CCA vs discharge rate for SLAs

[gothicsurf]

I am currently outfitting my truck with an SLA/AGM battery as an auxiliary to the starter. The specific model in mind is the Mighty Max 110Ah battery widely available. It will be connected to a solar charge controller and two 100W panels as well as to the alternator/starter through a solenoid isolator circuit. I plan on using it mainly to keep a 12V compressor fridge below 40-45 deg F during the day, while at night switching it off. The fridge has a low voltage cut out at 10.5V, but might like to put an additional relay at 11V just to prolong the battery. The draw is about 3A when on which is only intermittent depending on ambient temps. Although the panels will be mounted flat, I am fairly confident 200W are capable of keeping the battery fairly topped off.

• In attempt to have battery capacity capable of carrying it through stretches of multiple cloudy days with less of a dip. Given this 20L fridge is the only major draw, does 110Ah sound like sufficient reserve, or would something larger toward 125 or even 200Ah+ be better advised? (I know more battery capacity is never a bad idea, but would also prefer to minimize weight and design a system that keeps the charge controller close to the float stage).

• Regarding discharge rate, ideally the auxiliary battery can assist the starter in case the later reaches the end of its life or some other drain occurs. However, this SLA fully charged to 13V connected to the starter circuit with the starter battery disconnected and was not able to turn the engine. I looked up the spec sheet and saw the max discharge rate at 900A, which seems to be ample relative to a 550 CCA starter battery. Are these two figures are comparable, and if so, can I expect the SLA to turn over the engine, or perhaps the battery integrity should be suspected?
  

     

 

[Weight]

You need at least one set of golf cart 6 volt batteries. Wet cell. that is 230 amp hours. So match the other batteries to that.

 

[bullfrog]

What type of vehicle is this battery trying to turn over?

 

[jonyjoe303]

The mightymax should have cranked over your starter, it has 900cca, more then enough. Maybe the wiring your using isn't heavy gauge enough. Did you get the starter to click like it has a low battery? is the solonoid turning on?

On my van I had several incidents where over a long weekend the start battery would barely crank me over. I installed a small 27ah agm as a start battery but even that battery also was giving a slow crank. What I did was build a 2 amp charger and every morning before I start the van I turned the charger on ( connected through cigarette lighter). The charger tops off the battery to 14.7 volts which is what the agm needs. I get a powerful start every time.

The 110ah battery should easily keep your fridge at 40f, you might not even need to unplug the fridge at night. I got my fridge set to 16f and it uses about 20 ah in 24 hours. Years ago I use to keep my 43 quart fridge at 40f with a 75ah agm and 120watt panel, I never unplugged it. If the battery gets too low, the fridge stops working but still keeps your food cold all night long. On my fridge I hotglued 3 layers of foam insulation around the sides of the fridge to make it more efficient at the lower temperatures I like. I'm sure it will work on your fridge if you need more power efficiency.

 

[gothicsurf]

What type of vehicle is this battery trying to turn over?

4 cyl toyota pickup

The mightymax should have cranked over your starter, it has 900cca, more then enough. Maybe the wiring your using isn't heavy gauge enough. Did you get the starter to click like it has a low battery? is the solonoid turning on ..?

At hand was a set of jumper cables which are pretty heavy gauge.

27ah seems quite small for a starter .. was it somehow a high dischage chemistry?

Should I let the fridge discharge my battery all the way to the 10.5V cut off?

Wonder if I should be concerned about a 900A battery that can't turn an engine (might have turned one rev but then started clicking) -- sure max discharge equates to CCA? The chemistry of a flooded battery just might have more 'torque'? Why a 2A charger rather than connecting the batteries directly with a switch?

Thanks for your experience with capacity in relation to a fridge/solar setup.

 

[jonyjoe303]

The 27ah agm is a 8 year old fullriver fullthrottle agm, its small its comparable to the oddyssey brand, I used it to replace my interstate fullsize start battery that refuse to crank me over twice. The 27ah was installed only as a temporary measure 6 months ago, but it has worked extremely well. As long as I top it off with the 2 amp charger every once in a while it has never refuse to give me a powerful start. To top off the battery to 14.7 volts takes maybe 20 minutes and uses less then 1/2 amp from my house battery, thats why a 2 amp dc charger is all I need. I would recommend it to everyone as a way to always have a start battery fully charged ready to go, some alternators might not put out the full 14.4 volts some batteries need. I tried connecting the house battery directly (no dc charger) to the agm start battery and left connected all night but I still get slow starts, I found out the agm needs to be topped off to 14.7 volts for the best performance and as per the mfg they were correct.

And now that you mention using fullsize jumper cables, I always carried the fullriver for years for an emergency for jumpstarts in a small carrying case and have had to use it to try and jumpstart a v8 carburated impala just using the jumper cables, it easily crank over the v8, it wouldn't start after many tries because of a fuel problem. I'm very surprise your larger 900cca agm wouldn't crank over your 4 cylinder with the heavy gauge jumper cables. In comparison my fullriver only has 410 cca.

When you mentioned you heard the starter clicking, that points to a weak battery. I suspect maybe your mightymax was not fully charged. Years ago when I used a 102ah kinitek high performance agm battery as a house battery, I discovered I was not fully charging it from my solar system, Due to voltage drop the battery wasn't even reaching 14.0 volts, over time undecharging the battery will cause it to lose capacity. Using light loads is no big deal but when you try running a heavy load like jumpstarting, its when you find out you got a weak battery. While charging from the solenoid or solar, measure the battery voltage from the terminals, you should see at least 14.4 volts. Anything less while charging and it might not be reaching a full charge.

I wouldn't let your agm discharged below 12.1 volts, but a fully charge 110ah agm will easily run your fridge several days/weeks/months before reaching 12.1 volts if its top off on solar every day. But once you see 12 volts on your battery you can unplug the fridge. The only time my fridge stop running from low battery was during cloudy conditions and the battery wasn't being topped off. Back then I would just let it run below 11 volts but since then have learned its very bad for a battery to go below 12 volts.

fullriver fullthrottle 27ah agm, I use as a start battery on my 6 cyl astrovan.

 

[gothicsurf]

As you allude to, maybe the AGM/SLA type of battery has difficulty providing enough current to a starter while at a mere 13V? If this is the case, suppose mine may be performing normally -- I wonder what the manufacturer would say .. seems like a voltage boost from such a charger as you mention may the way to go.

What I did was put the Mighty Max on a generic 2A lead acid car battery charger over night, disconnected it and saw the voltage stabilize to roughly 13.0-13.1V.

What I did was build a 2 amp charger and every morning before I start the van I turned the charger on ( connected through cigarette lighter).

Maybe you can recommend a good simple 12V --> 12V (14V) charger that I could connect to my SLA with a switch for an emergency backup?
Also, what is your house battery? Is it also something approaching a discharge current ≥550A?

I wouldn't let your agm discharged below 12.1 volts, but a fully charge 110ah agm will easily run your fridge several days/weeks/months before reaching 12.1 volts if its top off on solar every day. But once you see 12 volts on your battery you can unplug the fridge. The only time my fridge stop running from low battery was during cloudy conditions and the battery wasn't being topped off. Back then I would just let it run below 11 volts but since then have learned its very bad for a battery to go below 12 volts.

Well, I could see how staying ≥12V for a flooded battery would be safe, but this seems bit wimpy for deep cycle. Aren't they supposed to be capable of at least a 20-30% drop without major deleterious effect?

 

[jonyjoe303]

The expensive/heavy deep cycle agms can handle going all the way to 10 volts. Oddesey claim there agms can be drain that low 100's of time before they lose capacity but those are expensive, a 16ah oddesey agm cost almost 120 dollars. I bought one of the 16ah oddesey to use as an emergency jump start battery but haven't used it yet, its a beautiful battery. In an emergency I can use it to jumpstart the engine with jumper cables or even use it as a start battery, it has the top/sidepost mounts.

Lead acid batteries, once they start losing capacity, they will quickly charge to full and will even show good voltage but as soon as you put a heavy load on it, the voltage will sag tremendously. If the 2 amp charger your using or solar panel is quickly going to float mode, then the battery might have lost capacity. My kinitek was reading 12.9 volts after charging all day with solar but it couldnt handle running a laptop for too long once it started going bad. The kinitek was suppose to be a high quality agm but I drained it below 11 volts about 3 times when it finally lost full capacity, after that it only had enough capacity to run my laptop about 3 hours before the inverter quit.

If you have a dc wattmeter, fully charge your battery, then discharge it through the dc wattmeter it will track how much amps you are using, when the battery reaches 12.1 volts, check how many amps you used. You should have used 55 amps to get to 12.1 volts. If you only use 30 amps or less when you reached 12.1 volts then your battery has lost capacity.

My house battery is a 220ah lifepo4, it maxes out at discharge current of 30 amps. It only charges from my 240 watt solar panel. The only connection to the start battery is from a 2 amp dc charger that is connected to the dash cigarette plug. The dc charger I built myself using a 5 dollar boost converter and a 5 dollar buck converter. Thats the only way I could charge from the house battery to the start battery using the exact voltage/amp I wanted. A dc charger like mine would come in handy if you park for several days without running your engine.

 

[gothicsurf]

Suppose there are any car chargers with a 12V input commercially available?

 

[theBest]

What Is The Difference Between A Solar System Battery And A Normal Battery?

Batteries have a lot of properties. For example, some batteries need to be fully discharged before charging. Some batteries (car starter batteries) are designed for supplying short bursts of high current and then be recharged and are not designed for a deep discharge. Usually the "usual" battery is a plain old car starter battery and the "solar" battery is a deep-cycle lead-acid battery which is more or less a variation of a car starter battery.

https://electronics.stackexchange.c...n-a-solar-system-battery-and-a-normal-battery

Batteries for Storing your Solar Power

What is a deep cycle cell? Deep cycle refers to the fact that in a solar power system, it is likely that the battery will become charged during a sunny day, then they may become almost fully discharged with use, before they are again fully charged.
On the other hand, a car or truck battery is not designed for this type of use. Although the starter motor of the vehicle will draw a considderable amount of current from the battery, it will nowhere near fully discharge it (unless the vehicle fails to start and the driver continues using the starter motor for some time). The car or truck battery is therefor designed to be used virtually fully charged all of the time.

https://www.solar-facts.com/batteries/

Two other types are also available, both of which may be termed a sealed lead acid battery though they do have a pressure relief valve:

Absorbed Glass Mat (AGM) - where the electrolyte is absorbed in a fine fibreglass mat between the electrodes
Gel - where the electrolyte is in the form of a gel.

Both the above types of battery can withstand being turned over without spilling electrolyte and therefore have specific uses.

Due to these batteries being at least semi sealed, care has to be taken to ensure that no excessive gassing occurs (which occurs at higher charging voltages). Therefore these batteries may require a specific charge controller. Charging with the wrong type of controller can cause an explosion.

https://www.solar-facts.com/batteries/battery-types.php