Don't know what this is?

tednbren

Trying to simply as much as possible for a simple answer. I have eight 6 volt batteries in series and parallel. (12 volt system) I have five 200 watt panels hooked in parallel to a Coleman Air 160 amp controller. When I take a battery reading anywhere on the batteries I get for example 12.79. The reading is the same everywhere I check. So far so good. As it should be. Now how to explain the question. When I take a reading across the batteries one get one strange high reading. Like criss-cross
pos-neg one way is the 12.79. (Basically, I read positive on first set and negative on fourth set.) When I go the other way opposite corners, criss cross, I get this strange reading of say 15.2. None of the other readings are off. I know I haven't explained it well, but does anyone know what I mean. Has anyone an explanation? These terminals (the high reading) have no other wires on them, just the one connecting in series and parallel. Any ideas?

Cariboocoot

Re: Don't know what this is?

Each string reads 12.79 Volts, yes? And when you take a diagonal reading you get the higher Voltage? There should be no higher Voltage than the highest individual string. It sounds as though you have high resistance in the inter-battery connections; when you check diagonally the 'extra' Voltage is picked up from the parallel paths (it would not be present on a single string because the connections between strings add more resistance than the parallel paths take away). This is why having three strings in parallel as you do is not recommended.
Check for Voltage potential between the three positive posts; it should be zero. Do the same for the negative posts.
Wiring resistance makes trouble for current sharing. Look at method #3 here: http://www.smartgauge.co.uk/batt_con.html

Or I could be completely misinterpreting what you said.