24 Volt System - Input/Advice - updated 6/19/15

[dwh]

Your math looks good so far. 192ah worst case.

So..what's the question?

 

[jeepboy_90]

Just making sure I was on the right path.

Two AGM batteries at 100 Ah it is.

Thanks

 

[dwh]

Two AGM batteries at 100 Ah it is.

Rigged in series to get 24v, it will be a 100ah bank, so it would only supply half of your worst case scenario - and that would be taking it down to fully dead, which will shorten battery life. Even double the battery bank would only supply your worst case if you took the bank all the way down.

To get 200ah and still only take the bank down to no less than 50%, you'd need 8 of those batteries rigged in 4 series strings and then parallel the strings.

 

[Simonblyth]

Hi

Following with great interest - I've just bought a 1964 Renault Goelette R2087 ex army ambulance which runs @ 24V which I'm converting to a 4x4 camper van

 

[redneck44]

Coming from a marine perspective, 24v is fairly common.
Work on 20% maximum discharge of your battery bank, to maximise your battery life. Discharging more than 20% really shortens your battery life.
Wire sizing is worked out by minimising voltage drop, 3% voltage drop is what I aim for, 10% max on non critical systems. Similar to DWH but approached from the other end.
As stated 2x 100amp batteries in series gives you 100amps
Your estimated consumption figures look a littlee high, why would you be running you inverter for so long?

Also consider your charging system from the alternator, and don't forget your solar input.

 

[dwh]

No one spotted the pop quiz error, so here it is...

You have to figure the load at whatever the inverter's lowest operating voltage is. So let's say it shuts down at a voltage of 10.5v. That would be 400w / 10.5v = 38a. If it shuts down at 11v - 400w / 11v = 36a. Shutdown at 11.5v - 400 w/ 11.5v = 35a.

But that's a bit deceptive. The fully charged battery will be resting at 12.8v, and if the inverter disconnects at say 10.5v, then we have to do TWO voltage drop calculations to know what's really going on - one at 12.8v, and another at 10.5v:

I got the 35a number by using an inverter shutdown voltage of 11.5v, but then when I did the voltage drop calcs, I used 10.5v instead and should have done the voltage drop calcs using 38a for the load instead of 35a.

Like I said, not enough of an error to invalidate the results - but it's still wrong. Okay for ballparking, but never would have passed my examiner when I was an apprentice.

Gotcha.

 

[jeepboy_90]

Still working on building out the rear of the Volvo.

I have the opportunity to get two (2) Deka DP31CS Batteries for FREE.

Could I use these for the house batteries for the time being?

Thank you

 

[dwh]

Those are cranking batteries. They won't last long being used for deep cycling.

 

[Antichrist]

I have a military vehicle that currently is setup with 24v. I am planning on keeping it that way, as all items are 24v already, including the LED's, accessories, etc.

Certainly doable keeping it 24v as this thread shows, but I wonder where you'll be traveling and the implications to your trip if a critical 24v component dies, like starter, alternator or fuel pump (if electric).

 

[unseenone]

That's a heavy duty commercial / severe service dual purpose battery. -- I like Deka batteries... Weight 57LBS 185Ah-- it sounds right up your ally.

I don't think it was mentioned previously in the thread. The 24V solar panel is mandatory, I do not think you can charge a 24v battery with a 12v panel, unless you run two as planned. I like Grape Solar, worth a look as well. I'm also thinking you may need about twice the solar to charge all 4 batteries efficiently.

The MPPT controller gives off a LOT of RF, so the original PWM PS-30M would be the best choice, it works and does not cause interference.

If you plan to run a ham radio, or something else that requires 12V you will need something like a Vanner 24-12V equalizer and an additional 12v battery for that. You may want to factor that wiring in while you are at it.

 

[dwh]

That's a heavy duty commercial / severe service dual purpose battery. -- I like Deka batteries... Weight 57LBS 185Ah

According to the product brochure, it's a cranking battery designed for delivery trucks - i.e., lots of starts and stops. Quick discharge, quick recovery, enough reserve capacity to keep the radio and flashers running while the engine is shut down.

And that 185 number is minutes reserve capacity - not amp*hours:

http://www.eastpennmanufacturing.co...ial-Cycle-Service_Dual-Purpose-Flyer-0213.pdf



It's a good battery - for what it's designed to do.

 

[jeepboy_90]

dwh - Thanks for the input on the battery, I figured free it would be worth asking.

Others - Thank you for the input. The rigs solar is designed for 24v and the MPPT is already in place. I have not had any issue with RF yet, during my trial setup. As for spare parts, a quick trip to Sweden would fix it. Spare parts are hard to come by and most trips will be no longer than a week at this point. I also have a 24v to 12v convertor for the vehicle.

 

[jeepboy_90]

Progress...

So I have had a week to put some work into the vehicle. Pictures coming soon.

Question of the day -
Solar panels are hooked up for 24v operation. When testing the output, they are showing 40.4v prior to the controller. However 0 amps? Am I missing something. In direct sunlight middle of the day.

Thanks...

 

[LeishaShannon]

How are you testing the output? 40.4v sounds like the open circuit voltage and you've stuck a multimeter across -ve and +ve? if you short the -ve and +ve through the "current" input on your meter you should see amps. (Make sure your meter can handle the expected current or you'll blow the fuse) Most meters can only handle ~10A

 

[jeepboy_90]

What I did was place the positive (red) and negative (black) from the multimeter to the positive and negative from the solar panels. This is not correct?