Battery Backup Wiring Question

[Dom]

So for the last 4 years, I have been using 3 Deep Cycle Marine Batteries as a battery backup to my tank.

The batteries are 12 volts and rated 85 amp hours, giving me a total of 255 amp hours.

The batteries are connected in parallel, each with it's own 1.25 amp charger. In turn, they are wired into a Cobra CPI 2575 inverter, which is rated at 2500 Watts continuous and 5000 Watts peak.

Of course, this setup is connected to a 15 amp 110v AC auto transfer switch.

All of this is is on and ready to provide power if the utility company goes off line.

Recently, I noticed that my battery voltage readout on the inverter is 12.9 volts instead of the usual 13.1 volts. I attributed this to battery age and made an inquiry to a friend about replacement battery recommendations.

This turned into an evaluation of my setup, which was labeled "inadequate" as I do not have battery isolators in the configuration and lack a startup capacitor.

A startup capacitor would correct the problem I have where the protein skimmer sometimes won't start when switching to battery power.

But while extremely knowledgeable on the subject of circuits, this person is a quite a bit of an alarmist, telling me that I'm lucky I haven't set my house on fire.

I would think that after 4 years of this configuration, if there was a problem, it would have shown its face by now.

I was also told that my setup was "grossly inefficient" and that I was cooking my inverter by leaving it on all the time.

Please... don't tell me what I want to hear. Tell me what you think.

 

[Mjrenz]

I think I want to see some pictures of your setup . Batteries do go bad overtime so you could either take them into an auto parts store to be tested or purchase a battery load tester to check then yourself. It sounds like your friend may be a litte cynical so I wouldn't panic just yet

 

[Dom]

I think I want to see some pictures of your setup . Batteries do go bad overtime so you could either take them into an auto parts store to be tested or purchase a battery load tester to check then yourself. It sounds like your friend may be a litte cynical so I wouldn't panic just yet

Pictures... of course. I'll post them in a while.

 

[Dom]

This is my 110 volt auto transfer switch. It allows current from the utility company to bypass the battery backup system when the utility company is up and switches over when the utility company goes down.

This is my charger. It is rated at 1.25 Amps. I have one of these on EACH battery.

This is the deep cycle marine battery I use (I have 3). It is rated at 85 amp hours.

And this is the inverter that I have installed. It is rated at 2500 watts continuous and 5000 watts peak.

This is the setup.

I can see why battery isolators would be important. Without them, you can never true voltage readings of the individual batteries without disconnecting them. It will always be voltage readings of the battery BANK as a whole. Hope this additional information helps.

 

[KStatefan]

I would be concerned about gas coming from those batteries but do not know if that is a valid concern.

With the batteries hooked up in parallel you would only need one charger.

 

[Mjrenz]

I agree with one charger, I would recommend putting the batteries in boxes, I had a deep cycle battery explode once and I'm glad it was in a box. The issue you are having with your skimmer starting is likely due to the size of the cable you are using connecting the batteries to the inverter. 2500 watts at 12 volts is a little over 200amps. I would suggest using 4/0 welding cable to connect the batteries together and to the inverter

 

[Mjrenz]

A also, I don't think isolators are necessary, you could just disconnect the batteries once a year to check them individually

 

[Mjrenz]

I would be concerned about gas coming from those batteries but do not know if that is a valid concern.

With the batteries hooked up in parallel you would only need one charger.

They will emit some hydrogen gas but personally I wouldn't be concerned unless they are in a small unvented closet

 

[link81]

I agree totally with @Mjrenz you're power supply leads to the inverter are totally inadequate. those need to be much larger.
I think you'll also need to change it to one charger for the bank. currently you basically have 1 big battery being charged by 3 separate chargers. I'm not sure if a 1.25 amp charger will be big enough for the 3 batteries. might need to upsize it a bit.

 

[Mjrenz]

I agree totally with @Mjrenz you're power supply leads to the inverter are totally inadequate. those need to be much larger.
I think you'll also need to change it to one charger for the bank. currently you basically have 1 big battery being charged by 3 separate chargers. I'm not sure if a 1.25 amp charger will be big enough for the 3 batteries. might need to upsize it a bit.

I was actually just thinking about that, the size of the charger needed would have a lot to do with the standby current draw from the inverter while it's on without a load

 

[Dom]

I agree totally with @Mjrenz you're power supply leads to the inverter are totally inadequate. those need to be much larger.
I think you'll also need to change it to one charger for the bank. currently you basically have 1 big battery being charged by 3 separate chargers. I'm not sure if a 1.25 amp charger will be big enough for the 3 batteries. might need to upsize it a bit.

I do have thick cables... I think they are 4 gauge. I plan on using them when I rebuild the backup. So yes, I agree that the current cables are inadequate.

It was suggested that I goto a 10 amp charger as 1.25 amp chargers... even 3 of them... doesn't recharge the system fast enough.

I'm planning a complete rebuild and am looking for suggestions. I may even start a build thread on the new backup.

 

[Dom]

.

 

[link81]

i wonder if an apex could be set up to power on the inverter when it detects a power loss.......
I bet with a little modding of the inverter to add a relay contact into the inverter power switch it would be fine.

 

[link81]

I do have thick cables... I think they are 4 gauge. I plan on using them when I rebuild the backup. So yes, I agree that the current cables are inadequate.

It was suggested that I goto a 10 amp charger as 1.25 amp chargers... even 3 of them... doesn't recharge the system fast enough.

I'm planning a complete rebuild and am looking for suggestions. I may even start a build thread on the new backup.

even 4 gauge is on the small side for that inverter, but i doubt that your tank consumes anywhere near 2500W.
my 40B only uses about 3.5 amps when both heaters are running. (420W) so i'm fairly confident thet 4G will work fine.
as far as a charger, you're definitely going to want a smart one, that will charge at say, 10A until near full, then drop down into a trickle charge mode to maintain capacity.

 

[Dr. Dendrostein]

If my setup, I'd have all pumps, and accessories run on 12v dc. This would happen in the planning stages, have a converter, powered by 120v to power 12v dc. As it's setup now, the inverter draws alot amps, less battery use . But just my thoughts.

 

[BZOFIQ]

Ok, so a lot of different thought are going through the head.

Supply wires: You need heavier gauge by far, probably as thick as the terminals will accept.

Since there are 2 terminals for both positive and negative, I would probably scale back to 2 batteries each feeding the inverter directly. An inline fuse (properly rated) and a disconnect between each battery and the inverter is in order as well.

 

[BZOFIQ]

As to the skimmer not starting up, does your inverter produce pure-sine wave 120V out?

From my experience some pumps and powerheads will not run on anything but pure-sine wave; this is why I bought pure sine inverter generator and only keep pure-sine battery backups.

 

[BZOFIQ]

I do have thick cables... I think they are 4 gauge. I plan on using them when I rebuild the backup. So yes, I agree that the current cables are inadequate.

It was suggested that I goto a 10 amp charger as 1.25 amp chargers... even 3 of them... doesn't recharge the system fast enough.

I'm planning a complete rebuild and am looking for suggestions. I may even start a build thread on the new backup.

Definitely a larger charger!

It will take forever for that bank of batteries to provide meaningful backup source in the event of total drain.

You need to accommodate natural battery discharge/loss in addition to what the inverter draws on standby. I'd say at least 15+ amps. (even 15A across 3 batteries might be too slow a charge and will slowly damage all batteries) The trickle chargers you've employed until now are only good for keeping your battery at full, they are not designed for charging, will !destroy! your battery.

With 15 Amp charger and 2 batteries you'll be looking at total recovery time of about 12-16 hours.

 

[BZOFIQ]

i wonder if an apex could be set up to power on the inverter when it detects a power loss.......
I bet with a little modding of the inverter to add a relay contact into the inverter power switch it would be fine.

It can with proper relays, but it too would have to be powered by and auxiliary power supply plugged into a small battery backup, or it will go dark with power loss.

 

[link81]

It can with proper relays, but it too would have to be powered by and auxiliary power supply plugged into a small battery backup, or it will go dark with the power loss.

that's easily solvable with a small pc UPS. although with all the expense and effort going into this, I wonder if an upsized ups wouldn't do the same thing easier and cheaper. albit at the expense of some runtime. If long term power outages are this frequent, think about a small backup generator and a midsized UPS for the fish tank. Can get a self contained 1500va UPS for about 150. then a small generator for 300 or so, and have powerless runtime measurable in days, not hours.