Generator Decision

[Mistroma]

Yes

Its 1% of capacity as measured by the victron BVM which takes current rate and capacity into account. However the real point is one does not need a generator. A decent inverter and a bit more battery capacity is much less expensive.

Thanks, I imagine the BVM has the "fudge" factor built in to align with Peukert's law and 1% seems reasonable.

A generator is useful but not essential, especially if only weekend sailing from a marina. Do you live on board at anchor? If so, how much solar and wind generation do you have? I only have 345W solar and a Rutland 913. It is OK for most of the season but I do need a generator at either end. I do live on the boat for about 6-7 months, mostly at anchor. I wouldn't be keen to see SOC drop from 90% to 75% after using the microwave. I don't run the engine to charge at anchor but would feel I needed to use either engine or generator when using my 850W microwave.

OP mentioned an extended cruise and will find his generator useful. Of course he might have 600W solar fitted.

 

[William_H]

I have an microwave on board and have a replacement model at home. Although both are rated at 700W. They draw about 1.2kW. This is measured a power meter attached to test them. I have a 2KW Honda generator linked to a victron multiplus which has a 1.6KW inverter which can combine the generator and inverter output. This works fine without the generator and is not a significant load as the multiplus only takes about 1% of battery capacity (390AH) per minute of use. If you use the multiplus to limit the generator output you can maintain a low noise level. In fact a 1KW honda generator would do as the multiplus can top up the output.

Regards

Duncan

You frighten me a little with the statement that generator is linked to the Victron multiplus inverter. This implies that the AC from the gene is paralleled to the AC from the inverter to boost power. Now this is feasable if the inverter is designed be slaved off the generator so that both ac supplies are in phase and identical frequency. However I was not aware any manufacturer provided this facility. The point is if the sources are not identical in phase and are paralleled then you can end up with effectively a short on the AC demolishing both inverter and generator. So warning don't any one try this paralleling of AC supplies unless you are sure. (it is like connecting 2 batteries in parallel where you don't know which terminal is pos and which is negative except they are both changing at 50 times per second and are 240v )
ol'will

 

[Mistroma]

You frighten me a little with the statement that generator is linked to the Victron multiplus inverter. This implies that the AC from the gene is paralleled to the AC from the inverter to boost power. Now this is feasable if the inverter is designed be slaved off the generator so that both ac supplies are in phase and identical frequency. However I was not aware any manufacturer provided this facility. The point is if the sources are not identical in phase and are paralleled then you can end up with effectively a short on the AC demolishing both inverter and generator. So warning don't any one try this paralleling of AC supplies unless you are sure. (it is like connecting 2 batteries in parallel where you don't know which terminal is pos and which is negative except they are both changing at 50 times per second and are 240v )
ol'will

No problem, the Victron Multiplus 1.6kVA unit is designed to work that way and augment a limited AC source. Probably why it costs around £700.

 

[rszemeti]

IMPEX range from Screwfix

They are Impax and I tried to check whether they are 3,000 rpm and couldn't find the answer

You won't find that answer, because they are not fixed RPM generators .. they are variable RPM, with an electronic invertor to produce the 230V/50Hz ... basically when producing 25W they run slow, tickover .. when running 1000W they will run at whatever RPM gives peak power.

"Inverter Generators" are great on varying loads, and in theory will use less fuel, and last longer .. but please, buy a better brand than Screwfix!

 

[rszemeti]

I have an microwave on board and have a replacement model at home. Although both are rated at 700W. They draw about 1.2kW.

Yes, that sounds about right, the "700W" figure is the amoutn of microwave energy delivered to the cooking cavity ... the 1200W is the amount of energy going into the PSU to produce that energy, 700W of that becomes microwaves, the remaining 500W comes out the vent at the back as heat from the magnetron etc.

Microwaves are rated on their RF heating power, not their input power!

 

[DuncanHall]

Thanks, I imagine the BVM has the "fudge" factor built in to align with Peukert's law and 1% seems reasonable.

A generator is useful but not essential, especially if only weekend sailing from a marina. Do you live on board at anchor? If so, how much solar and wind generation do you have? I only have 345W solar and a Rutland 913. It is OK for most of the season but I do need a generator at either end. I do live on the boat for about 6-7 months, mostly at anchor. I wouldn't be keen to see SOC drop from 90% to 75% after using the microwave. I don't run the engine to charge at anchor but would feel I needed to use either engine or generator when using my 850W microwave.

OP mentioned an extended cruise and will find his generator useful. Of course he might have 600W solar fitted.

No but I cruse for about 2 months each summer. I deliberately use a low power microwave as at the lower current Peukert's law has less impact, as would a larger battery bank. I don't tend to use the microwave that long so perhaps using it for about 5 mins a day has less of an impact. I have a couple of hundred watts of solar but find that at anchor I need to put the generator on once a day to top the batteries up and to run the immersion heater. However that can be at a time of my choosing to minimise disturbance if required. In addition I often limit the output of the generator as the input AC current limit on the multiplus can be adjusted. By limiting the Honda to 5 amps its much quieter.

 

[Mistroma]

You won't find that answer, because they are not fixed RPM generators .. they are variable RPM, with an electronic invertor to produce the 230V/50Hz ... basically when producing 25W they run slow, tickover .. when running 1000W they will run at whatever RPM gives peak power.

"Inverter Generators" are great on varying loads, and in theory will use less fuel, and last longer .. but please, buy a better brand than Screwfix!

OP is talking about a small £280 petrol suitcase generator. I don't believe I have seen one of those with normal rpm of 1,500. Pretty certain the Honda 20EUi runs at around 4,300-5,000 rpm. It is a pretty safe bet that the Impax model won't run at 1,500 rpm unless it's at tickover (assuming it has a variable throttle).

I would be very interested in the make and model of your suitcase generator in case I need to buy one. It is bound to be quieter than a high revving screamer. I'll certainly keep a note of it for future reference.

In line with my comments in post #7

I never did get a reply about the make and model he was talking about. I'm pretty certain he was quoting very old information relevant to built-in diesel gen-sets. I remember frequent comparisons of 1,500 vs. 3,000 rpm in that context. Petrol suit case models would be expected to rev. more and I don't remember ever finding one with either max. or fixed 1,500 rpm.

 

[Mistroma]

No but I cruse for about 2 months each summer. I deliberately use a low power microwave as at the lower current Peukert's law has less impact, as would a larger battery bank. I don't tend to use the microwave that long so perhaps using it for about 5 mins a day has less of an impact. I have a couple of hundred watts of solar but find that at anchor I need to put the generator on once a day to top the batteries up and to run the immersion heater. However that can be at a time of my choosing to minimise disturbance if required. In addition I often limit the output of the generator as the input AC current limit on the multiplus can be adjusted. By limiting the Honda to 5 amps its much quieter.

Makes sense, I'd expect almost daily generator use for most people with 200W solar. I think 100A draw from 390Ah battery is enough for Peukert's law to have an impact. Figures you gave would be nearer 0.4% and I'd expect actual impact to be more. I probably wouldn't have guessed 1% but wouldn't dispute it either.

I limit our Honda by only running one thing at a time. It does make it a lot quieter. I run charger, microwave, toaster, hair dryer and water heater. Each individual item is around 1,200W and around 5A. The Honda becomes a lot noisier if I go much higher by adding some smaller items. I rarely heat water using the generator. Normal engine use gives a couple of days hot water and solar showers are OK on other days. OP would always find a small 1kW Honda running flat out just for battery charging.

I have sufficient power most of the time but do need to run the generator at either end of the season. I usually try to run our generator after breakfast on those days. My wife will grab a shower and use the hair dryer before I switch charger on. Main advantage is that I get 40A when batteries are at their lowest point and able to take 40A plus whatever solar is providing. I often find that mains charger output is much lower if I leave charging until late afternoon.

I think that this is because I only use the generator when solar won't be sufficient. The batteries wouldn't be getting to 100% but would reach 88% or higher and that's high enough to stop them taking full mains charger output. Using the 240V charging early in the day usually allows solar to provide maximum charge for the amount of sun available and batteries end up quite a few % higher.

 

[DuncanHall]

I had a careful look at the data. I have a Raspery Pi running victrons Venus OS so the Victron data are logged. This summer when drawing 1142W AC over a 3 minute period battery went from 76.5% to 73.8%. Current was 128.48A. Battery terminal voltage was 11.7V (under load). There were other DC draws of about 5A so perhaps 0.09% per minute is nearer the mark. This ties in well with the rule of thum of divide AC power by 10 to get DC current.

 

[rszemeti]

In line with my comments in post #7

I never did get a reply about the make and model he was talking about. I'm pretty certain he was quoting very old information relevant to built-in diesel gen-sets. I remember frequent comparisons of 1,500 vs. 3,000 rpm in that context. Petrol suit case models would be expected to rev. more and I don't remember ever finding one with either max. or fixed 1,500 rpm.

You wont, the 1500RPM sets tend to be bigger diesel sets, with more low down "oommph".

The modern trend, with advanced electronics, is to put the full field voltage on the alternator at all times, and just run the engine to produce the actual power needed. The voltage coming off the alternator is irrelevant, it varies from typically 20 to 300V depending on RPM, and is fed into a circuit known as a "PFC" that draws current over the whole cycle and converts it to a fixed DC voltage on a capacitor. A secondary invertor is then used to form a 230V/50Hz AC feed from the DC supply. It involved more electronics, but it does mean the generator only has to run at sufficient RPM for the actual load it is required to power at the time. Smaller engines can be used, typically.

Personally, on a cruising boat, with sufficient space, I would always go for a silenced, quality, diesel set. If there was insufficient space (42ft and under) I would just use batteries off the main engine. Modern LiFePO4 batteries are significantly more effective than lead acid per unit volume, their price is coming down. Even a decen AGM battery would produc enough power to run a microwave without issue, providing you are not trying to cater for hundreds of people.

 

[Mistroma]

You wont, the 1500RPM sets tend to be bigger diesel sets, with more low down "oommph".

The modern trend, with advanced electronics, is to put the full field voltage on the alternator at all times, and just run the engine to produce the actual power needed. The voltage coming off the alternator is irrelevant, it varies from typically 20 to 300V depending on RPM, and is fed into a circuit known as a "PFC" that draws current over the whole cycle and converts it to a fixed DC voltage on a capacitor. A secondary invertor is then used to form a 230V/50Hz AC feed from the DC supply. It involved more electronics, but it does mean the generator only has to run at sufficient RPM for the actual load it is required to power at the time. Smaller engines can be used, typically.

Personally, on a cruising boat, with sufficient space, I would always go for a silenced, quality, diesel set. If there was insufficient space (42ft and under) I would just use batteries off the main engine. Modern LiFePO4 batteries are significantly more effective than lead acid per unit volume, their price is coming down. Even a decen AGM battery would produc enough power to run a microwave without issue, providing you are not trying to cater for hundreds of people.

Yes, I know that. I was just trying to find out how the 1,500/3,000 rpm thing had come about. I was certain it was old knowledge from many many years ago being brought up in completely the wrong context. However, I thought it might be possible that there was some information from a user manual being interpreted wrongly. Hence my request for make and model. I had no expectation of actually discovering a small fixed rpm suitcase petrol generator on sale.

I'm not keen to run the main engine just for battery charging and I bought my T105s in 2012 when LiFePO4 wasn't a sensible option. I paid approx. £1.09 per Ah for the T105s and considered that good value in 2012.

Solar is a game changer and overcomes some of the deficiencies of Lead acid cells. It is extending the life of my T205s and I don't need to consider replacement yet.

Last time I checked 180Ah LiFePO4 would cost about £2,000 (£1k - £1.5k for unbranded) and I'd stick with 450Ah T105s at £600 for a little while yet.

I agree that a decent AGM will produce enough power to run a microwave, same situation with flooded batteries. Recharging is the issue, not how much you can take out of a battery. Much better efficiency with LiFePO4 but still cheaper to fit more solar and charge inefficient Lead acid cells at present.

 

[robertager1962]

Just an update on the Generator subject. Apparently there are practically no 2 kw generators available throughout the UK. Not a pending Zombie apocalypse (as I first thought) but apparently the company that produces these engines in the Philippines has a problem with supply at the moment (I guess Honda must outsource their small engines as well.) There has been a massive demand by the US and it seems that this market is seen as more lucrative than the the UK, so the generator stock has been diverted there. (Maybe they are having the Zombie apocalypse (or perhaps the Hurricanes and Polar Weather is the cause.)) Apparently the stocks are expected to arrive in the UK in April sometime. If you want a generator, then you may be in for a wait I am afraid. I think the small ones are currently unaffected.

 

[fisherman]

Daughter just bought LiFepo, 80Ah, the thought being that the increased efficiency outweighs the lower capacity. £600 I think, plus all the bits for b to b charging and solar.

 

[lw395]

.... I had no expectation of actually discovering a small fixed rpm suitcase petrol generator on sale.

I'm not keen to run the main engine just for battery charging .....t.

The way I look at it, running the main engine just to charge batteries is undesirable, but if the reality is that you only do so a few times a year, then the damage it might do and the fuel inefficiency are of no consequence set against a proper generator install, and probably very cost effective compared to a suitcase generator which you can't use in rough weather.
The problem of the main engine not warming up if it's just idling and charging batteries can be got around with a wet Eberbasto, giving the bonus of hot water in the calorifier.
Obviously, different people use their boats differently, a weekend cruiser-racer that does a couple of longer cruises each season is a different compromise to a houseboat or full time ocean wanderer.

 

[rotrax]

First Mate likes a shower every morning. No problem when shore power is available, but more difficult on the hook without a thermo top type water heater. I renovated an ebay bargain 8KW Westerbeke genset. It cost £1600.00 all in, installed by my mate and myself. Our boat had the advantage of a dedicated generator garage, so pretty straightforward. A good bit of the total cost was van hire, engine hoist hire-to get it in and out of the hired van-and crane hire to lift it into the track we had pre made and installed temporarily in the rear cockpit. The genset, sitting on a piano trolley, was pushed along until the block and tackle could take it for the final lift and drop into position.

45 minutes every morning gives a tank full of hot water plus giving the batteries-550AH's-a good kick.

Previously a Kypor 2600 was used for the same job, run on the swim platform or foredeck depending on wind direction.

This years job is making a soundbox for the Westerbeke. It is an open model, from a commercial trip boat. Should make the 45 minutes a bit quieter!

 

[Mistroma]

The way I look at it, running the main engine just to charge batteries is undesirable, but if the reality is that you only do so a few times a year, then the damage it might do and the fuel inefficiency are of no consequence set against a proper generator install, and probably very cost effective compared to a suitcase generator which you can't use in rough weather.
The problem of the main engine not warming up if it's just idling and charging batteries can be got around with a wet Eberbasto, giving the bonus of hot water in the calorifier.
Obviously, different people use their boats differently, a weekend cruiser-racer that does a couple of longer cruises each season is a different compromise to a houseboat or full time ocean wanderer.

+1
Pretty much only time I run the engine at anchor is to heat water and charge batteries at the same time. Waste heat for water and alternator for charging. That only happens 1-2 times some years and never in others. I usually manage with stored hot water and solar showers for most of the summer. A wet diesel heater would be great but I couldn't justify it for a few hours each year outside peak sunshine months. Hot water isn't a great priority when temp. gets to mid. 30s.

A built-in gen-set would probably heat water almost as quickly using a calorifier as my boat has quite a small heating element.