DC Load on Shore Power

kevman

Observer
This is probably a silly question but I've searched a bunch and haven't found much information. (Which usually confirms the silliness.)

Anyway, what is the impact that a DC load can have on the battery while connected to shore power? Do small discharges have an affect on the batteries life? For example, if I had a DC fridge that I wanted to keep on while plugged in at home between trips would this cycling lead to premature battery wear? If the fridge draw was ~2% of the battery bank (4A fridge/200Ah battery) would the charger float stage take care of this draw? If not, the battery would occasionally drop below the voltage cut off and my charger could go back into bulk stage and start another cycle. I've seen cycle life specifications for 30% vs 50% vs 70% depth of discharge but nobody ever mention 5%. Is this because such a small depth of discharge has very little influence on the life of a battery?

Long story short, I'm buying a new fridge and am torn between DC only and AC/DC. The only time I'd ever use AC is plugged in at home between trips when I'd like to keep the fridge on. However if there is no real risk to the battery by running it off DC while on shore power I can save a bit of money by getting the DC only version.
 
This is probably a silly question but I've searched a bunch and haven't found much information. (Which usually confirms the silliness.)

Anyway, what is the impact that a DC load can have on the battery while connected to shore power? Do small discharges have an affect on the batteries life? For example, if I had a DC fridge that I wanted to keep on while plugged in at home between trips would this cycling lead to premature battery wear? If the fridge draw was ~2% of the battery bank (4A fridge/200Ah battery) would the charger float stage take care of this draw? If not, the battery would occasionally drop below the voltage cut off and my charger could go back into bulk stage and start another cycle. I've seen cycle life specifications for 30% vs 50% vs 70% depth of discharge but nobody ever mention 5%. Is this because such a small depth of discharge has very little influence on the life of a battery?

Long story short, I'm buying a new fridge and am torn between DC only and AC/DC. The only time I'd ever use AC is plugged in at home between trips when I'd like to keep the fridge on. However if there is no real risk to the battery by running it off DC while on shore power I can save a bit of money by getting the DC only version.
First of all, I never think a question such as this could be silly. Understanding the technology that we have around us in this Modern Life is a challenge for anyone. Things change very quickly and we're so flooded with information, we can't possibly keep up with all of the evolution going on. The good thing is, that we are never bored if we want to stay up to speed with all of the technological advancements going on around us, right? And all of these changes create new personal and business opportunities.

And so, in regards to your question, it is a very good question actually. I'd say the short answer is depends on the type of battery that you are using to power the fridge. I would not recommend using a starter type battery. I would recommend using a deep-cycle type battery. In addition, I would spend the extra money for an AGM or GEL type. They are designed for this type of cycling: a slow discharge and a slow recharge. Their large plates and closed chambers are efficient at delivering energy when needed and recuperating with minimal change to their structure. Yes they cost alot more, but they will last a lot longer, they are truly maintenance-free, and I have put them through some brutal regimens with amazing positive results.

Regards,
RestorationRides

Sent from my Z981 using Tapatalk
 

DaveInDenver

Middle Income Semi-Redneck
The short answer is yes, any cycling is consuming life from the battery. But a battery is also slowly dying doing absolutely nothing other than self discharging or even just sitting on an ideal float charge. So the question is really how do you best maximize the life of a battery. To do that you want to use a good charger that monitors the battery, cycles it through a periodic equalization and is sized sufficiently that when the fridge does cycle it has enough excess capacity that it supplies the current and the battery doesn't. If a battery is sitting there floating with a small trickle and a charger/supply is perhaps capable of 15A then when a load of 5A or 10A turns on the battery doesn't even notice. That situation can be left indefinitely. It's essentially the concept behind a UPS. Those batteries usually die from *not* being cycled and/or allowed to overheat.
 

john61ct

Adventurer
As long as the charge source is putting out greater current than the consumers are pulling, the battery won't be touched.

If course the amps actually available to charge the bank will be reduced, but once past the 80-85% it is accepting lower amps anyway.

All this is easily verified with a couple strategically placed ammeters, or AH counters for logging over time.
 

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