Charging deep cycle batteries on the hook

[john61ct]

Originally Posted by kamikater

i don't mind a couple extra bucks

In that case go for 75/15 per each panel

> can you tell me why a Victron SmartSolar MPPT 75/15 is better than a 75/30 or 75/20?

The second number is the maximum amps **charging output** the SC can extract no matter how big / many panels.

A 125W panel will very very rarely actually produce that much.

Say your charge setpoint is 14.6V (depends on the battery of course).

Multiply that by the 15/20/30A to get the SC max potential **watts** output.

If the panel is rated say only 10-20% above that number, you save money, maximum output per SC dollar.

If you think getting that extra 2-5% is worth paying almost double, go for it.

But getting a 30A SC for a panel that will never put out 9A is throwing money away.

Victron's tremendous value pricing on the lower-amp SCs is what makes one SC per panel economically possible.

Having more SCs does take space, bit more wiring, etc, but dramatically optimizes for shading conditions and gives redundancy.

[kamikater]

thanks to all of you,
great forum,great help,nice people!

young cruising couple here,figuring stuff out since 2017.

greetings from costa rica!

sv/lucy
westsail28

[noelex 77]

Originally Posted by john61ct

Only mentioned for keeping things inexpensive.

When you are living permanently from the power generated by 250w of solar, in my view, recommending the purchase of a controller that will compromise the output of the panels is bad advice.

The difference in price between the Victron Smartsolar 75/15 and the 100/20 model is only about £30 ($38).

[smac999]

You are going to have a hard time charging a battery bank to full with 250w of solar. Unless the boat is shut off. Or you run the engine every morning.

Do you have a fridge?

[wnischt]

If you are charging AGM batteries, from what I have read, you want to limit the voltage to 14.2V. I ruined $800 worth of batteries by using a higher charging voltage.

[Mike Banks]

Yes. You can use the unregulated input to equalise the cells in a fully charged battery but--no longer than a 12 hour day--no more than about 24 volts--and at a low current--so maybe only ONE panel.

Do this every so often, about once a month.

[john61ct]

Each decent battery has its own profile, detailed in its spec sheets / manual.

Every decent maker has tech staff you can contact to discuss questions you may have.

[Cadence]

Being totally ignorant on the subject there is a purpose for that controller. I would guess you may be harming your battery life?

[thomm225]

Since your current setup can charge up the batteries totally by noon you have time to experiment as I am doing.

I have a few PWM controllers and a Victron 75/15.

I deploy my panels as needed with some going thru the PWM and others the Victron MPPT and if I need to some panels are hooked directly to the batteries

[roland stockham]

It depends on what batteries you have. If they are flooded cels you need to upgrade your solar contrallor to one that allows you to set a voltage of 14.8v min. That does not need to be an expensive on but either one that allows you to sellect for batt type of designed for FLA's. 14.2 will charge sealed cells (but with extended charge times) but does not fully charge FLA's and you will get problems with sulfation. Fully charging sealed cells is always a problem if you live on the hook because they are limited to 14.4v (gassing voltage) so need very long charge times once bulk charge has finished. Bulk charge gets to around 80-85% but because of the lov voltage you will be down to quite low currents at that piont, increasing to 14.8 will more than double the charge rate so substantially shorten the time to get from bulk to float levels. I like to get batteries to float state at least once per week which pretty much elliminates sulfation. This is the main reason sealed cells on sailboats have less than half the life of FLA's. They are no problem on power boats and cars or boats that plug in at a dock on a weekly basis because of the long engine run times or periods on mains power charger. On the hook I tend to go for a program where you fun the engine once a week for 2-3hrs in the morning so that you are up to about 90% SoC (assuming smart regulation on the alternator) buy the time the solar kicks in and then have a full day on solar charge to ensure you get to 100%. This assumes you solar system will keep up with you daytime load plus enough to give about C10 charge rate and will therfore give about 5hrs at the batteries acceptance rate. The only reliable way I know to check you are at 100% is to measure the charge current, it should be dawn to min 5%, ideally 2%, of the banks Ahr capacity. 5% is fine for the weekly charge but getting to 2% once a month definatly improves battery life. provided you can monitor the current into the batt bank rather than the solar output you don't need to switch of everything to do this just monitor the bank input to ensure continuouse charging and that voltage remains at 14.8v. I have never done this on a sealed bank so not sure what the % would be to indicate full charge but have my doubts you can ever get to it without shore power, it just takes to long! Following the regime you don't need an equalization charge which is generally not advised for sealed cells because it causes water loss. Some high quality sealed cells do have recombenent tech to reduce water loss but it puts the intial cost very high and personally I don't think it is worth it.

[roland stockham]

Originally Posted by ablefollower

No, don't touch anything. Those are all perfectly good numbers, considering your outdated battery technology.

If you really did need an upgrade (sounds like you do), then start work on designing and saving up for your LFP replacement system, while will be far superior.

http://www.cruisersforum.com/forums/...up-226542.html

See this and other threads for design tips.

L/A batteries are not outdated tech but the poster did not acually state what batteries he had so we don't know. Broadly there are three techs available, FLA, sealed LA and Lithium. They can ALL be the most appropriate tech in different boats depending on size of boat and electrical load which we also don't know. Given all the parameters needed you can make an assement on what is the most cost effective solution for a given boat and usage pattern but the idea that lithium is 'up to date' and anything else is 'out of date' is nonsense.

[roland stockham]

PS, in answer to the origional question. Yes it is fine to insert a switch that connects solar directly to the batteries if they are FLA's but you have to monitor it carfully and disconnect before getting to 15v otherwise you will exceed the max volage on mosr of your electronics. Watch carfully because once batteries are fully charge the voltage can rise qite quickly. With sealed batteries you have to stop at 14.4v so probably would not achieve much. If you are using sealed batteries you system is probably as good as it can be but don' expect long life from them as they are good for marina boats but not ideal for most cruisers because of short life span and very long charging times to get above 90% SoC.

[Adelie]

Originally Posted by smac999

You are going to have a hard time charging a battery bank to full with 250w of solar. Unless the boat is shut off. Or you run the engine every morning.



Do you have a fridge?

That depends on their typical overnight usage.
250w thru an MPPT controller should average 75amp-hr per day production with panels mounted flat.

[john61ct]

in excellent insolation days

latitude, temperatures and overcast being major variables