah is less than 25% used energy, and from 86Ah is less than 20% used. But it is likely that the battery will wear out quickly (in less than a year), especially if the battery is cold when it is being used.
And it is highly likely the frequency of days where it is not possible to start in the morning will increase.



So what other (simple, easy and/or cheap) options are there?


* Separate your starter battery and house battery.
And use an automatic marine-style relay to charge the house battery.

Here is an example of a small and inexpensive automatic marine battery separator (max 125A)
https://www.biltema.dk/en-dk/boat/e...n-material/voltage-sensitive-relay-2000042018
The price on this web page is in DKK so 229DKK is about US$35


* Get a lithium starter pack, so you can always start your vehicle
For examples see: https://www.amazon.com/s?k=jump+start

This way, you might chose to do an experiment with using 2x 33Ah batteries for your starter battery. And see how long they will last, but you will still be able to start your vehicle.

 

[Gypsy Freedom]

first i will chime in on your choices for heat.

i love a woodstove fireplace in a cabin or home where i can deal with procuring and processing wood. in a mobile situation like a van or boat that is a whole nother thing. i have a sweet lil wood stove in my cruising sailboat. but i rarely use it as dealing with fuel supplies is a constant ongoing thing. even though i have access to all the wood i want piled up on the beaches and the forest i hike through. not like i can spend a weekend and load up on a cord of wood to get me though for a while. it becomes and almost daily task. also constantly tending the fire, waking up chilled in the night and having to decide if i should just pull on another blanket or get up and stoke the fire. so for me, as a regular heat source, wood stoves just dont cut it in small mobile situations. i do love it for the ambiance from time to time. sitting down t dinner with a glass of wine and the crackling of the fire. hard to beat.

i have yet to use one of the diesel heaters, but one is high on my list when some extra cash magically appears... lol

i built my own vented (exhaust fumes go outside via a "chimney") propane heater by blending the burner from a propane BBQ with the fire box and stove pipe of a cheap amazon wood stove. nice dry heat and a bottle of propane lasts a couple weeks when heating and cooking.


as for the battery for the diesel heater, i cant recommend strongly enough to stay away from using a starter battery. sure it will work, but it wont last long. even if you get a good warranty like walmart and replace it under warranty. that is just another dead battery going to the waste/recycle stream prematurely.

if you really just want the power to run the diesel heater. i would look at RC lithium batteries. you can find a 12v battery pack that should get you through the night with plenty to spare and they have chargers that will run from the ciggy lighter or othe connection to your car battery when. that should recharge quickly with the little driving you do and the lithiums for the RC stuff are designed for deep cycling

you might also shop around for one of the larger lithium "jump packs" that also has a 12 volt output fro running 12v devices. but check the charge times on those. some have a very slow long and drawn out charge time.

also trojan batteries makes a group 24 that is a deep cycle. not as good as golf cart batteries but will withstand the discharge cycles much better that a starter or even "RV" battery i think it is the Trojan SCS150 12V 100Ah Group 24 and i have found them at local distributors much cheaper than i can find them online. usually under $200

 

[MrAlvinDude]

I hope it is clear, that I fully agree with Gypsy Freedom, when recommending to NOT use the starter battery (even a double capacity starter battery)  for power in the diesel heater option.

But you did ask it it was possible, so I tried to give some information to illustrate that it is possible, but perhaps I did not say clearly enough, that it is definitely not the best way to do it. As a matter of fact, I would consider almost any other solution to be a better solituion.

 

[maki2]

The best little "woodstove" I have seen on youtube was one on the channel "Slim Potatohead". Just use that name plus "woodstove" to bring up the series showing how he made it and how it is used. While it can use wood his normal fuel system is for feeding it wood pellets. The wood pellets make it a lot more viable option than harvesting wood. The pellets are available in hardware stores, at places such as Home Depot and Lowes and at some of the farmer co-op stores. Much easier to store than chunks of wood an no need to resize it into pieces small enough to fit in a van sized mini woodstove. Now maybe you don't have the skills to build the stove he designed but you could hire a local sheet metal shop or welding shop to do the work for you.

I do think you should invest in a larger sized house battery if you want to have a diesel heater. Someday you might not want to drive anywhere and unless you have solar and/or a generator. You can use it for things other than the heater, it is a good investment. Try to stay connected with other nomadic travelers. Some of them are switching from AGM batteries to Lithium and you might be able to purchase their old AGM that is still has good function. Sometimes they are also changing out to larger solar panels and will be selling their still functional 100 watt panels.

I do have a diesel heater but it is not one of the types that most people are installing so discussing it won't be of any help as it is not a budget friendly purchase.

My recommendation is to eventually have both diesel and that small home built pellet stove. Redundancy has its benefits. Sometimes you might be in a location or are making a quick short stay where you don't want to have wood heat going so then the diesel heater will be a great alternative option.

 

[Gypsy Freedom]

A few definitions
- Resting voltage: is the voltage that a battery will have some minutes (or hours) after it is no longer connected to a charge source.

- Careful monitoring and maintenance: being charged 3-4 times a week, so the resting voltage is above 13.5V, ideally close to 13.8V
Monitoring using a watt meter (includes a shunt resistor on the battery, for precise watt measuring), so one can do actual monitoring of remaining capacity of the battery. And so now more use than a decided limit 20%-40% use) will never be exceeded.


So this are some of the theoretical and optimal numbers. I hope they make sense to you.

i trimmed this quote to save space, but there is a lot of misleading info that is very confusing to the inexperience person

starting batteries are NOT rated in amp hours. they are rated cold cranking amps and some will have a "reserve capacity" we need to use proper terminology so new people can learn correctly rather then get off on some misleading tangent

starting batteries need to be immediately recharged after use for best life. they are designed to dump large amounts of current for short times and then be recharged as soon as that engine starts. charging them only 3-4 times a week with impact their life span

the industry standard definition of resting voltage is when a battery as been resting 24 hours with no loads and no charge source. for standard flooded lead acid batteries this is usually around 12.7v usually you can get away with only resting a battery a couple of hours to let the surface charge bleed off. but if you are seeing high 13.x volts you are likely still reading a surface charge

also, relying on volt readings can be misleading in and of them selves. most calibrated consumer grade voltmeters are notoriously off. often by as much as a volt



the recommendation to isolate the starter battery from the house bank is a wise thing to point out

the voltage sensing relay you linked to is one way of doing it. there are many. note also on that link that the disconnect voltage is 12.8 volts. that is just slightly higher than the resting voltage of a fully charged lead acid battery in good condition. this is so when the charge source is removed one battery will not discharge the other as it is drawn down

the basic idea is to somehow connect the batteries in parallel when there is a charge source and disconnect them when there is no charge source, or it is not enough to keep up with the discharge. the linked voltage sensing relay does that by sensing when the voltage rises above the set point it connect them IF it has been wired in properly

you can also just use a constant duty rated solenoid that is triggered by an electric signal that is only present when the engine is running, it can also be a manual switch that you activate. you can also use electronic battery to battery chargers that will charge much faster and provide protections form over charging as well as isolation to prevent discharge. but they are a bit more money

the idea of the jump pack may have some merit, but most of the ones in the link provided do not have a 12v power outlet to power devices. they have the high current boost to start the car and some usb ports. and they take hours to recharge in the car from a usb source. you would need to find a jump pack that has a 12 output to connect devices and a capacity large enough to handle the expected load with some over head. be carful when looking at jump pack and power bank capacity specs. most, almost all of them list the miliamphours. but they list the mili amp hours of the cells, at the cell voltage. so 50,000 mili amp hours at 3.x volts is about 14th the miliamp hours when adjusted for a 12 volt output. finding one that can provide 12v source with a decent capacity and that can be rechared quickly has been a challenge. if you know of one that does, please link the product so i can check it out. i am on the hunt for one my self

 

[Gypsy Freedom]

mralvindude, agreed

it is possible, may have done it and continue to do it

just not the best or recomended way to go about it

 

[Gypsy Freedom]

thanks maki2, for the slim potato head reference. i need to check that out. i have oft wondered if pellets could make life easier for wood heat in a mobile life

 

[MrAlvinDude]

i trimmed this quote to save space, but there is a lot of misleading info that is very confusing to the inexperience person

I thank you for expressing your opinion

starting batteries are NOT rated in amp hours. they are rated cold cranking amps and some will have a "reserve capacity" we need to use proper terminology so new people can learn correctly rather then get off on some misleading tangent

hmmm...  I suppose this will then depend on the market where they are sold.
Where I live, all batteries are sold with a Ah statement. And Cranking numbers can be difficult to obtain.

But it is good to know that in the US market things are as you have described. I will be more mindful about this in the future.

starting batteries need to be immediately recharged after use for best life. they are designed to dump large amounts of current for short times and then be recharged as soon as that engine starts. charging them only 3-4 times a week with impact their life span

I believe it is best for all lead acid batteries to be charge as soon as possible, but accept that this holds particular true for starting batteries, because of their different internal design. 

the industry standard definition of resting voltage is when a battery as been resting 24 hours with no loads and no charge source.

Okay. I see that I should not only have used the word 'definition', but have used the words 'definitions in this post'.  
As well as I am now more likely to specify the benefits of looking at the numbers after 24 hours of resting. 

for standard flooded lead acid batteries this is usually around 12.7v  usually you can get away with only resting a battery a couple of hours to let the surface charge bleed off. but if you are seeing high 13.x volts you are likely still reading a surface charge

Makes sense, as I have never really been patient enough to wait 24 hours to get a voltage reading. I usually just wait until I basically no longer see any voltage change - for 30 seconds or so. 

also, relying on volt readings can be misleading in and of them selves. most calibrated consumer grade voltmeters are notoriously off. often by as much as a volt

hmmm....  I suppose we think differently about 'calibration' then.

But we agree that different measuring instruments typically will show different results.
As the old saying goes: A man with only one watch will always know what time it is, but a man with two watches never knows.

So I try to always use readings where I can get one or two decimals more than what I need.
Likewise, if the reading really matters, then I will compare readings from several different meters.
Or I will simply go with what the more expensive meter says.

the recommendation to isolate the starter battery from the house bank is a wise thing to point out

the voltage sensing relay you linked to is one way of doing it. there are many. note also on that link that the disconnect voltage is 12.8 volts. that is just slightly higher than the resting voltage of a fully charged lead acid battery in good condition. this is so when the charge source is removed one battery will not discharge the other as it is drawn down


the basic idea is to somehow connect the batteries in parallel when there is a charge source and disconnect them when there is no charge source, or it is not enough to keep up with the discharge. the linked voltage sensing relay does that by sensing when the voltage rises above the set point it connect them IF it has been wired in properly

Ah yes, I see how my impatience about noting the resting voltage has not helped me to get this clue about the 12.8V in that device, before just now.

And I also see why it is beneficial to not re-engage the charging of the house battery, until the voltage reading is 13.2, as this will give the starter battery time to get a good head start on the charging. As well as it will lower the initial load on the alternator, as only one battery at a time will have a low voltage state, and thus be able to accept a high amp load from the alternator.

 

[Gypsy Freedom]

ah mralvindude, out of curiosity where about in the world do you hail from. i often forget that the world does not revolve around the USA (lol), please accept my apology.

thanks

 

[MrAlvinDude]

Hi Gypsy Freedom,
I hail from Scandinavia, more specifically Denmark.

And no apology is necessary. We are all here to learn. So I thank you for sharing, as it has already made me wiser about things that were not clear to me before.

And I hope to learn more in the near future. 


See you around

 

[Firebuild]

* Get a lithium starter pack, so you can always start your vehicle
For examples see: https://www.amazon.com/s?k=jump+start

This way, you might chose to do an experiment with using 2x 33Ah batteries for your starter battery. And see how long they will last, but you will still be able to start your vehicle.

Boy, do I second the lithium starter pack.  This is the second time today I've posted a link to one of my videos, and i'm not trying to be self-promoting, I swear, but I demonstrate one in this video after my battery needs a little help. Why? Because of running the diesel air heater off the starting battery! Here's the video if you want to see the jump starter. It's a pretty handy little device. 

I am more or less an idiot compared to the knowledgable folks who have weighed in so far, but I do have one area of expertise in that I currently have a diesel air heater that I run off of my starting battery. As evidenced by the video I just talked about, I don't recommend it.

Though the heater really doesn't draw a lot, my 7.3L diesel engine likes a very full battery for cold starts. When I put this setup together last winter, I had nightly access to shore power, and I was keeping both a block heater and a battery maintainer plugged in all night.  In that situation, running the heater had no real consequence that I could see. I was able to start up without issues, even if the bus sat a few days without being used.

It's cold already now, and I don't have shore power this year.  The heater doesn't come close to draining the battery, but combined with the extra cranking I'm doing because I don't have a way to plug in my block heater, it's getting just low enough that I need my lithium jump starter to get going. I don't know for sure, but I'm guessing daily jump starting is not recommended.

You mentioned running it for 12 hours. I don't know where you're located or how big your vehicle is, but the longest I have ever run the heater in one stretch is 3 hours, no matter what the ambient temperature is, because it heats things up wel enough to shut it offl. The only issue I have is that my bed is all the way in the back and the heater is located under the driver's seat, so on a super cold night the hot air is at the ceiling level by by the time it gets to me. The floor can be icy. I have solved that with a long duct that brings the heat more directly to where I'm sleeping, BUT I mostly just use a 12v electric blanket at night and turn the heat off.

I have a small portable solar unit (also chargeable from the cig lighter or an ac outlet) that I may set up as a dedicated power source for the heater.

 

[maki2]

Hi Gypsy Freedom,
I hail from Scandinavia, more specifically Denmark.

And no apology is necessary. We are all here to learn. So I thank you for sharing, as it has already made me wiser about things that were not clear to me before.

And I hope to learn more in the near future. 


See you around

There are some very nice diesel heaters in the Nordic countries that were developed for use on boats. That is the type of have, it is a diesel fueled cooktop that also has a heating function.

 

[RogerD]

I just got a 2kw heater to test and see how cost-effective it is compared to my wave 3 heater.

It supposedly uses around 10 amps on startup when it heats up the glow plug. I believe this is for around 3-5 minutes. It will do the same thing when you stop it. How many amps it uses in between will depend on the setting you have it set at. I will know for sure once I test it.

If you are going to get a 2kw heater, you really have to be careful because many 5kw heaters are misrepresented as being a 2kw heater. Also, you will seem some listed as 2-5kw, it's a 5kw heater.

The 5kw heaters are around 400mm or so in length. The 2kw heaters are around 300 mm in length.

The 5kw heater on the lowest setting is around 5K BTU. The 2kw heater is around 3K BTU.

There are a bunch FB groups that just about them that you can learn more about them.

I highly recommend watching this guys videos.

https://www.youtube.com/user/johnmck1147/videos

I got this one and it's a genuine 2kw heater.

https://www.ebay.com/itm/ty-2KW-12V...itch-For-Truck-Boat-Trailer-Fast/264462807848

 

[wb8vyn]

I keep going back and forth about how I'm going to keep the van warm this winter....diesel heater or wood stove. (If anyone has any very positive or negative things to say about either of these I'd love to hear it)

Anyways, one of the main issues I have with diesel heater is how I'm going to take care of the battery needed to run it. I'm concerned about long spells without sun so solar will be potentially difficult and I will only be driving about an hour per day maximum so alternator charging will be minimal. From what I've seen, the 2kw versions need about 10amps at startup for a minute and then die down to about .9 amps or so. I'll need to run it for about 12 hours a day I figure. I was wondering if just getting a regular starter car battery would be a possibility and wire it in parallel with my other starter battery. Would a drain of around 12 to 15 amps off of this nightly be bad/damaging/ hard on alternator to recharge if driving for around an hour a day? Any experience with this would help!

Thanks!

Nope. Car starting batteries are designed for Short duration High current use.. More or less surface charge replacement. So even though you can discharge them more slowly over an hour or two, The battery will NOT recharge to new capacity by a few percent after each long duration discharge.
The cycle life over time will be depleted quickly.
You need a deep cycle battery for your heater use.
Prices very from under $100 to near $1000 for such batteries.
I use deep cycle marine batters to run my diesel heater, 100 amp hour.
There is a draw back to consider. Deep cycle batteries have to be charged more slowly (less charging amps over longer periods of time).
The math is simple. Heater draws about 5 amps. Continuous. 5 amp draw over 1 hour equals 5 amp hours. Run the heater for 10 hours at 5 amp draw equals 10 times 5, total 50 amp hours. A 100 amp hour deep cycle battery will be half empty.
Now you must replace the 50 amp hours. Say you recharge at 5 amps from a source such as a battery charger or solar panel system, it will take 10 hours to bring the battery back to full again. Remembering that deep cycle batteries should be recharged over longer periods of time. One hour at a high rate from car alternator will recharge more quickly but the deep cycle battery will suffer a shorter life. so a current limiting devices is advised.