Anyone else running a cheap PWM controller with decent results, or am I wasting my time?

Picked up a 20A PWM controller off eBay for about £8 delivered — a generic unit, no brand worth mentioning — and paired it with a single 100W panel and a tatty 110Ah leisure battery I rescued from a mate's caravan. Wiring it all up in the van this weekend, mainly to run a 12V compressor fridge and keep the phone and laptop ticked over.

I know everyone bangs on about MPPT being the way to go, and yeah, I get the efficiency argument. But for a small setup like mine, with one panel and a battery that probably only holds 80% of its rated capacity anyway, I'm struggling to justify spending £40-60 on even a budget MPPT when the whole point is to keep costs down. The maths just don't seem to stack up at this scale.

Had it running on the bench for a couple of days and the battery is hitting 14.1V on a decent sunny afternoon, which seems reasonable to me. Bulk charge cuts in fine, float seems stable around 13.6V. Nothing has caught fire yet, which I'm counting as a win.

Has anyone actually done a proper side-by-side comparison at this kind of scale — single panel, smaller battery — and found the PWM genuinely couldn't keep up? Or is the MPPT obsession more relevant once you're running multiple panels?

@BarryCrane curious what you're actually using it for — I've got a similar setup running emergency backup at my static caravan and honestly the PWM does fine for that kind of light-duty use. Keeping a battery topped up, running a few LEDs and a 12V pump now and then — no complaints.

Where I did notice a real difference was panel efficiency in anything other than full sun. A Renogy MPPT (even a cheap 10A one) pulls noticeably more from the same panel on overcast days, which in the UK is basically most days.

So I'd say: if you're not pushing the system hard and your expectations match the hardware, you're not wasting your time. But if you're frustrated by sluggish charging through autumn and winter, that's likely your culprit rather than a fault.

@BarryCrane Honestly, for a single 100W panel into a leisure battery, a cheap PWM is perfectly adequate — you're not losing sleep over MPPT efficiency gains at that scale. The maths just doesn't justify spending £40+ on a proper MPPT controller when your panel's max output is modest anyway.

The weak point in your setup is almost certainly that "tatty" battery rather than the controller. A knackered leisure battery with reduced capacity will mask any gains you might otherwise see. Worth doing a proper load test on it if you haven't already.

I ran a similarly specced generic PWM unit for two years without drama — just make sure the temperature compensation is set reasonably and keep an eye on your charge voltages. What are you seeing on the meter for absorption voltage? That'll tell you a lot about whether it's behaving sensibly.

Just to add to what @KeithWebb is getting at — the main thing with these cheap units isn't really the PWM technology itself, it's build quality. I've had a couple of those eBay specials and the weak point is usually the temperature compensation (often nonexistent) and the charge set points being slightly off from factory. Worth chucking a multimeter on the battery terminals occasionally to check it's actually hitting absorption voltage properly — around 14.4–14.7V for a flooded leisure battery. If it's only reaching 14.0V or lower, you might be chronically undercharging and shortening that battery's life without realising. A quick tweak of the pot inside (if it has one) can sort it. For a 100W panel into a 110Ah battery you're hardly pushing it hard, so honestly you're probably fine. Don't overthink it.

Good shout from @Spud99 there. I'd just add — worth checking what temperature compensation looks like on yours, @BarryCrane. A lot of these budget units claim it but either lack the sensor or the algorithm is frankly rubbish. In practice with a leisure battery sitting in a shed through a British winter, you can end up with chronic undercharging without realising. Not a dealbreaker, just worth knowing. I ran a near-identical setup for two years on my shed workshop and it was fine for what it was — lighting and charging drills mostly. The losses versus MPPT genuinely don't matter at that scale. Where people come unstuck is expecting these cheap units to last five years without any fuss. Keep an eye on the connections every few months and you'll be alright.

@BarryCrane one thing nobody's mentioned yet — check your PWM controller's low-voltage disconnect setting. The cheap units often ship with LVD set aggressively low, sometimes 10.5V or even 10.8V, which will genuinely damage that leisure battery over time by allowing deep cycling well below what the chemistry tolerates. I'd want to see LVD no lower than 11.8V for a flooded lead-acid being used regularly.

Also worth confirming it's actually PWM and not just a basic on/off shunt controller with misleading labelling — at £8 delivered you're in genuinely ambiguous territory. Real PWM should show a pulsing voltage during bulk/absorption. A multimeter across the battery while charging will tell you quickly enough.

For a 100W single-panel setup the efficiency gap versus MPPT is minimal anyway, so you're not wasting your time — just keep an eye on those protection thresholds.

Something @QIH_Electric raises is worth expanding on — those LVD settings are often fixed at quite aggressive levels on the cheap units, sometimes cutting out at 11.4V or lower, which by that point you've already done real damage to a leisure battery. If yours has adjustable LVD, nudge it up to around 12.0-12.1V and you'll get considerably more cycles out of that rescued battery.

Also worth mentioning since nobody's touched on it — keep an eye on the controller's own current draw at night. Some of these no-name units have surprisingly parasitic quiescent draws, I've seen figures pushing 20-30mA on similar boards, which quietly nibbles away overnight. Dead easy to measure with a clamp meter on the battery cable after dark. Small thing but adds up across a full winter when your panel isn't doing much.

On a 100W panel with PWM you're basically leaving 20-30% of your potential harvest on the table — but if the £8 controller doesn't fry your battery, that's still free electricity from a rescued leisure cell, which is hard to argue with.

When I upgraded from a similar bodge-job to a Victron MPPT the difference on cloudy days was almost embarrassing — PWM just gives up when the sun goes shy, and we all know how rarely that happens in Britain. 🌧️