Swapable heavy battery pack

Community General Discussions
1

I am designing a piece of equipment which will make use of two 12v Lead-Acid battery packs to provide 35 Amp-Hrs at 24v.  They are AGM type, because the equipment will be expected to rotate 180 deg.  The batteries are heavy, and I will use two of them to get 24v.  So, that is over 40 Lbs.

While I expect the battery to last all day, I would prefer to permit the users to easily swap out a weak battery pack for a fresh one. I first thought of mobility battery packs, but those are not designed for mounting on rotating.

Does anyone know of an existing design for a quickly-swapable battery pack that can be attached to equipment that rotates 180 deg, and can handle 40 lbs of battery?

-Joe

2

Just curious

Is your design “set in stone”?

Just curious why you are going with the heaviest and most inefficient battery technology available?

3

The design is still

The design is still flexable.

The reason I chose Lead-Acid is that it is cheaper and electrically more robust that other technologies. It also gives a more predictable 'battery fuel gauge" becase the voltage decreases in a predictable way as the battery is depleted.

Its main negative, for many applications, is its weight.  But, this is for a piece of equipment that is already fairly heavy anyway. So, the weight is not a significant factor.  

I imagine that for many mobility scooter’s the weght is even an advangage, since it provides ballast to help keep the chair upright.

Old technology can be better than new technologies in some circumstances.

-Joe

4

Batteries

Both Li-Ion and NiMh are very mature technologies and both offer significient power/weight improvement over gell cells. They also offer much longer life, (more charge / recharge cycles), than gell cell. By the time a typical gell cell is 2 years old, it is shot. I have Li-Ion & NiMh batteries that are over 10 years old and still plugging away. Battery monitoring, (fuel gauge), is simple with either technology and the Li-Ion have built-in monitoring making it even easier.

5

Batteries

I’m very familiar with AGM batteries as that is what I use in my motorhome. I’m not sure where you’re getting your data on car batteries, even when well maintained, they seldom last 3 years. I’ve lived in Ohio, Kentucky, California, and now Arizona and I would be thrilled, (and very surprised) to get even 5 years out of a car battery regardless of the brand or price. Here in Arizona, 2 years is average life. The battery can be perfectly fine when you start the car to go to the store and when you try to start it to come home, nothing, not even a click, absolutely nothing.

Good luck with your project.

6

I just looked up some car

I just looked up some car batteries to see what their replacement warranty is.  Their standard batteries have a 2-year replacment warranty, and 72 month pro-rated warranty period.  Warranties are typically longer than the actual life of the product.

So, I am thinking that your own 3-year experience is not typical.  It certainly is not my experience.  

There are a number of ways Lead-Acid batteries can have shortened life. Though, your 4-state experience should eliminate some of them. And you have enough battery knowledge to know how to maintain them properly.

If you are having such a bad experience with Lead-Acid, why are you using them in your motorhome?

-Joe

 

7

The batteries I am using are

The batteries I am using are actually AGM (Absorbed Glass Matt), which is similar to Gel, in that it can be used in sealed Lead-Acid batteries, but AGM is much more tolerant of fast charging, and has other advantages. The true Gel-cell is not used very much any more from what I have read.

Your 2-year life on you Lead-Acid battery is only because it was not properly charged and/or maintained.  Car batteries regularly last over 10 years, and I read one gentleman talk about 25 year old lead-acid industrial batteries.

The Li-Ion & NiMh batteries you talk about are less robust, but generally have some smart electronics installed that work to make sure they are charged/discharged properly.  So, that is how they can last so long.  But, both the underlying battery type, and the smart electronics to keep them in shape cost more money.  

But, at your prompting, I did a little more research.  I see now that the Li-Ion batteries can be discharged to a greater percent, and have about a 20% greater usable capcity over lead-acid.  So, for the same usable energy, the price disadvantage that Lead-Acid has is reduced.   Though, they still are significantly more costly.  The Li-Ion will have a longer life, especially in the South Florida weather weather where this equipment will be used.  So, over the long term, the price comparison may start to converge.

But, in my application, the equipment is a prototype, and is subject to being changed. The Lead-Acid AGM type battery is still the clear winner.  

In general, if something more efficient or better in the long term, but more expensive, does not pay for itself within 2 years, it is probably not worth the investment.  This is because the equipment itself may be abandoned, replaced, or sold. The expensive batteries may get damaged. So, it is easy for any long-term advantage to become a liability.

As an aside,  I have seen alternative-energy ideas that propose a 10-year payback (even with government subsidies)… those people are fooling themselves.  Aside from the fact that the efficiencies touted tend to be overblown, and maintenance/repair costs underestimated, a 10 year payback time is of no real value. They are a gamble with the odds stacked against you.

-Joe

 

 

8

Batteries

Joe, I Googled, “How long should a car battery last?” and here are the typical answers:

The life of your car battery depends on how long it can hold its charge, and is capable of being recharged. Once it can’t be recharged, it’s dead. There are a number of factors that can affect your car battery, including humidity, temperature, and other environmental factors.

Let’s assume ideal conditions: no high temperatures, no excessive humidity – in short, a perfect world for your car. Under these conditions, you can probably expect your car battery life to be about six years. On average, a car battery lasts between two and five years. If you live in the northern United States, your car battery lifespan will be longer, because you’re in a cold climate. Warm climates tend to increase damage due to sulfation and water loss.

Good care extends battery life

Of course, proper car battery care can greatly enhance your car battery lifespan, and the best way to make sure that your car battery lasts a long time is to always keep it fully charged. That means that you should try not to leave your lights on or leave accessories plugged in. Also, make sure that your battery is always checked during routine vehicle maintenance.

Your battery life depends on these two main factors: where you live and how well you take care of the battery. If properly cared for, however, you should get a number of years out of your battery, assuming that you own a gasoline powered or diesel fueled vehicle. If you own a hybrid, or an electric car, you can expect to get an amazing eight years of auto battery life before you have to think about replacing it

Then I searched on “How long should a car battery last in Arizona?”.

 

Talked to the navigator guy, he says he replaces the battery on his Mercedes 350 something every 2 years due to the heat of summers. I wow’d… I used to think Mercedes and BMW batteries live for decades! Turns out not in every climate? Or not. What’s your experience?
Yep, my Volvo eats a battery about every 2 years.  Even a good, high end battery.
Yep, about two years. Same goes for batteries in your car, like garage door openers. The heat does a number on them.
Pay full price one time and then pay pro-rated amount upon replacement every 2 years.
Yes I have to replace mine every 2 years. They say that heat is worse on cars then the cold which surprises me. I lived in the frozen tundra in WI for 25 years before I moved to AZ and I had never replaced a car battery before.
Sorry to burst your bubble, Albert, but the battery in my XC70 is in my trunk (behind an access panel) and I use Interstate Brand…still get about 2 years.
Give or take, I did go a few months over 2 years once.  Felt like I was living on borrowed time too, lol…
My car batteries always die the month AFTER the free replacement part of the warranty has expired, so I always have to pay the pro-rated amount. Sigh.
Yep, my mechanic says average battery life here is 22 months.
Joe, there were lots more of the same or similar so it appears my experience with batteries is more typical than yours is.
9

I see. I am in

I see.  I am in Pennsylvania, so that clearly helps battery life.

You didn’t answer the question about your motor home.  Why lead acid and not Li-Ion?

-Joe

10

By the way, about the 25

By the way, about the 25 year Lead-Acid I was refering to.  This was for a stationary industrial application.  But, in this case, the battery did get some re-furbishing every few years.  I forgot the details, but the lead plates themselves was left as it was.  

-Joe

11

Motorhome batteries

I can’t use anything but lead acid in the motorhome, that’s what the electronics are designed for. There is a charger that operates anytime there is A/C plus I have about 250 watts of solar on the roof with it’s own charge controller. To convert to another battery technology would mean replacing all the electronics.

12

Electric car batteries

Joe, I forgot to mention, the Nisson Leaf, (electric car), will not honor the battery warranty if you live in Arizona.