Marine battery switch for equalization

Re: Marine battery switch for equalization

706jim wrote: »

I'm thinking of connecting two strings of 4 L16's using a marine battery switch such as made by Guest.

These typically have settings for bank 1 bank 2 or both as well as off.

Would seem to be a simple solution to reduce the amount of current needed to periodically equalize these fairly large batteries with the limited amount of panels I have at the moment.

As my inverter is only 1500 watts at 24 volts, current should never exceed 80 amps or so. These switches are rated at about 400 amps continuous 600 amps momentary.

Thoughts?

I would be very careful about connecting two battery banks in parallel through the switch when the two banks might be at different states of charge. With the wide voltage range of lead acid batteries and the low internal resistance the current flow between the two banks could easily damage either the switch or the wiring. Not a good idea.
You could put in a mechanical stop to prevent putting the switch in the BOTH position, at least requiring a deliberate removal of the lockout is you know the strings are balanced well enough.

Re: Marine battery switch for equalization

706jim

And if I read gww's post correctly, it sounds like it will be ok if the inverter charger drops the current as the voltage rises to 28.0

My point is if you eq at 28 volts. Getting to the 28 volts takes alot and after you reach the 28 volts you need very little current. What I do when the eq last longer then the sun, or if I don't want it to take forever. I will drop loads use solar imput and the grid and inverter chargerer and put them together to get the battery recomended max charging amps to get the battery charged as fast as possible so that when I start the eq I will be using very little juice to keep them at that level for as long as I need. I understand vtmaps position that you can take care of parelel batteries better by eq independently cause during normal use they due to being in parelel may be off from each other during normal charging.

I am no expert. I am pretty lazy and figure everything is a compermize. I would not personally wan't to seperate my bank due to the extra oversite it would take,in my mind. Things like when I put them back together are they in the same state of charge so there is no great influx of current rushing from one bank to the other due to different states of charge. Which one need what?

I am not saying what you should do but what I would do. If I had your solar and your batteries, I would either reconize that I need more or I would reconize I am going to have to use grid/generator alot for charging. I would pay real attention to my cable lenths and try to get it perfect as possible and then watch the banks as I go and if I get imbalances, try to figure out why and or rotate the batteries every so often (not easy either).

The one benifit of being able to seperate you bank would be if you had a battery go bad you could just use half of you batteries while you addressed it.

When Chris olsen was doing parelel batteries he put cheap voltage meters on each so he could se imbalances as early as possible while the batteries were still in use.

Did you get the point that caraboohoot was making?

My oppinion is, If you seperate your banks and use them that way, you lose what your banks could provide too loads and have to remember which is charged. If you charge them seperatly and then combine them you have to make sure they are at the same charged stage before putting them together, which means you have to take both out of service to charge.

I may not know what I am talking about either.
gww

Re: Marine battery switch for equalization

vtmaps

All batteries in parallel will have the same voltage, but the current may be be different in each string. A voltmeter may be used to monitor battery banks, but you need a meter for each battery in the string. You might find, for example, that a string of four 6 volt batteries has a voltage of 24.0 volts, but three of the batteries are 6.1 volts and the other battery is 5.7 volts. That would be an indication that there is a problem in the string.

I don't believe he was doing every battery, I think he had mutiple parelel strings and he was putting a volt meter on each 12v/24v (whatever he had) string and then he was looking for a half volt differance in the strings and then he would address the issue ie check connections, rotate, chk batteries, ect.

As a practical matter, if you have parallel batteries, a reasonable monitoring protocol is to use a current clamp meter periodically to see that the current in each parallel string is the same. When you find different currents in each string... that's a good time to resolve that your next bank will not have parallel batteries.

This is very good advice also.
gww

Re: Marine battery switch for equalization

706jim wrote: »

My point is that when the voltages of the two 4 battery strings are similar

If the strings are connected, the voltages are identical. If they are not connected, under what conditions are you measuring the voltages? (that is, have both batteries been disconnected from all loads and charging sources overnight?)

706jim wrote: »

only a small amount of current required to drop the strings down to their normal "resting" voltage which is around 24.8 volts.

What type of L-16 batteries are these? The ones I'm familiar with have resting voltages significantly higher than that. I think it would be worthwhile to compare the voltages on each L-16 in each string.

btw, After charging a battery, its voltage will be higher than its resting voltage because of surface charge. It can take hours for this charge to bleed off in a resting battery, but it can bleed off pretty quick with even a modest load.

--vtMaps

Re: Marine battery switch for equalization

706jim wrote: »

Trojan L16's; the 370 Ah version. I have them sitting in my garage, new from the supplier and their voltages range from 6.17 to 6.20. Four in series would be pretty much be the 24.8 that I mentioned.

Hopefully your voltmeter needs calibration.... According to Trojan, your batteries should have a resting voltage of 6.37. That's 25.5 volts for a 4 battery string.

--vtMaps