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canuck sailor · May 2011

Re: Help!

That's how I thought it worked. btw, that's the best explanation I've heard yet, about lots of electrons hurrying over - nice little picture that I can understand.

canuck sailor · May 2011

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BB. wrote: »

To cut down on charging current, put an on/off switch in the lead to the battery and turn it on to charge, and off to stop charging... that is pretty much what a PWM charge controller is doing--just a bit faster On/Off switching.l

I've been doing pretty much that by taking out the fuse in the line to the battery, while waiting for the new PMMT to be delivered. Looks like I'll be doing more of it while I look for another controller, one that works.

tabbycat · October 2011

Re: Help!

Instead of one 450 AH 12 volt battery bank why not two banks at 225AH 12 volts charging them separately. This will double the current from the panel relative to the battery capacity. thanks. Steve S.

tabbycat · October 2011

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Carrying this argument to a possibly illogical conclusion, an MPPT controller could charge each battery separately with the voltage differential of 17 volts for the panel and 6 volts for the battery providing quite a current boost. You would have to switch the MPPT controller from one battery to the next manually unless you can find a way of doing it electronically. The assumption is that there is plenty of time for charging to occur which is usually true for boats which are idle most of the time. Thanks. Steve S.

niel · October 2011

Re: Help!

manually switching a battery bank from one to another isn't so hard.
http://www.solar-electric.com/basw1300amp.html

tabbycat · October 2011

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Is there such a thing as an MPPT controller that could be used with a six volt battery bank? I don't see any ads. The manufacturers talk about twelve thru forty-eight volt banks. Thanks. Steve S.

BB. · October 2011

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I have not seen a 6 volt MPPT charge controller. Operating at such low voltage batteries would make for an expensive installation (large currents, very low voltage drop allowed for proper operation).

Note, you can possible put multiple charge controllers across 12 volt batteries in a 24 or 48 volt--But the issue of different grounds, multiple arrays, multiple controllers, etc. make it difficult to put a safe and sane system together.

Do you want to start a thread about your own system and start from the beginning about what your specific needs are?

-Bill

tabbycat · October 2011

Re: Help!

I'm trying to come up with a solution for the original problem in this thread. The writer had a large battery bank (four) of six volt Trojans and limited space for solar panels. Trying to charge all the batteries at once with his 123 watt panel would barely tickle them. If he could charge only one or two of the batteries at a time his panel would be more effective. Using an MPPT controller with his 17 volt panel and only one six volt Trojan would provide a bulk charge to the battery. The limitation is that he can only charge one battery bank at a time. The lack of deck space is common to many boaters. Using an MPPT controller to increase the charging current rather than adding more panels may solve his problem. If there is no low voltage MPPT available he could go to a higher voltage panel and use a standard MPPT. The voltage difference between a 12 volt battery bank and a 24 volt panel would provide significantly more current. Thanks. Steve S.

mike95490 · October 2011

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If you only have 500 watt hours of harvest, it makes no difference to charge the entire bank, or only part of it. The batteries will all suffer equally. Or you can dispose of enough batteries to enable charging the remaining one. But you can't get more then you harvest. Fewer batteries has the advantage of less "self-discharge" loss, and AGM batteries have less loss then flooded. But switching between 2 dead banks won't help.

Cariboocoot · October 2011

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An MPPT controller provides a small advantage over a PWM type under most circumstances. About 10% more available current. This becomes more significant with the increase in array size. The cost of such a controller is so much greater than a PWM that it is not economical to use one on a small system; better to spend the money on more panel.

A battery bank should be charged as it is used: if all batteries are used at once to power the inverter, they should all be charged at the same time. If you charge them separately (as in putting two 12 Volt arrays & controllers on a 24 Volt system) they will not perform consistently across all batteries. To say nothing of the difficulty of isolating grounds (since the negative of one of the controllers needs to connect to the positive of the other at the battery bank).

There are no 6 Volt charge solar controllers because there are no 6 Volt panels and no 6 Volt inverters. Oh there might be some odd ball equipment out there somewhere, but basically it isn't done.

BB. · October 2011

Re: Help!

It is tough... I am not sure I would bother with switching banks... One more thing on the "to do" list and something that can be forgotten.

I would just put the number of panels and an appropriate solar charge controller on the system. And you will have to use the boat's electrical system to make up for any charging in excess of what the sun can provide.

If your solar panel Vmp is significantly higher than 17.5-18 volts or so--You will probably want to install a MPPT charge controller. For example a Vmp=24 volt panel on a PWM controller charging a 12 volt battery bank will be around:

17.5 v / 24 v = 0.73 efficient relative to Vmp=17.5 volts

So, that is a fair amount of energy to "throw away" by using a PWM controller over a MPPT.

If your boat is "unattended/unconnected to shore power" for months at a time--perhaps that is too much battery for too little panel.

If you run the boat once a month anyway (or have shore power for a day) and the panels otherwise keep up with your loads (mooring light, etc.), then I would not be too concerned.

If your loads are >> than the solar panel output--then there is really nothing you can do than figure out the most cost effective method of keeping your battery bank charged (running main motor, running a small genset/battery charge, getting shore power, etc.).

And with flooded cell batteries--you should be checking water levels at least every month or two (especially if they are cycling and not just sitting at a low float voltage)--So somebody will have to be there anyway.

-Bill

tabbycat · October 2011

Re: Help!

The less you try to accomplish the more likely you will succeed. It might pay to start from the beginning with an energy audit to see if he really needs such a big battery bank. There is a difference between needs and wants. Once his needs are determined then he will have to design a system that will satisfy his requirements. He may have to go on an energy diet and cut his consumption down to what his charging system can provide. Thanks. Steve S.

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