Charging- help me understand this?

[Ricco1]

I mainly rely on solar but at this time of the year I need to run my engine more.

 

I recently salvaged a cheap 2 stroke generator from a CRT disposal site. Replaced the ht lead, got it up and running. I've just used it for the first time,was pretty shocked with the result!

 

Bit more info: I monitor my batteries by reading the volts on a meter attached to my mppt solar controller. My engine alternator is 40 amps. The generator is rated at 650 watts, I connected it to my landline connection which in turn is attached to a 20 amp battery charger.

 

What was shocking? well with the voltage at the time, I would have expected the engine to take the batteries to 14.3v, engine running, they are then fully charged. The generator got to that voltage in 15 minutes.

 

This suggests to me that the alternator isn't working properly. Is it possible for an alternator to work, but not properly, only putting a tiny charge in rather than what you might expect? If so, can this be repaired?

 

I know I need a clamp meter, one is on order, just thought I'd sound out some opinions on this.

 

Thanks.

[Tony Brooks]

I mainly rely on solar but at this time of the year I need to run my engine more.

 

I recently salvaged a cheap 2 stroke generator from a CRT disposal site. Replaced the ht lead, got it up and running. I've just used it for the first time,was pretty shocked with the result!

 

Bit more info: I monitor my batteries by reading the volts on a meter attached to my mppt solar controller. My engine alternator is 40 amps. The generator is rated at 650 watts, I connected it to my landline connection which in turn is attached to a 20 amp battery charger.

 

What was shocking? well with the voltage at the time, I would have expected the engine to take the batteries to 14.3v, engine running, they are then fully charged. The generator got to that voltage in 15 minutes.

 

This suggests to me that the alternator isn't working properly. Is it possible for an alternator to work, but not properly, only putting a tiny charge in rather than what you might expect? If so, can this be repaired?

 

I know I need a clamp meter, one is on order, just thought I'd sound out some opinions on this.

 

Thanks.

 

 

Yes it is possible, like when a diode fails so you loose one of the generating coils. However I would not expect an alternator with a stator coil out to produce 14.3 volts. If this is the fault then it can be repaired by changing the diode pack but that involves some fast soldering.

 

I wonder if the charger is being too cleaver for its own good but we will not know without current and voltage readings and unless you cover the panels any solar voltage will mess up any inference we can draw from just the voltage.

 

Usually a fast recharge indicates sulphated batteries but if the alternator charge and the generator charge have been done within days of each other this is unlikely.

 

By the way 14.3 volts form the alternator normally indicates its regulator has started working and the batteries will be far from fully charged by some hours. A much better indication is when the charging current has dropped to around 1% (or a bit more) of battery bank capacity.

 

I would be interested in Nicknorman's take on this now SirN hardly ever drops in

[Paul C]

 

I would have expected the engine to take the batteries to 14.3v, engine running, they are then fully charged.

 

 

This is the incorrect bit

[Loafer]

If your batteries are wet lead-acid and not sealed, then they're fully charged when at 14.8V with the charge current having reduced to 1-2% of the total battery capacity.

 

EG

 

A 400Ah battery bank is fully charged when the voltage is at 14.8 and the charge current has reduced to 4-8 Amps. This takes about 6-8 hours on a half-charged battery bank IF you have 1/10 of the battery capacity in charge current. (40Amp charger = OK)

 

Get another opinion from the old sweats here but I think thats right - and that's what I do.

Edited October 28, 2015 by Loafer

[bottle]

I cannot say you have or have not a problem but your understanding of voltage and amperage as regard to battery charging are a bit amiss.

 

 

With a discharged battery then the voltage will start low (12.2, 50%SOC) and the amps high as high as the chargers maximum (not an alternators as you will probably not be spinning fast enough) and as charging takes place the voltage will rise and the amps become low.

 

A battery is deemed to be fully charged when it has been at the maximum voltage the charger can supply and the amps are approximately 1% of the battery capacity.

 

 

Here is a site that may help with understanding batteries and charging:(not checked) http://www.batteryfaq.org/

[by'eck]

The time it takes a voltage limited charge source such as engine alternator or mains charger to reach the limit is dictated by the ratio of charge amps available to battery capacity. A high current source could force considerable current into a battery bank allowing them to hit the the voltage limit well before they are fully charged due to surface charge effects.

 

All the comments regarding relying on charge voltage as an indication batteries are fully charged assume a modest charge source current, say around one tenth of (actual) amp hour capacity of battery bank. If the batteries are old the amp hour capacity may have dropped considerably, meaning you now have a much higher charge current to amp hour ratio and leading to greater inaccuracies when using charge voltage as a reference.

[Ricco1]

I should have added: I'm making the assumption that the batteries are fully charged at 14.3/ 14.4 volts on the basis of my Tracer solar controller. When the panels are working and the batteries fill up a green light flashes on the controller, the amps then drop considerably and voltage gets no higher. The same light flashes when I'm charging the batteries via the engine or as earlier, with a generator.

[ditchcrawler]

I should have added: I'm making the assumption that the batteries are fully charged at 14.3/ 14.4 volts on the basis of my Tracer solar controller. When the panels are working and the batteries fill up a green light flashes on the controller, the amps then drop considerably and voltage gets no higher. The same light flashes when I'm charging the batteries via the engine or as earlier, with a generator.

I would guess that the light is triggered by the battery voltage and as you are not charging via the controller you have no idea of the current.

[Paul C]

I should have added: I'm making the assumption that the batteries are fully charged at 14.3/ 14.4 volts on the basis of my Tracer solar controller. When the panels are working and the batteries fill up a green light flashes on the controller, the amps then drop considerably and voltage gets no higher. The same light flashes when I'm charging the batteries via the engine or as earlier, with a generator.

 

That's a reasonable assumption but unfortunately its not a very good one. Solar controllers aren't especially good at charging efficiently, basically they are very conservative and the last stages of charging are very gentle. Their advantage is that they charge all the time it sunny, so in a typical summer's day will fully charge the battery. At this time of year, they begin to show their weakness and in the winter need an alternate charge source because there's not enough sunlight to do more than about 10% of what they can in summertime.

[matty40s]

I should have added: I'm making the assumption that the batteries are fully charged at 14.3/ 14.4 volts on the basis of my Tracer solar controller. When the panels are working and the batteries fill up a green light flashes on the controller, the amps then drop considerably and voltage gets no higher. The same light flashes when I'm charging the batteries via the engine or as earlier, with a generator.

Most bulk charging will happen at a voltage similar or above the Tracers default max voltage switch which drops it into float ( signified by flashing green).

This is why you can cruise in summer and not have your batteries fried by excess solar input.

 

Your batteries will be fully charged when they are sat at 13.5-8v with virtually nil ampage going in. 14.4-8v is bulk charging voltage.

[Ricco1]

 

That's a reasonable assumption but unfortunately its not a very good one. Solar controllers aren't especially good at charging efficiently, basically they are very conservative and the last stages of charging are very gentle. Their advantage is that they charge all the time it sunny, so in a typical summer's day will fully charge the battery. At this time of year, they begin to show their weakness and in the winter need an alternate charge source because there's not enough sunlight to do more than about 10% of what they can in summertime.

 

Sure, I run my engine for an hour or so each day now, have for a month or so. In the summer I didn't need to run it at all.

 

I guess what I'm trying to understand here: I have my way of reckoning whether the batteries are reasonably well charged or not. I understand that I might not have got this right, I've a lot to learn. But my method of measurement is consistent, both with engine and alternator. This being the case I can't understand why a generator connected to a battery charger rated at 20 amps does the job in 15 minutes whereas the 40 amp engine alternator takes 4 times as long.

Most bulk charging will happen at a voltage similar or above the Tracers default max voltage switch which drops it into float ( signified by flashing green).

This is why you can cruise in summer and not have your batteries fried by excess solar input.

 

Your batteries will be fully charged when they are sat at 13.5-8v with virtually nil ampage going in. 14.4-8v is bulk charging voltage.

 

Ah right I didn't realise that. What percentage charge are the batteries at when the bulk charging phase changes to float?

[matty40s]

Impossible to tell from the tracer panel SOC reading, it is not worth using.

[Loafer]

Most bulk charging will happen at a voltage similar or above the Tracers default max voltage switch which drops it into float ( signified by flashing green).

This is why you can cruise in summer and not have your batteries fried by excess solar input.

 

Your batteries will be fully charged when they are sat at 13.5-8v with virtually nil ampage going in. 14.4-8v is bulk charging voltage.

Not according to Trojan Batteries. 14.8V with 1% capacity charge current = fully charged. Being sat at 13.5-13.8 with negligible charge current is the way to KEEP them there. That's what I gather, anyway.

 

If you get a good MPPT controller, you can override the controller manufacurer's defaults and keep the controller going at 14.8V, or better at say 14.6, so that the batteries don't gas on a long hot day.

 

Also - the Tracer's SOC gauge is about as useful as sticking your tongue onto the terminals! Watch it go up and down as the sun goes in and out!

 

ETA The SOC, not your tongue!

Edited October 28, 2015 by Loafer

[Paul C]

 

Sure, I run my engine for an hour or so each day now, have for a month or so. In the summer I didn't need to run it at all.

 

I guess what I'm trying to understand here: I have my way of reckoning whether the batteries are reasonably well charged or not. I understand that I might not have got this right, I've a lot to learn. But my method of measurement is consistent, both with engine and alternator. This being the case I can't understand why a generator connected to a battery charger rated at 20 amps does the job in 15 minutes whereas the 40 amp engine alternator takes 4 times as long.

 

Ah right I didn't realise that. What percentage charge are the batteries at when the bulk charging phase changes to float?

 

I think this illustrates why you need proper battery monitoring; and (Smartgauge excepted) why measuring current in addition to voltage, is so useful. By measuring current you have the information you need to know what's going on at all times.

ETA: Let's not forget that accurately defining and measuring 100% SoC is a bit of an aspiration - luckily you don't need to, in fact it doesn't help much anyway because batteries lose their capacity from day one, so you can never be entirely sure of how much energy you have available etc. Smartgauge + amp hour counting and proper interpretation (like nicknorman's setup) gives the opportunity to interpolate the two readings of SoC and determine the actual capacity you have, thus at a given SoC you know the capacity remaining, which is useful to know.

[by'eck]

Ah right I didn't realise that. What percentage charge are the batteries at when the bulk charging phase changes to float?

 

Multi-stage mains chargers and external alternator regulators charge at the higher absorb voltage for a timed period. Early versions had a fixed or sometimes user adjustable time for this phase dependant on battery capacity. Newer ones calculate bank capacity and so time required automatically, but often seem to underestimate allowing the unit to drop to much lower float voltage before batteries are fully charged. Consequently a definitive answer is not possible but ideally should be close to fully charged. If in doubt recycling charger will force it through all charge phases again.

[Ricco1]

Thanks for all the replies. I never realised I knew so little about the subject.

 

I guess I'm a belt and braces guy at heart. There's something I still don't understand:

 

Rested batteries at 12.4v. I assume they are around 70% charged. I decide to charge them.

 

1/ when I run my engine, 40a alternator, the voltage measured on my Tracer 'meter', plus another cheap voltmeter I have elsewhere on the boat goes up to around 13.5. It then goes up to 14.3/14.4 slowly, taking an hour or more. At this stage I (incorrectly as it turns out) assumed the batteries were pretty well charged.

 

2/ the generator, connected to a 20a battery charger also goes to 13.5 straight away but then goes up very quickly to 14.4, in less than 20 minutes.

 

This made me think that something is wrong somewhere. Why should a lesser alternator increase voltage much quicker than one twice it's size? Does this suggest that there's something wrong with the engine alternator or is this experience an illusion, the reality is that my engine is charging just as quickly with the engine, it just doesn't appear to be doing so?

[ditchcrawler]

Thanks for all the replies. I never realised I knew so little about the subject.

 

I guess I'm a belt and braces guy at heart. There's something I still don't understand:

 

Rested batteries at 12.4v. I assume they are around 70% charged. I decide to charge them.

 

1/ when I run my engine, 40a alternator, the voltage measured on my Tracer 'meter', plus another cheap voltmeter I have elsewhere on the boat goes up to around 13.5. It then goes up to 14.3/14.4 slowly, taking an hour or more. At this stage I (incorrectly as it turns out) assumed the batteries were pretty well charged.

 

2/ the generator, connected to a 20a battery charger also goes to 13.5 straight away but then goes up very quickly to 14.4, in less than 20 minutes.

 

This made me think that something is wrong somewhere. Why should a lesser alternator increase voltage much quicker than one twice it's size? Does this suggest that there's something wrong with the engine alternator or is this experience an illusion, the reality is that my engine is charging just as quickly with the engine, it just doesn't appear to be doing so?

So how much voltage is dropped between the B+ terminal on the alternator and the positive battery terminal when the charge rate is quite high? This assuming it is not a battery sensing alternator and just a bog standard one, also if its an insulated return how much is dropped between the battery -ve terminal and the alternator -ve terminal ?

[bottle]

 

This being the case I can't understand why a generator connected to a battery charger rated at 20 amps does the job in 15 minutes whereas the 40 amp engine alternator takes 4 times as long.

 

This goes back to my post, you are not spinning the alternator fast enough and will not unless you rev the b*ll*cks of your engine.

 

Assuming your engine is modern and the alternator to engine pulley is three to one then for the alternator to start useful generation will need to spin at 3,000+ rpm so the engine will need to spin at 1,000+ rpm. At those speeds the alternator will not give its maximum output.

 

Alternators depending on models can be spun up to 15,000+ rpm though they do tend to give decent output at lower figures say about 6,000 rpm so in that case your engine would need to be spinning at 2,000 rpm (hence the b*ll*cks of your engine.)

 

I have an 80 amp (24v) alternator ( like all alternators in standard form it is dumb ) and a 50 amp 'intelligent' charger and that charges the battery bank faster.

 

The alternator also only gives a maximum charge voltage of 28.8v but the charger can give 29.2v but to do that it checks the battery temperature.

 

The batteries are AGM deep cycle, the ideal figure for your batteries will probably be different.

 

ps. for a 12v system half the voltage figures but the spin speeds will remain the same.

.

[Iain_S]

The alternator may not be spinning fast enough to generate 40A. Before it reaches 14.3V, it is passing as much current as it can. Once the battery has taken an initial charge, the alternator voltage is regulated by its voltage regulator, which holds the voltage steady. The current then gradually reduces as the battery charges. This takes a few hours, usually.

 

As an example, Gamebird (Vetus 2.04 engine) has a 30 A alternator, which is not very highly geared. If the batteries are below 70% or so, I have to run the engine at 2000 r.p.m. to get 30A or so. After 15 minutes or so, the current reduces, and I can cut back engine r.p.m. Eventually, I get to about 10 Amps at 14.2V. It takes about another 4 hours running before the batteries are charged. Obviously, timings vary a bit depending on the starting S.O.C., but under 4 hours cruising usually means the batteries are not fully charged.

[Paul C]

 

This goes back to my post, you are not spinning the alternator fast enough and will not unless you rev the b*ll*cks of your engine.

 

Assuming your engine is modern and the alternator to engine pulley is three to one then for the alternator to start useful generation will need to spin at 3,000+ rpm so the engine will need to spin at 1,000+ rpm. At those speeds the alternator will not give its maximum output.

 

Alternators depending on models can be spun up to 15,000+ rpm though they do tend to give decent output at lower figures say about 6,000 rpm so in that case your engine would need to be spinning at 2,000 rpm (hence the b*ll*cks of your engine.)

 

.

 

....which is child's play to determine, with an ammeter....

[bottle]

but only if that child has one, has the knowledge to use one and know what it (the child) is being told.

edit: it repeated , slow internet connection keeps dropping out

Edited October 29, 2015 by bottle

[Paul C]

Its not complicated! You connect the ammeter so it reads the current being put into the batteries from the alternator. If you have a fixed shunt installed in the negative terminal, then turn off other chargers and loads; if you have a clamp ammeter connect it around the lead from the alternator. Slowly increase the revs and observe the ammeter's display.

[bottle]

I know, I do it nearly every day but if you have not been shown, taught etc. then it is all gibberish.

[dmr]

There are at least three things to get a grasp of here, and an ammeter will help enormously.

 

A 40 amp alternator will rarely produce 40 amps. If its spinning fast and stone cold it just might manage it for a short while.

If its hot and/or not spinning fast then 20 amps or even much less would not be unusual.

 

14.4 volts is low. It will take AGES to charge a flooded lead acid battery at 14.4.

About 14.8 is correct but only makers of tough batteries like Trojan suggest this.

Many suppliers of "leisure" batteries, makers of chargers, and "experts" are happier with 14.6 or even 14.4 volts.

They are just "playing safe", reducing the amount of topping up required, and causing you to waste a huge amount of fuel trying to charge at this voltage. Maybe your charger charges at more than 14.4? If you leave it running after you get to 14.4 does the voltage keep on increasing???

 

There is also the issue of "soft" regulators in alternators. Ideally the alternator should run flat out till its voltage is reached (14.4 or 14.8 or whatever) and only then ease off to hold that voltage. In reality a lot of alternator regulators start to ease off too soon and approach their target voltage too slowly.

 

For any or all of these reasons your charger just does it better than the alternator.

 

.............Dave

[Loafer]

An alternator isn't really a charger, either. It's a dumb-ass lump designed to put back 10 secs' worth of engine starting, and to prop up the battery voltage if you're using the car's services (like stereo or lights). Or has all that changed now? Can we get alternators for boats that charge in stages, like proper chargers?