A battery question

[Cuppa]

On another forum, not RV related. I have been conversing with a chap who has 400Ah of 'hybrid' AGM batteries (whatever that means) & has just fitted a new 300A alternator which he intends to charge them with via his crank battery. I am uncertain whether this is via a VSR or permanently paralleled but I doubt that this makes any difference to the question I want to ask.

He wants the high output alternator primarily to allow prolonged winching in 4wd situations. Personally I think it's unnescessary overkill.

Anyhow I have been discussing what a 300A alternator is likely to do to his 400Ah AGM's, in light of the generally recommended max of 20% of the capacity charging rate ie 80A for a 400Ah battery bank.

He seems quite happy that the internal resistance of the batteries will limit the charging current, & I know it will. He is also happy to accept that the batteries will never charge beyond around 80% & is willing to accept a potentially shorter battery lifespan as a result.

His (possibly correct) belief is that whilst the alternator may chuck a lot more than 80amps into the batteries when they are significantly discharged that this will only occur briefly & that the alternator output will not have a delterious effect on the battery, beyond warming them briefly in that early early stage of charging.

Is he correct? Why is the max 20% figure recommended. Is he going to prematurely kill his batteries through overcharging, even though they will never fully charge? I'm not sure if I'm missing something, but somehow it just doesn't seem like a great idea to me.

[Peter and Sandra]

Having done very similar many years ago with normal LA batteries albeit with much less alternator output my first thought is that the AGM's might not like it all. In my case we only had two 100ah LA's and what at the time was a huge output 100 amp alternator.
I reality the alternator worked fine until the batteries were virtually flat then as the alternator started to take a greater percentage of load it quickly got very hot and something inside melted and shorted and that was the end of that.
The problem was that back then alternators rarely had internal temperature sensing so they could self limit output as they heated up, most alternators today will have temperature limiting built in. He might find that achieving the alternators rated output is nigh on impossible.
The other factor is at what point does his alternator achieve peak output, having to have the engine at high revs to achieve the high output wears thin pretty quickly and is also not possible to do if winching and driving at the same time.
Put simply if as we decided back then if you wish to winch for more than five minutes at a time then a PTO winch is the only way, electric winches are fine for self recovery in short spurts as the second factor is that winches are often mounted behind bumper bars with little airflow and heat up very quickly when working hard. One reason the high mount Warns were very popular for hard core use, the motor is sitting up in the breeze.

[BruceS]

I'd love to know how he is driving that alternator?
You'd want either at least 3 belts or a wide serpentine one. Maybe engine driven in the back of a ute?
Most batteries they use in houseboats specify 10%. 600Ahr @ 60A.
I suggest he better make sure there are no sparks around if flat out charging them. OK, VRL but the valve might 'pop' I reckon?

[bagmaker]

AGMs wouldnt be my first choice of battery here.
Lithium would be, failing that, normal flooded lead with a high CCA.
AGMs might be a bit fragile and light internally.
Or perhaps thats what the "Hybrid" tag means?

[T1 Terry]

He has it right about the winching killing the alternator, lots of stories about just that happening. The next bit is about the internal resistance of the lead acid batteries stopping over current charging, also on the money, as long as the charging voltage is limited to the upper acceptance level specified by the manufacturer, no problems. Even when deeply discharged, once the plate surface becomes saturated because the chemical conversion is too slow to absorb the current, the voltage will climb rapidly and the alternator voltage level will be reached resulting in a reduction of the output current.
Bruce mentions a very serious issue with high output alternators, actually driving them via belts. Off road, forget about the wide serpentine belts, the dust will build up in the crankshaft pulley and either throw the belt off or as soon as the load is applied the dust will become an abrasive compound and tear the grooves out of the drive pulley .... then the belt slips and the rubber belt actually cuts the steel pulley to pieces, not the belt, you can see that happen where rubber seals run on steel shafts and the "V" in a standard type drive pulley actually tear out to the point the belt will no longer grip.
The design/build the set up he will need to seek advice from Gates or any of the well known belt manufactures as to the type of belt and V section of the pulleys, it is a very complex subject.
As far as over heating and spin speed, a specially built alternator is required, most commonly used for blue water cruising boats because they need to recharge very big battery banks via a diesel powered genset. There is also a purpose built voltage regulator/alternator control unit required for this application. Balmor is probably the best known brand and they have a world of experience.

By far the easiest method is as Bagman has suggested, turn the engine off and power the winch via a lithium battery pack. It will require either a specialised alternator control unit or a DC to DC charger to protect the alternator while recharging the lithium battery pack so it doesn't burn out and the battery can not be mounted under the bonnet beside the engine. This goes for any chemistry battery besides flooded cell batteries because only they can have water added to replace the electrolyte lost due to the heat.
Electric winches are great, but as Perter and Sandra have mentioned, cooling is very important. I've seen water spray units set up over the electric motor and planetary gearbox to move some of the heat away. There are also EV fluids developed by Total and Shell among others that are desighed to pump through the electric motor to act as a coolant, maybe another area to look into for future winch upgrades, but a VFD and AC (brushless DC motor) would be advisable so the brushes don't get rubbish build up and state jamming in the holders. Many people overlook the heat build up the brushes suffer and can get high enough to affect the spring tension applied to hold them against the armature. Electric motor drives have come a long way with the emergence of electric vehicles, maybe even a modification of the Fisher and Paykel drive motor could be utilised to provide huge torque at slower winch speeds yet no contact between moving parts in the electrical area

T1 Terry

[jon_d]

How much current does the winch draw under full load?

[Cuppa]

Thanks all. Earlier I copied & sent the chap Peter's reply via PM. For completeness I have copied his reply to that below. I had already suggested drive belts may be an issue having found reference to that on sailing forum, as Terry has now mentioned too. I might add that I don't understand his comment about 'additional rectifier pack, which boost the charge heat dissipation to over 420 amps over and above the 300 amps in the alternator' The comment about there being less load on a rear winch set up makes sense to me, but if correct seems to negate the need for the higher amp unit to my way of thinking. I may be wrong buti t all still sounds more like 'big boys toys' than a need being usefully met to me. He's a nice bloke, & I think I've taken it as far as I'm going to with him.

Thanks Cuppa, This alternator is a new generation high output unit from the USA. It can put out 200amps at idle, 300 peak, and coupled with the additional rectifier pack, which boost the charge heat dissipation to over 420 amps over and above the 300 amps in the alternator, the rectifiers will all remain cool even under the intense heat of the bonnet. As previously stated, I doubt the 300amps will ever come into play unless winching. I have no doubt the 300amps is avail when required, simply from my research on this particular unit. @MB has a monster alternator, can't recall the make or size but it also has a similar charge profile - we are STILL waiting for that unit to make its way into service, which would be a good comparison. Its a rear 15000lb warn electric. If you recall, generally its a lot shorter distance to recover in reverse than forward , and the load is less as the path has already been cleared on the way in, hence the winch load will be lower. Its got 40m of rope on it, so doubled up, no hurry, half the amps required, so will be fine.
I accept the comments about the engine rpm issue, but for the rear recovery situation I will be outside the car anyway, with a hand throttle on the engine - still trying to dream an assy up as the chev throttle linkages are a bit difficult to reconfigure. For the heavy lifting tasks that's why I went the hydraulic, which is run off a PTO on the gearbox. It has pulled me an honest mile, with 25m pulls on a track in Vic that was simply like greased glass to stand on after a night of rain. It is better than the mechanical PTO as the overload device is a pressure setpoint and if its exceeded the oil bypasses - simple job to re-rig for multi line pull, as opposed to the shear pin assy of the old PTO. the high mounts are a favourite , but after having 2 of them, don't rate them without '000's of additional mods - again, its a winch that has been repurposed and operated for very short bursts and it wont last the distance like a correctly rated one will.

Finally regards the OP's experiences, I think he explains the reason for root cause failure, and that is the alternator was too small for the implied load, the battery voltage dropped to hopelessly low and basically catastrophic levels and the alternator was trying to compensate for the low voltage and the load - all recipe's for disaster, as he experienced. If the batteries get hot, yes the pop, especially AGM - have had 2 die like this in the past, but suspect it was internal construction failure that collapsed the plates and gel and all over, not a load issue.

I will add that he recently, during what he described as a 'brain fart' connected the alternator to his battery bank via a Ctek D250s with smartpass (max input current 120A). The result was the Smartpass below. After he'd finished kicking himself & posted the pic someone posted a comment which tickled me "That should buff out ok".

attachment.jpg

[Cuppa]

How much current does the winch draw under full load?

Not sure about his Jon, but mine which is a smaller 9,000lb unit can draw around 450A at full noise. The few occasions that it's seen use in my hands it would have been drawing probably no more than half that.

[T1 Terry]

How much current does the winch draw under full load?

Not sure about his Jon, but mine which is a smaller 9,000lb unit can draw around 450A at full noise. The few occasions that it's seen use in my hands it would have been drawing probably no more than half that.

At half load that is still 225 amps and will quickly overheat and kill an alternator. An automotive rated alternator is not designed to run at full output for more than a minute, so say 100 amps for 1 minute and that should have been enough to get the start battery recharged to replace what the starter motor used on a cold morning restart. With the alternator already at operating temperature, it doesn't take very long at full load to overheat and start burning the lacquer off the windings and melting the solder where the windings are soldered into the commutator. High output alternators have additional fans and superior winding insulation to protect against overheating under high loads, the special alternator controller also has a temp sensor that reads the alternator winding temp and backs off the load if it gets hot. There are some that can even sense belt slip and alter the load constantly to remain just at the point of slip.
The upgraded rectifier pack is the bit on the output side of the alternator that changes the AC output from the alternator into smooth DC suitable for battery charging and powering DC devices. By improving the component quality the current transfer to heat generation can be improved so I'm guessing that is what is happening there.

T1 Terry

[jon_d]

If the winch is drawing less than 300 amps, and if the battery is full. - then all the alternator current will go to the winch.

The charge current into the battery only becomes a problem when the battery is flat.

My understanding is that AGM charge current should be limited to 1/10 of the total A/H capacity. Hence why chargers have 3 stages.

Bulk = constant current @ 1/10 A/H up to a set voltage point
Absorb = constant voltage at slightly higher than float and current < 1/10 A/H
Float = constant voltage and then dropping into Bulk is discharge pulls battery voltage below float setting


Basically, he's trying to extend the winch time but as others have said, the duty cycle of the winch may be limiting factor now.

A 3.6kw continuous alternator will be huge. I'd be guessing at about 23 kilos.
I'm surprised it can be mounted on the engine. Is there a link to the said alternator?