Help me understand: How does a fridge not drain away your battery?

[jdlobb]

Sorry if this is covered in other threads, but I have been looking and missed it.

I'm interested in adding a fridge, probably one of the moderately priced ones, my eye is currently on the Indel B TB31.

But i'm a little terrified of waking up in the morning and not being able to start my truck.

Now, this doesn't SEEM to be an issue, or why would anybody have them? But I don't understand exactly why. How much power do they draw? Do you HAVE to have a backup power source like a Goal Zero generator or a dual battery set-up to use one safely?

 

[ChasingOurTrunks]

Great question, jdlobb. Two answers, but the most direct to your thread title: They DO drain the battery.

Solution 1) Dual Battery system. Many folks fit these specifically to ensure that they can meet their 12V demands in camp (Fridge, lights in camp, charging devices overnight, etc.) even if the vehicle is parked and not running. The second battery usually charges off the main vehicle's alternator, alongside the main vehicle battery, when moving you are on the go. When stationary, the second battery is the one that drains down from all the various accessories, and a proper dual battery system will "isolate" the secondary battery from the main battery when stationary (Isolators, DC to DC chargers, etc. do this). Therefore, your main starting battery is not used for camp power needs.

Solution 2) If a dual battery is not in your budget or you don't have the space, that's OK -- lots of people run fridges off of a single battery. Just make sure the fridge you buy has built in voltage monitoring and shutoff. When the fridge detects that the battery is below a certain level, it will turn off automatically to prevent stranding you. HOWEVER, that only applies to the fridge -- if you also have stuff plugged in like lights, they won't have an auto-shut-off so you can still kill your battery that way. The other risk is that as a battery ages, it's ability to hold and discharge current often fades. With dual batteries, your starting battery is always staying pretty well 'charged'. With a brand new starter battery, you're probably fine to trust the auto-shutoff on your fridge. But as that battery ages, it may be more likely that the auto-shutoff doesn't happen in time to preserve your starting ability.

If you are only ever in populated spaces or camp with other rigs, you're probably fine. But if you are doing solo travel or really remote stuff, a proper dual battery system is a huge asset for having both camp electricity and peace of mind that you can get home again.

 

[Herbie]

Solution 2B) As above, some folks rely only on the Starter battery, but keep a small lithium "Jump Pack" on hand in case of any of the aforementioned issues.

I run Solution (1), but if I were going to try for a single-battery solution, I'd definitely keep a jump pack on hand...

 

[jdlobb]

Great question, jdlobb. Two answers, but the most direct to your thread title: They DO drain the battery.

Solution 1) Dual Battery system. Many folks fit these specifically to ensure that they can meet their 12V demands in camp (Fridge, lights in camp, charging devices overnight, etc.) even if the vehicle is parked and not running. The second battery usually charges off the main vehicle's alternator, alongside the main vehicle battery, when moving you are on the go. When stationary, the second battery is the one that drains down from all the various accessories, and a proper dual battery system will "isolate" the secondary battery from the main battery when stationary (Isolators, DC to DC chargers, etc. do this). Therefore, your main starting battery is not used for camp power needs.

Solution 2) If a dual battery is not in your budget or you don't have the space, that's OK -- lots of people run fridges off of a single battery. Just make sure the fridge you buy has built in voltage monitoring and shutoff. When the fridge detects that the battery is below a certain level, it will turn off automatically to prevent stranding you. HOWEVER, that only applies to the fridge -- if you also have stuff plugged in like lights, they won't have an auto-shut-off so you can still kill your battery that way. The other risk is that as a battery ages, it's ability to hold and discharge current often fades. With dual batteries, your starting battery is always staying pretty well 'charged'. With a brand new starter battery, you're probably fine to trust the auto-shutoff on your fridge. But as that battery ages, it may be more likely that the auto-shutoff doesn't happen in time to preserve your starting ability.

If you are only ever in populated spaces or camp with other rigs, you're probably fine. But if you are doing solo travel or really remote stuff, a proper dual battery system is a huge asset for having both camp electricity and peace of mind that you can get home again.

So assuming a fresh battery (I'm getting a brand new battery installed this saturday), how long can you actually run a fridge before it cuts off? With a mid-range fridge like the Indel B, is it safe for an entire day?

I do always have a jump pack in the car already.

 

[dreadlocks]

Solution 2B) As above, some folks rely only on the Starter battery, but keep a small lithium "Jump Pack" on hand in case of any of the aforementioned issues.

I run Solution (1), but if I were going to try for a single-battery solution, I'd definitely keep a jump pack on hand...

You should have a jump pack regardless of the fridge or not if Overlanding, not many people around to hook jumper leads up to..

However, starter batteries are not designed to be discharged deeply (ie, over 10% discharge).. they are made for high amp output with a ton of small cells in parallel, they tend to last pretty well if all it does is start an engine and instantly get a charge source.. but on the other hand, if you start deeply discharging it its going to fail prematurely, and if you struggle to get it fully charged (takes 7-8h of charge current on a discharged battery at max charge rate) its going to fail prematurely.

So assuming a fresh battery (I'm getting a brand new battery installed this saturday), how long can you actually run a fridge before it cuts off? With a mid-range fridge like the Indel B, is it safe for an entire day?

Most very efficient fridges use ~20AH per day, you cannot discharge a lead battery past 50% SOC and expect it to last more than a couple cycles.. so if you have a 100AH battery, its only 50AH usable, so just over 2 days with a very power efficient fridge, less with a less efficient fridge.. the numbers are dramatically variable, if its 150F in your truck parked in the sun you could get a day out of it, if its winter and 40 degrees all the time you could get 4-5 days out of it.

 

[Herbie]

You should have a jump pack regardless of the fridge or not if Overlanding, not many people around to hook jumper leads up to..

I agree. One of the reasons I run a 2-battery system (and built it the way I did) is to provide self-jump capability. My deep cycle AGM house battery (EastPenn/Deka 8A31DTM) is basically an 800CCA jump pack.

I do recognize that I have more than the minimum-necessary level of investment in this area, however.

 

[dreadlocks]

I do recognize that I have more than the minimum-necessary level of investment in this area, however.

lol, yeah me too.. 650W of solar, Lithium, and a Genset now days.. it all started off with a lil fridge about a decade ago.. that spiraled out into a very expensive setup, but hey I can finally boondock indefinitely w/out ever running out of power and that's not a very easy target to hit.. my first two attempts failed, learned the hard way you gotta plan for the worst and hope for the best, not the other way around.

 

[adaml]

So much of this depends on so many variables.

1. What fridge did you get?
2. Where do you store it?
3. What are the ambient temps?
4. What do you chill the fridge down to?
5. How full is the fridge?
6. How long is the vehicle sitting for?
7. How long is the vehicle running for?

Given how we use our truck and fridge, we never run down the battery because we're almost always exploring and we're generally stopped just for a quick lunch OR just for dinner/sleep/breakfast (a little over 12 hours at most). With those conditions, I've found a single AGM battery to meet my needs. I had to replace the stock battery in my 4Runner with an AGM to reliably tun my ARB 50 but the stock AGM battery in my Raptor has ran my Dometic 75 DZ without issue for over a year now. The only time it runs down is if it's hot outside and I leave the truck parked for a couple of days. My solution to that is to just run an extension cord out to the truck when I know it's going to sit (which is something you apparently can't do with the new Dometic fridges or else they may catch fire ...).

All that being said, most of these fridges should shut down when it detects battery voltage below a certain point. This will turn the fridge into an expensive cooler and hopefully allow you to still start your car

 

[dreadlocks]

All that being said, most of these fridges should shut down when it detects battery voltage below a certain point. This will turn the fridge into an expensive cooler and hopefully allow you to still start your car

Naw, all the low voltage disconnects I've seen on Fridges are set way too low.. they only kick in to stop you from completely destroying your battery by draining it down to 10v, you wont have much luck starting a vehicle with less than 12V.. 11.8V was highest my ARB fridge went IIRC, is only at 30% SOC, already dangerously under the 50% SOC you shoulda stopped at before hurting the battery.

 

[Thinman]

Can any of the external lithium batteries (jackery et al) be wired to both the car and solar for charging with it auto switching? I wanted to do a dual battery in my Jeep, but there are too many times I'll move to my truck for trips so something portable makes more sense for me. Would love to just plug everything in and forget about it with the lithium charging from car battery when available and solar when not, or both simultaneously if possible.

 

[adaml]

Naw, all the low voltage disconnects I've seen on Fridges are set way too low.. they only kick in to stop you from completely destroying your battery by draining it down to 10v, you wont have much luck starting a vehicle with less than 12V.. 11.8V was highest my ARB fridge went IIRC, is only at 30% SOC, already dangerously under the 50% SOC you shoulda stopped at before hurting the battery.

Interesting that you say that while both my ARB and Dometic fridges not only had a configurable cut-off but both of them, even left at their default "medium" setting, have successfully cut-off and allowed me to start my vehicle. Crazy!

 

[adaml]

Can any of the external lithium batteries (jackery et al) be wired to both the car and solar for charging with it auto switching? I wanted to do a dual battery in my Jeep, but there are too many times I'll move to my truck for trips so something portable makes more sense for me. Would love to just plug everything in and forget about it with the lithium charging from car battery when available and solar when not, or both simultaneously if possible.

With enough money, anything is possible ...

 

[dreadlocks]

Interesting that you say that while both my ARB and Dometic fridges not only had a configurable cut-off but both of them, even left at their default "medium" setting, have successfully cut-off and allowed me to start my vehicle. Crazy!

Wiring, the LVD is on the fridge side and not the battery side.. so under load it'll reach the low voltage cutoff before the battery is there.. that's the other problem w/fridges, them shutting off too early when you got a dedicated battery because you need ridiculously oversized wiring for a remote LVD to operate accurately (virtually zero voltage drop under load).. it can be highly subjective to your install, and it's unadvisable to rely on it to get your engine running and back out of the sticks.

 

[adaml]

Naw, all the low voltage disconnects I've seen on Fridges are set way too low.. they only kick in to stop you from completely destroying your battery by draining it down to 10v, you wont have much luck starting a vehicle with less than 12V.. 11.8V was highest my ARB fridge went IIRC, is only at 30% SOC, already dangerously under the 50% SOC you shoulda stopped at before hurting the battery.

Wiring, the LVD is on the fridge side and not the battery side.. so under load it'll reach the low voltage cutoff before the battery is there.. that's the other problem w/fridges, them shutting off too early when you got a dedicated battery because you need ridiculously oversized wiring for a remote LVD to operate accurately (virtually zero voltage drop under load).. it can be highly subjective to your install, and it's unadvisable to rely on it to get your engine running and back out of the sticks.

So wait a minute, they shut off too low and kill my battery or they shut off too early? Which is it?

I'm not saying you're wrong about any of this but I am saying that what I've seen and what I've personally experienced from two different fridges doesn't reconcile with what you're saying.

My ARB in my 4Runner drained the stock battery to 11.something and the truck would still start fine (if a little slow). I changed to an AGM battery and never had a problem. The Dometic in my Raptor shuts off as well after draining the battery to 11.5 (according to the truck) and it still starts just fine.

 

[dreadlocks]

your wiring is inadequate, so its shutting off at a higher voltage than you set it at.. you didn't seem to do it intentionally, so your personal experience is largely irrelevant as its not a universal truth that everyone here is going to use your gauge and length of wiring with similar loads, if they put in adequate wiring the'll have the opposite experience.

I'm glad its working for you, but the advice to let the LVD do its thing so you can still start up is rather poor and dangerous.