Battery Pack Questions - Slightly OT

[JohnnieB]

I screwed up royally in my calculation and somehow mixed up Run-time in minutes with AH storage capacity, so my guesstimate was way off the mark.

Trojan only publishes Run-time for T-105 batteries at 25A (447 Minutes) and at 75A (115 Minutes), but US Battery publishes a chart for their batteries at discharge rates from 5A to 125A and the US2200 (6V-232AH - circled on attached chart) has the same Run-time as the T-105 (6V-225AH) at the 25A and 75A discharge rates, so believe the Run-time at the 125A discharge rate (61 Minutes) would be about the same for the T-105.

The Run-time for batteries in series is the same as it is for a single battery, just the voltage is increased, however the Run-time in parallel adds and you have three set of two in series connected in parallel, so the effective Run-time with a 125A amp draw would be about 183 Minutes, or three hours. If you limit the discharge to 50% of storage capacity, you'll have about an hour and a half of Run-time at 125A discharge rate, and a lot longer at a lower discharge rate.

Check the labels, but I suspect the small coffee maker has a higher amp draw than the 600W microwave. In any case, you ought to be fine running them both off the inverter, maybe not both at the same time, but that is limited by the inverter rather than the battery pack.

I also attached a clean copy of the chart for anyone that wants it.

[coosa]

JohnnieB, many thanks for figuring all that out for me. I had the chance to some real world testing this weekend. We had Thanksgiving at my home, and then Friday my wife, daughter, son in law and grandson all went to the cabin to spend a couple nights.
I carried some cables left over from previous carts and wired up all the batteries with them, and then wired in the new 1500 watt inverter. We were gonna cook steaks on the grill Friday night, but nobody was very hungry so they decided to all fix plates and warm them with the microwave. I had never really anticipated using it this much at one time, and first thought of running it to the generator. But I decided to put it to the test and we heated 4 plates at 3 minutes each, so 12 minutes of running time.

Keep in mind I don't have the new battery pack yet. I have a mixed up set of 4 different 12 volt batteries now. Two of them are 105 amp deep cycle marine that are 4 years old. They are inside the house where it's heated. A cable runs outside the house to a bulldozer battery and a 75 amp marine battery. I frequently pull the small one off the line and use it for other tasks around the farm, then hook it back up when I leave. Nobody has to tell me this is a bad system. All of them need to be inside and they should all be the same size and age. But it's worked 4 years. One reason I've gotten by is I've only got 75 watts of solar power and it rarely shuts off. So anyway, this system is nowhere near as efficient as what I will soon have.

But it ran the microwave all 4 times and also made a pot of coffee. That took pack voltage from 12.7 to 12, so I had to fire up the generator and hook up a 10 amp charger I had brought. I never did get the voltage back to 12.7, and after a 20 degree night the inverter alarm came on when I made coffee this morning.

I think the system will work ok when I install the new batteries, and I'll add a few more solar panels too. I will also plug up the generator for using the microwave that much. Usually, it would be me warming one plate for myself and the inverter can handle that.

Thanks for all the help. I wanta post a pic of the batteries and get opinions on where to install them. And thanks to ScottyB for not zapping my ot thread. I do believe anyone with an electric cart should learn all they can about the batteries.

[coosa]

Here is a pic of that inside setup now:



The house is only a little over 500 sq ft, and this is the only place I have to put the batteries. A cable runs thru the floor and hooks to the other 2 batteries, but cold weather really reduces their efficiency.

My plan is to build a double shelf right over the spot where the 2 batteries are located, then put 2 on the floor as they are now, 2 on the first shelf just over them, and 2 on the second shelf just over them. I'll use 2x10 or 2x12 lumber, and leave a little space between the batteries and the wall. I'll have to move the junction box and buy a new charge controller. Then I plan to put a plywood door on the front of the entire shelf so that the batteries aren't seen at all. That will be a bit better aesthetically, but I am mainly thinking of safety. If a battery were to explode, the door should contain the acid so that it wouldn't get on anyone who happened to be in the room.

I know this isn't ideal, but the only other alternative is to put them all outside and lose a great deal of their capacity when its cold outside. I think this will be safe, but wondered if anyone disagrees? I've had 2 batteries explode in my life, and that's out of many, many hours of working with them. One was in a tractor and one was being charged in a shed. It blew holes in the batteries and splattered acid everywhere, but its not like its a stick of dynamite going off. I think its important to provide enough space around the batteries so that any vapor can move away from them, so I'm not talking about it being airtight. It wouldn't be significantly different than being in a golf cart.

I plan to mount some kind of battery charger on the outside wall. I have mentioned a 3 bank marine charger, but after using a regular charger as a backup this weekend I'm thinking that may be overkill. It worked fine just hooking the 10 amp charger on to one of the outside batteries and it charged the whole pack. I used the 20 amp setting for a while and it too, worked fine except that the + clip got really hot. It definitely needs a permanent cable for that much amperage.

JohnnieB, can you help me with this? I've got this inverter generator:

http://www.homedepot.com/p/Ryobi-2-2...2200/203617901

They say its 2200 watts, but only 1800 running watts. It runs the 30 amp cart charger just fine, and I added in the 20 amp 12 volt charger and it ran them both at the same time; it did seem to be straining. So how big of a 12 volt charger could I add to this system that would work at the same time with the cart charger? This is kinda important because I charge up the cart when I leave and just let it run until it runs out of gas. It only holds a gallon. I'd like to be able to hook them both up at the same time when I leave. One of the 3 bank chargers might still work well; just disconnect one or 2 when trying run it with the cart charger.

As always, thanks for any help.

[JohnnieB]

The 1800W is maximum continuous load, but it will supply up to 2200W for up to a minute or so. Devices with motors and/or transformers draw 2 to 4 times their nominal (running) power when they start, so you don't want them starting at the same time.

Plug in (turn on) the highest power using device first, let it stabilize, then plug in the next highest power user.

In essence, you will be charging two golf cart battery packs. Despite the difference in voltage, they both store the same amount of energy since they are both made up of six 6V-225AH batteries. Both chargers will be putting out their max amps when they first come on and their output amps will decrease as the on-charge voltage increases above about 2.25VPC (Volts per cell), which is about 13.5V for the 12V pack and about 40.5V for the 36V pack. Depending on the SoC the pack was discharged to, that may be anywhere from an hour or so up to 2 or 3 hours.

The trick is to find out how many watts each charger draws when it is putting out its max amps after the initial surge. If it is over 1800W, you'll have to use a charger that draws less power for one of the battery packs, or wait until the output amps start to decrease before connecting the second charger.

The labels on the chargers ought to state the running amps. The max the generator will put out continuously is about 15A AC, so the sum of the two needs to be equal or less than 15A.

Or you could use something like this: https://www.amazon.com/P3-P4400-Elec...ds=kill+a+watt and actually measure how many amps (or watts) they draw.

[coosa]

Thanks JohnnieB - I had already been running the cart charger for a while before plugging in the other charger; that might be the only reason I got by with it. I've been reading on some home solar sites today, and I haven't found much talk about what kind of backup charger to use with a solar system. From what little I've found, I think the 3 bank marine charger I was thinking of may be a bad idea because ultimately they are all hooked together anyway.

And for anyone wondering, I've read that I really need a vented cabinet with this much power inside the house. It shouldn't be hard to make one with 2" pvc pipe. Thanks for all the help on an OT question.