Things I dont understand about batteries and wires

[ip485]

I realise there are a few important things I dont understand and have a feeling I should! (Well probably more than a few, but any way!)

- charging batteries, and in particular AGM batteries. There seems to be two schools of thought, dont charge to quickly and charge very quickly! They cant both be right. One school seems to reckon with AGM you can dump lots of charge in quickly because they are good at initially absorbing charge. Of course, I like that answer because the quicker you can replace the charge, the better. Which brings me on to the second question - so if you have two chargers, say one 100 amp and one 50 amp can you run them at the same time, and will they each "know" when to reduce the charge as the batteries approach a full charge.

- and on a different subject, some electronics (for example with switches on the main panel) have a power supply of two wires from the panel providing +ve and -ve both routing back to the main panel, whereas other equipment will have a positive supply with the earth routed back to the main earth on the engine perhaps, or that is my impression. What are the reasons and rational for each approach?

 

[RichardS]

Some switches and panels have switch lights and/or panel lights which might explain the extra connections?

I don't think that AGMs need a very different charging regime to other maintenance free batteries. All lead-acid batteries suffer from being charged too quickly but a very large current would be required to make a significant difference.

Richard

 

[Lon nan Gruagach]

so if you have two chargers, say one 100 amp and one 50 amp can you run them at the same time, and will they each "know" when to reduce the charge as the batteries approach a full charge.

You could.... with some fancy electronics to switch one charger on and the other off but that would just be (an expensive) way to build a smart charger and probably not as good as an off the shelf one. Fancy ones have 3 stages: rapid charge, float charge and maintenance. Even fancier still have temperature sensing to know just how hard it can push.

- and on a different subject, some electronics (for example with switches on the main panel) have a power supply of two wires from the panel providing +ve and -ve both routing back to the main panel, whereas other equipment will have a positive supply with the earth routed back to the main earth on the engine perhaps, or that is my impression. What are the reasons and rational for each approach?

So long as the -ve gets back to -ve some how, electrically its not that important. But (there always a but) its bad practice to mix and match. My preference would be all wires come from (and return to) the switch panel where there is a -ve distribution system. Sounds like at least 2 generations of wiring on your boat.

 

[GHA]

Not as much to be gained by upping the charge current as you might think -
http://www.pbase.com/mainecruising/effect_of_charge_rate_on_agm_battery

 

[lpdsn]

- and on a different subject, some electronics (for example with switches on the main panel) have a power supply of two wires from the panel providing +ve and -ve both routing back to the main panel, whereas other equipment will have a positive supply with the earth routed back to the main earth on the engine perhaps, or that is my impression. What are the reasons and rational for each approach?

Think of it mentally like a three wire system. +ve, -ve & Gnd, even though you know -ve and Gnd are almost the same thing and if you mix them up things will still work.

 

[RobbieW]

Not as much to be gained by upping the charge current as you might think -
http://www.pbase.com/mainecruising/effect_of_charge_rate_on_agm_battery

True for returning to 100% but for getting to 80-85% then letting solar take over there was a demonstrable difference, see page 3 of the link

 

[prv]

Think of it mentally like a three wire system. +ve, -ve & Gnd, even though you know -ve and Gnd are almost the same thing and if you mix them up things will still work.

What on earth does wiring some devices to the engine negative and others to the panel negative have to do with three wires or grounding?

It's an odd practice, though not intrinsically harmful assuming the engine and service negatives are tied together as they generally are. I wonder if the person who did it was more used to cars?

How have they connected all these negatives to the engine? Unlike a panel there isn't generally a busbar there to attach them to, so it seems like this could easily end up with a mess of far too many terminals on one bolt.

Pete

 

[lpdsn]

What on earth does wiring some devices to the engine negative and others to the panel negative have to do with three wires or grounding?

Que?

After disagreeing with me you've then gone on to agree with me that it's better not to use the ground on the engine as the -ve busbar. How many separate set of wires do you count it as? Four?