batt switch

[ron45]

It is possible I'll need to switch between two separate banks in the same room. These would be two banks of eight 6v. L16 and twelve 6v. Surrette S530s.   I now use a Perko marine switch as a disconnect on the Surrette bank. This is an enclosed make before break. These are relatively inexpensive. I believe the way it is configured it could be used an A or B switch but I could be wrong about that. Could I get a way using one of these?  This would then be a manual operation. What say you?  Been off grid since 83 with few of the things code people like to have you buy.

Ron

[offgridnut]

Those marine Switches are great.  I have one on a dual battery grid tie so that they can have the large set for backup and use the small set to keep the sell volt losses minimized.  The Electrical inspector didn't have a problem with it as it was rated to handle the Volts and Amps. As the Switch is moved in the right direction, both batteries are online together momentarily so that the power flow is uninterrupted. Very Nice.

[ron45]

You are saying just what I wanted to hear. So now I'm a little worried. I am not a big fan of being overly cautious.  I've been warned twice since writing my question here, that with a make before break switch there is a short period of time where current and voltage from both banks is present. [ the whole point of the switch] They suggested not using that type of switch plus shutting down all incoming power sources to avoid damaging the inverter. This seems like excessive fear and loathing to me. The banks and controllers should act as buffers for any incoming voltages or current shouldn't they?.  I liked the make before break mode because of the absence of arcing. But I guess if the switch is sealed it shouldn't matter. I've been talking to people yesterday and today who have to cover their butts and are imagining the worst I guess.

How long have you been using your switch in this manner? Is it a Perko? I ask because these are very reasonably priced. under $40. It does not sound like you disconnect anything before using the switch. Is it possible your grid tie situation is more suited to using this type of switch?

I just want to be sure about my application situation. One of the people who didn't like this idea was an electronics engineer with a military background. He worked at China Lake for most of his  career. So he is ultra cautious. It is an ordinance R&D place for the Navy. Do you know the amp/voltage rating of your switch? The voltages I'm dealing with are two series strings of 109.5 volts at  14.9 amps max. These Perkos can see 360 amps intermitent up to 48 volts. The amp potential in my two banks is very high. But I'm not enough of a tech guy to know if that matters. It does if you drop a pair of pliers in the wrong place. {;^)>

Ron

[offgridnut]

The Perko switch should not be used on the input side of the PV.  It should be installed between the batteries and the positive bus where the voltages are no higher than 48V nominal.
The switch that I installed has been service for about 6 months and switched back an forth numerous times under varied circumstances.  There is no indication of arching. 

[ron45]

That's a good point, thanks. The people on another forum are worried about spikes between the banks. I'll talk to Rolls/Surrette tomorrow. Here's some of what I'm getting at the other forum.


Quote from: Ronnn on Today at 11:39:18 AM
Can changing the mode of operation of the switch i.e. not a make before break, make a difference in the switching procedure.

I'd be very reluctant to do that - you can (almost certainly will) get some very nasty spikes while changing.


Quote
These would be two 24 volt banks. One possible at 24.8 the other at something over 25 volts.

If you have one bank at 24.8, and one at 25.3 (half a volt difference), and assuming for a moment these are quite large cells of very low internal resistance (lets allow 0.2 milliohms per cell, which is typical for 500 amphour AGM) - that's 2.4 milliohms, plus cables and jumpers - lets call it 4.8 milliohms total, would see a peak current of 100 amps flowing between the cells briefly, while both are switched in.

That current will be less if your batteries internal resistance is higher, and/or the cables are not basically welding cable

Also, the current flow will VERY QUICKLY drop to a few amps as the two banks equalise.

In reality - if your battery banks are not vastly different (like one nearly flat and one on float) - I don't think you'll have any problems with the A/A+B/B switching. End Quote


If I'm understanding this post correctly he's saying `you better not,'  then `ya but ok do it' in the last line.

Lastly I have a Perko as a shut off between the array and the + buss for all the panels. Been there a few years but I probably haven't used it twice. Total amps less than 30 max volts 48.

Ron

[mike90045]

if both banks are charged, why are you switching?   The worst case is when you are running, and the bank gets low and you want to switch to get some more juice from the other.  That is when you will see way more than 100A.  The arc could even weld the switch solid, in mid rotation, it's not designed for a huge battery bank, generally just a couple of group 27's in a bilge.  and the glitch, will likely make your inverter drop out and reset, but I don't think it will blow anything up.