proper battery capacity

[gothicsurf]

Currently working on a truck camper conversion so I can head out and not have to return to or continue paying for a home base. In the way of a battery I am looking at using a single deep cycle SLA battery that I can simply hook directly to the starter battery/alternator. I would like to know if I am missing any details and what people think of these Mighty Max batteries I found at Home Depot.

I have one 100Ah and one 110Ah -- the larger is only ~7lbs heavier but seems a bit too large. It has 5/16" bolts for the terminals while the other has 1/4. I plan on having a small compressor fridge, some leds, couple fans, an ebike charger, laptop, etc. Curious what other people would do with these constraints and if they would opt for one or the other of these batteries.

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[Sofisintown]

If you hook up your 'house' battery directly on the starting battery, you will discharge them both every time you use electricity.
Unless you run the truck day-in and day-out, it it a matter of -short- time before you will kill your starting battery, and you are going nowhere.
Starting battery and deep cycle are two different animals. The truck battery can not take deep discharge without being damaged.
You need an isolator to make sure your house battery will not kill the starting battery if that's the only way you have to charge the house battery.
Think solar.

 

[highdesertranger]

using your vehicles alternator for supplemental charging is a great idea but using it as your only charge source is a poor idea.

I don't think you realize how long it takes to recharge a deeply discharged battery. you would need to drive 5-8 hours at highway speed each and everyday. read that again 5-8 hours EVERYDAY. this is why solar works so well.

is there a reason you left solar out?

highdesertranger

 

[gothicsurf]

Yes I do plan on hooking a simple relay/solenoid to the 12V lead from the ignition, so with the key turned to ACC the batteries are connected.

I forgot to mention that detail. Though before I build a container for the battery, I am still trying to decide on the capacity .. I have a feeling the two are designed for different uses, with different stud sizes and all. Guess for the larger I just need to find larger ring connectors and that could be the bulk of the difference?

 

[jacqueg]

If you hook up your 'house' battery directly on the starting battery, you will discharge them both every time you use electricity.
Unless you run the truck day-in and day-out, it it a matter of  -short- time before you will kill your starting battery, and you are going nowhere.
Starting  battery and deep cycle are two different animals. The truck battery can not take deep discharge without being damaged.
You need an isolator to make sure your house battery will not kill the starting battery if that's the only way you have to charge the house battery.
Think solar.

Yup. Also, charging the house battery from the starting [font=Tahoma, Verdana, Arial, sans-serif]battery[/font] is VERY slow. You won't keep that house battery charged enough to run a fridge unless you drive for hours every day. Ask me how I know!

You will need a small generator or solar to run a fridge. Or you can decide to not run a fridge. With careful management, you can keep USB gadgets, such as a light and your phone, charged from your starter battery.

But the FIRST thing you need to do is get a calculator and figure out how much battery capacity you need to run everything you want to run. This is essential information, and you MUST learn how to figure it out, as it will change every time you add or subract something from your system.

Otherwise, you are just setting yourself up for endless frustration.

Start here to figure out what size battery you need -  This vid also includes how much solar you will need to feed that house battery. But your first step is understanding what your battery capacity will need to be.

 

[Spaceman Spiff]

Currently working on a truck camper conversion so I can head out and not have to return to or continue paying for a home base. In the way of a battery I am looking at using a single deep cycle SLA battery that I can simply hook directly to the starter battery/alternator. I would like to know if I am missing any details  . . .

You are starting out backwards.

You first want to add up all the energy you will use in a day.  That determines the minimum amount of battery you need (you need at least twice the capacity with lead-acid).

Then you will need to determine how much you will need to drive to refill the battery(s) every day, keeping in mind that to get from 80% to 100% takes a minimum  of 2 hours (usually more like 3).

There are automatic charge controllers, solenoids, and DC to DC chargers that will separate the starter battery from the house battery so you don't drain the starter battery.  But unless you have a need to drive for 3-4 hours a day you will find that alternator charging is not cost effective.

 

[tx2sturgis]

Your e-bike charger will pull a fair amount of amperage from a house battery, assuming you ride the thing and need to charge it every day or two.

Your compressor fridge will be a constant draw on the one battery, so, two would be better. 

Why not hook up both in parallel, the capacities are close enough to be compatible, and then use either a 'smart' isolator, b2b charger, or a solenoid, AND ~200 watts of solar to keep them fully charged. 

Several choices, several solutions. Depending on your budget and preferences, and also how much time you will spend driving, vs sitting in one spot, will influence those choices.

 

[gothicsurf]

I forgot to mention there will be 200W of solar on the roof. I definitely would not want to have to drive to keep the battery topped off. The fridge is not constant but off and on, but that is really the only mandatory draw, think it's 3.5A when running. The others are auxiliary and can be sacrificed to keep the fridge contents chilled.

The ebike battery charger is likely through an inverter and just got to thinking it would be proper to have a low voltage cutout for the 110v set somewhere higher than that of the rest of the system. Probably going with a 500W inverter but don't think any in this range have an adjustable cutout.

Anyway just started this thread because I can't chose between these two batteries ..

 

[RvNaut]

Anyway just started this thread because I can't chose between these two batteries ..

Go for the larger capacity... and then wish you had bought more

... as others have said.. you might find that one battery cannot keep you powered up...

Will Prowse - Solar geek..

 

[barleyguy]

Do you not have room (or weight) for both batteries? Since those are the same chemistry and so close in capacity, you could hook them both up in parallel and keep them both.

With 200 watts of solar, you want about 200 amp hours of battery, as a rule of thumb. That's basically exactly what you've got.

 

[gothicsurf]

My thinking was to steer for fairly minimal energy use to keep just one of these batteries topped off with solar. I am definitely looking to take the shadows out of the equation and wire them in parallel with a PWM so any shadow on one would have minimal effect on the other. All energy use willingly sacrificed to keep the fridge going and the battery topped off. In this case battery capacity may not need to be maximized?

 

[barleyguy]

My thinking was to steer for fairly minimal energy use to keep just one of these batteries topped off with solar. I am definitely looking to take the shadows out of the equation and wire them in parallel with a PWM so any shadow on one would have minimal effect on the other. All energy use willingly sacrificed to keep the fridge going and the battery topped off. In this case battery capacity may not need to be maximized?

The primary reasons for larger battery capacity are:
1. To make it through the winter months. In December you'll only get about 3 times your panel rating per day, i.e. 3 sun hours.
2. To make it through cloudy days without running a generator. If you have a few days worth of storage, you can make it through a few days of rain.

 

[B and C]

I don't recall anyone saying they wish they had less battery capacity or less solar.