MPPT vs PWM cotrollers?

[noelex 77]

Originally Posted by john61ct

If so the Hold Absorb Time settings should be increased not shortened.

Fortunately absorption time is not a often a critical parameter. It is still helpful for battery life to set this parameter roughly correctly.

The default absorption time varies considerably between manufacturers. Anything from 1hr to 3hrs is used. So there is little consensus on the ideal absorption time. The Victron controllers use an adjustable absorption time based on time taken to reach the bulk voltage, which is a more intelligent system, but is not foolproof.

It is sometimes suggested in forums that default absorption times are too short. This has not been my experience, with overly long absorption times being more common in my experience.

It is worthwhile to measure the return amps just before the absorption timer runs out. If this is done over a few typical cycles it will settle if the absorption time is appropriate in your system.

With wet cells a slightly longer absorption time is better than too short, but the opposite is true of gel cells.

The only real danger with multiple controllers is that the absorption time countdown timer is sometimes not started on one or more controllers even when the absorption voltage has been effectively reached. For this reason there is more risk of an excessively long absorption time.

[john61ct]

There cannot be any one correct setting, it varies based on many interdependent factors, not just every boat's usage patterns but these change over time.

Yes, benchmarking against trailing amps is how you get the eggtimer approximately right, but heavier or lighter concurrent loads change things.

Best of course is a shunt at the bank initiating transition to Float based directly off endAmps marking 100% Full.

Maybe a half dozen vendors integrate the SC and BM to achieve that.

[contrail]

Originally Posted by GTom

An RF specialist might chime in, but I suspect the cables towards the panels would leak out the noise. Have to budget in shielded coax cables too for a cheap MPPT controller, to continue operating that 3k$ worth SSB set

Using a very early MPPT controller, about 17 years ago, I simply installed a bypass that went around it. When I turned on the SSB, I used the bypass and the panels charged the batteries, un-regulated. The bank was about 300 watts, to a 400 AH bank, and I just kept an eye on the voltage. Since the SSB can use a lot of current (I was a net controller), the voltage never got that high. When I was done, I switched back to the MPPT, which was quite noisy. I used a simple 1-2 battery switch to select the MPPT or the bypass, in order to handle any large current.

[noelex 77]

Originally Posted by john61ct

Best of course is a shunt at the bank initiating transition to Float based directly off endAmps marking 100% Full.

Agreed. Our last controller had this feature and it is the best way to set the absorption time. However, It is not difficult to measure end amps yourself. Most battery monitors will display the net current entering or leaving the battery. So it is easy to check if the absorption time is appropriate.

If you measure a few typical cycles you will know if your absorption time on average is correct.

Originally Posted by john61ct

Yes, benchmarking against trailing amps is how you get the eggtimer approximately right, but heavier or lighter concurrent loads change things.

The important parameter is the current entering or leaving the battery rather than the load.

[thomm225]

I still like the PWM Controllers for your average cruising boat going the minimalist route.

MPPT Controllers are way too expensive if there's no reason to have them

You can get a couple 12 volt batteries, controller, and 100 watts worth of panels for around $350.00 or so.

This should be about enough to run your lights, fans, autopilot, electronics, and inverter to charge your phone and laptop (and internet jetpack) for as long as you need it......

I've made do with a 60 watt panel for a week or so on vacation cruises. I have two additional 20 watt panels one of which I just hooked up so in the future I'll be in very good shape power wise .....

[john61ct]

Originally Posted by noelex 77

The important parameter is the current entering or leaving the battery rather than the load.

Yes I meant the changes in concurrent consumption require adjusting the eggtimer if direct endAmps regulation is not available.

If usage patterns vary widely from one day to the next then the eggtimer approach will be correct less often than a stopped clock 8-)

[john61ct]

Originally Posted by thomm225

I still like the PWM Controllers for your average cruising boat going the minimalist route.

MPPT Controllers are way too expensive if there's no reason to have them

You can get a couple 12 volt batteries, controller, and 100 watts worth of panels for around $350.00 or so.

This should be about enough to run your lights, fans, autopilot, electronics, and inverter to charge your phone and laptop (and internet jetpack) for as long as you need it......

I've made do with a 60 watt panel for a week or so on vacation cruises. I have two additional 20 watt panels one of which I just hooked up so in the future I'll be in very good shape power wise .....

This is supposed to be a cruiser's forum.

Most have much higher power requirements, and are away from mains for long periods in suboptimal conditions.

$350 is commonly the cost for one cell in the battery bank, or just the panels' mounting bracket.

[noelex 77]

Originally Posted by john61ct

If usage patterns vary widely from one day to the next then the eggtimer approach will be correct less often than a stopped clock 8-)

Many people do not realise the absorption timer only counts down when the absorption voltage is maintained. If the load is too high, the countdown is paused.

So while absorption time is not foolproof, combined with a sensible battery return voltage it is not as influenced by load as may be imagined.

So it is worth making some effort to set the absorption timer correctly especially with gel cells.

[john61ct]

Yes I hadn't come across that, my load vs capacity ratios and bank chemistries are such that voltage doesn't drop much in normal use.

[thomm225]

Originally Posted by john61ct

This is supposed to be a cruiser's forum.

Most have much higher power requirements, and are away from mains for long periods in suboptimal conditions.

$350 is commonly the cost for one cell in the battery bank, or just the panels' mounting bracket.

Actually it's the Cruising and Sailing Forum.

Also most here aren't actually cruising and have way more power than is necessary so spending too much for a cruise you might take one day can be quite a waste of money

$300-$350 dollars worth of batteries, panels, and controllers work fine for most folks that are not cruising long distance.

Also, some of us when we do sail/cruise for a few days to a week or two just want the basics when we go off the grid for a while since we have all other modern conveniences at our apartments and homes

Sometimes at the end of my vacation "cruises" the ice box is only just cooler than the water temp I'm sailing through but it's still cooler (that is unless I can get some ice at a store or marina I happen to anchor near)

Right now I'm charging two deep cycle 12 volt batteries with two solar panels totaling 80 watts through an $18.00 PWM controller. Total cost was right at $300.00. I also have a couple spare controllers ($12.00 ea), and one more 20 watt panel which I don't use at this time

This powers all my electronics, autopilot, plus my inverters (one 400 watt and one 1500 watt which is a spare) for my fan, fluorescent light, lap top, internet receiver, and to charge my phone.

[GTom]

Originally Posted by thomm225

I've made do with a 60 watt panel for a week or so on vacation cruises. I have two additional 20 watt panels one of which I just hooked up so in the future I'll be in very good shape power wise .....

Fridge, autopilot, Radar, pressurized water <-> engine use/shore power? I know, one can sail completely without electricity too... I suspect the typical cruising power budget will need more than a 100W peak...

Otherwise agreed, PWM is ideal for small, low voltage panels, mppt can't do much with 12V panels.

Originally Posted by thomm225

Right now I'm charging two deep cycle 12 volt batteries with two solar panels totaling 80 watts through an $18.00 PWM controller. Total cost was right at $300.00. I also have a couple spare controllers ($12.00 ea), and one more 20 watt panel which I don't use at this time

How much amperage do you see from the panels? How big are the batteries?

...

and to charge my phone.

My phone alone needs ~15+Wh (3.6Ah Li-battery), I think under realistic conditions (cloud cover, nonideal angle) it would alone require that 80W worth of panels...

[thomm225]

Originally Posted by GTom

Fridge, autopilot, Radar, pressurized water <-> engine use/shore power? I know, one can sail completely without electricity too... I suspect the typical cruising power budget will need more than a 100W peak...

Otherwise agreed, PWM is ideal for small, low voltage panels, mppt can't do much with 12V panels.



How much amperage do you see from the panels? How big are the batteries?

...
My phone alone needs ~15+Wh (3.6Ah Li-battery), I think under realistic conditions (cloud cover, nonideal angle) it would alone require that 80W worth of panels...

My two 12 volt batteries are in parallel. The batteries are AutoCraft Deep Cycle 24M that I bought for $88.00 each.

I don't usually ever hookup to shore power.

For the 5 years before that I had one starter battery (from when the boat had a diesel) and one deep cycle battery in parallel. It was a bit of a mismatch but worked for 5 years

The outboard I have now is pull start and has no alternator.

Under optimal conditions, the panels should provide a bit over 6 amps

Charging my phone and laptop from my 400 watt inverter takes very little from the batteries.

You have to realize that when I'm at anchor or even sailing there is very little load on the batteries. Just the autopilot, VHF, Depth, and maybe GPS when sailing usually ...... if the batteries happen to be low I go with just the autopilot for a few hours

At anchor, the main load is a fan that I run all night at times and sometimes my depth finder if I'm at a new anchorage and don't trust it.....

Anchor light is LED Lantern powered by AA Batteries.

[mikedefieslife]

Originally Posted by thomm225

Actually it's the Cruising and Sailing Forum.

Also most here aren't actually cruising and have way more power than is necessary so spending too much for a cruise you might take one day can be quite a waste of money

The forum URL is clickbait. I came here for cruising. There plenty of pure sailing forums around for those sailing after work, weekends, or holidays.

Back on topic, it is common to overspec a solar array to cope with shading, winter etc..

[thomm225]

Originally Posted by mikedefieslife

The forum URL is clickbait. I came here for cruising. There plenty of pure sailing forums around for those sailing after work, weekends, or holidays.

Back on topic, it is common to overspec a solar array to cope with shading, winter etc..

Like I said, if you just had sailors on here that were cruising, there wouldn't be a lot of posts.

Even on this thread, I don't believe half these guys are cruising yet if they even have a boat.

As far as those of us out racing, or sailing after work, on holiday, weekends, and vacations we are considering cruising but in the mean time actually sail our boats!

Back to the topic, most folks considering going cruising don't need a lot of power to sail locally or coastal cruise. (while they plan and consider the cruising life)

An $18.00 PWM 20 Amp Controller can handle say 200 watts worth of solar but most don't need that much unless you just plan to live on your boat until you actually go cruising

It's all about what each sailor wants.......

[GTom]

Originally Posted by mikedefieslife

Back on topic, it is common to overspec a solar array to cope with shading, winter etc..

Absolutely. Here is my scenario:
Basics: 33' boat, 4 people, UK West coast, no/limited shore power

1. Insolation: often cloudy, though summer days are long. I am just planning panel placement but I see little chance that I can put a significant part of my array on non-shaded, ideal angle adjustable pole mount.

2. Power budget:
6 hours autohelm = 6-10Ah
24h Fridge = 30Ah (it's not the Caribbean )
8 hours chart plotter/GPS = 6-10Ah
Lights (cabin+nav+anchor) = 0-10Ah
Laptops = 0-30Ah
Phones charging, etc = 10Ah
Radar = 0-20Ah
Inefficiencies/losses = 5-20Ah
Total = 45-125Ah or 500-1500Wh.

According to this test (200W NON-SHADED panels delivering ~ 6-800Wh/day), a 300W array wouldn't be oversized for the above needs: